3rd Workshop on Current Trends in Molecular and
Nanoscale Magnetism
Welcome from the Workshop Chair
It is with great pleasure that I welcome you all to the 3rd
CTMNM Workshop being held at the beautiful Disney Swan and
Dolphin Resort in Orlando, Florida. This is the first time that this
meeting has been held outside of Greece, and I am very pleased
and proud that the 2010 meeting is in Florida, a state with a long
and deep tradition in magnetism research of all kinds.
I think you will agree with me that we have an exciting program
of talks to look forward to this week, with speakers junior and
senior, experimentalists and theorists, from areas spanning
chemistry, physics, and materials science. I am particularly
pleased that so many colleagues from the North American
magnetism community are able to attend, providing a rare
opportunity for us to meet on our own continent! Of course, I am
also very grateful to those who have traveled here from farther
afield.
I want to acknowledge the support of our various sponsors, without which we would not have
been able to put this workshop together. I am particularly grateful to our corporate sponsors
Cryogenic Ltd and Strem Chemicals. I also received great support from the Florida universities I
approached, the University of Florida, Florida State University, and the University of Central
Florida, as well as the National High Magnetic Field Laboratory in Tallahassee.
Finally, my thanks go to several people: I thank the members of the Christou group, who kindly
volunteered their time and services to provide the local muscle and audio-visual expertise
required for running the workshop; the staff of the Disney Swan and Dolphin Resort, who bent
over backwards to help us put on this workshop; and last but not least, to my Program Assistant
Ms. Alice Jempson – it would not be an overstatement to say that she single-handedly organized
essentially the whole meeting from its inception to its execution; a Herculean effort over many
months that also involved tackling all the various problems and glitches that arise in such an
enterprise – and always with a smile on her face.
Thank you all for being here and I hope you have an enjoyable and stimulating meeting.
Sincerely,
George Christou
George Christou
Chair, Organizing Committee
THANK YOU TO OUR SPONSORS
SWAN BALLROOM
Registered Participants
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Achim, Catalina-Carnegie Mellon University
Aeppli, Gabriel-London Centre for
Nanotechnology
Alexandropoulos, Dimitris-University of Patras,
Greece
Chen, Lei-Florida State University
Chiorescu, Irinel-Florida State University
Christou, George- University of Florida
Chudnovsky, Eugene – CUNY Lehman College
Dalal, Naresh-Florida State University
Datta, Saiti-National High Magnetic Field
Laboratory
Del Barco, Enrique-University of Central
Florida
Dumont, Matthieu-University of Florida
Dunbar, Kim-Texas A&M University
Efthymiou, Constantinos-University of Florida
El Hallak, Fadi-London Centre for
Nanotechnology
Fishman, Randy-Oak Ridge National
Laboratory
Friedman, Jonathan-Amherst College
Gangopadhyay, Shruba-University of Central
Florida
Garg, Anupam-Northwestern University
Ghosh, Sanhita-Florida State University
Groll, Nickolas-Florida State University
Hagen, Karl-Emory University
Hapanowicz, Rick-Cryogenic Limited
Harris, David-University of California-Berkeley
Harrison, Nicholas-STFC & Imperial College
London
Heutz, Sandrine-Imperial College London
Hicks, Robin-University of Victoria
Hill, Stephen-NHMFL and Florida State
University
Holmes, Stephen-University of MissouriSt.Louis
Kareis, Christopher-University of Utah
Kent, Andrew-New York University
Keramidas, Anastasios-University of Cyprus
Knowles, Elisabeth-University of Florida
Koo, Changhyun-University of Florida
Landee, Christopher-Clark University
Leznoff, Daniel-Simon Fraser University
Li, Chaoran-University of Florida
Liu, Junjie-University of Florida
Long, Jeffrey-University of California, Berkeley
Masunov, Artem-University of Central Florida
Meisel, Mark-University of Florida
Miller, Joel-University of Utah
Mucciolo, Eduardo-University of Central
Florida
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Mukherjee, Shreya-University of Florida
Musfeldt, Jan-University of Tennessee
Nguyen, Tu-University of Florida
Pantelides, Sokrates-Vanderbilt University
Papatriantafyllopoulou, Constantina-University
of Florida
Papavassiliou, Georgios- Institute of Materials
Science, NCSR
Pati, Mekhala-Florida State University
Perlepes, Spyros-University of Patras, Greece
Pham, Linh-University of Florida
Poole, Katye-University of Florida
Raptis, Raphael-University of Puerto Rico
Romero, Javier-University of Central Florida
Saber, Mohamed-Texas A&M University
Saha, Arpita-University of Florida
Sanakis, Ioannis-Institute of Materials Science,
NCSR
Sarachik, Myriam-City College of New York,
CUNY
Shatruk, Michael-Florida State University
Shultz, David-NC State University
Singh, Namrata-University of Florida
Soh, Yeong-Ah-Imperial College
Stamatatos, Theocharis-University of Patras,
Greece
Stamopoulos, Dennis-Institute of Materials
Science, NCSR
Strouse, Geoffrey-Florida State University
Subedi, Pradeep-New York University
Taguchi, Taketo-University of Florida
Talham, Dan-University of Florida
Tasiopoulos, Anastasio-University of Cyprus
Tejada, Javier-University of Barcelona
Thompson, Laurence-Memorial University
Tsukerblat, Boris-Ben-Gurion University of the
Negev
Turnbull, Mark-Clark University
Veige, Adam- University of Florida
Waldmann, Oliver-Physikalisches Institut,
Universitit Freiburg
Wen, Bo-City College of New York
Wernsdorfer, Wolfgang-Institut Neel, CNRS
TRANSPORTATION SERVICES
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ABSTRACTS
Listed alphabetically by the last name of
the presenting author
Mössbauer Spectroscopy Studies of Spin Transitions
in Polynuclear Iron Complexes
Catalina Achim
Carnegie Mellon University, Department of Chemistry, 4400 5th Ave., Pittsburgh, PA 15213
Email: achim@cmu.edu
Spin transition is a property of many Fe(II) complexes. While numerous mononuclear Fe(II)
complexes have been studied, there have been only a few studies of polynuclear Fe(II)
complexes that have this property. The latter complexes are very interesting because their study
may provide information relevant for the understanding of the interplay demonstrated in the case
of mononuclear complexes between weak interactions and the characteristics of the spin
transitions. This presentation will describe the results of variable temperature, variable field 57Fe
Mössbauer spectroscopy studies of polynuclear complexes that contain Fe(II) including
pentanuclear, trigonal bipyramid, heterometallic complexes and binuclear and tetranuclear
homometallic complexes and have a broad range of magnetic properties, including LS → HS
Fe(II) spin transitions (Figure 1a,b), charge transfer coupled spin transitions [1], and
ferromagnetic exchange coupling mediated by diamagnetic metal sites (Figure 1c).
Fe
Fe Fe
Fe Co Co
Fe
Cr
III
eII FeII
CrIII
Fe
FeII Fe Fe
Fe
FeIII
Fe
Co
NiII NiII
FeIII
Fe
FeIII
NiII ZnII ZnII
ZnII
FeIII
Co
Fe Fe Fe
Fe
Co
(a)
(b)
Figure. (a) Schematic representation of Fe3Fe2 and Fe3Co2 clusters; (b) Mössbauer spectra of Fe3Co2 at
4.2 K (top) and 300 K (bottom). The contributions from LS and HS FeII ions are represented by dashed (- -) and dotted (…) lines, respectively; (c) 1.5 K, 8 T Mössbauer spectrum of Fe3Cr2. The continuous line
is a simulation assuming no internal field at LS FeII; the dashed line for an internal field of 0.6 T. [1]
Hilfiger, M.G., Chen, M., Brinzari, T.V., Nocera, T.M., Shatruk, M.; Petasis, D.; Musfeldt, J.L.; Achim,
C., Dunbar, K.R. Angew. Chem., Intl. Ed., 2010, 49, 1410-3.
Old Ligands with New Coordination Chemistry: Unusual, High-Nuclearity
Manganese Clusters Bearing the Anions of 2-Pyridyl Oximes and Exhibiting
Interesting Magnetic Properties
Dimitris I. Alexandropoulos,*,a Constantina Papatriantafyllopoulou,b Manolis J. Manos,c
Anastasios J. Tasiopoulos,c Olivier Roubeau,d Simon J. Teat,e Guillem Aromi,f Spyros P.
Perlepes,a George Christou,b Theocharis C. Stamatatosa
a
Department of Chemistry, University of Patras, Patras 26500, Greece
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA
c
Department of Chemistry, University of Cyprus, 1678 Nicosia, Cyprus
d
Instituto de Ciencia de Materiales de Aragón, CSIC and Universidad de Zaragoza, Spain
e
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
f
Departament de Quimica Inorganica, Universitat de Barcelona, Spain
Email: thstama@chemistry.upatras.gr
b
The chances of identifying new high-spin MnIII-containing clusters and SMMs with
unprecedented structural motifs will benefit from the development of new reaction systems with
suitable organic ligands. A popular such family of ligands are the 2-pyridyl oximes. A large
number of polynuclear, homometallic Mn/2-pyridyl oximato complexes have been synthesized,
but unfortunately only few of them contain MnIII ions and behave as SMMs. We have now
discovered a simple synthetic route into high-nuclearity Mn/2-pyridyl oximato species, which
also possess interesting magnetic properties. In particular, the compounds described herein are
new examples of mixed-valence, MnII/III non-carboxylate species with unprecedented structural
motifs and rare nuclearities, which additionally exhibit appreciable ground state spin values.
On-chip SQUID Measurement of Quantum Tunneling of Molecular Spins in
High Fields
Lei Chen,* W. Wernsdorfer, Irinel Chiorescu
National High Magnetic Field Laboratory
1800 E. Paul Dirac Dr., Tallahassee, FL 32312, USA
Recent experiments involving molecular magnets [1] and diluted spin systems [2,3], show that
localized spins are highly promising candidates for future implementation of quantum computing
algorithms. On-chip spin detection schemes are desirable for studying such systems due to their
increased sensitivity. We implemented a method in which a small magnetic sample is placed in
the vicinity of a micron sized SQUID, thus allowing sensitive spin detection. Our setup at
NHMFL allows studies to be done in magnetic fields as high as 7 Tesla. Measurement of the
Landau-Zener quantum tunneling [4,5] in a swept magnetic field can provide us information
about magnetic molecules, like the anisotropy-induced tunneling gaps and entanglement of spin
states. In our experiments, the sample is placed close to the squid loop so that the spin magnetic
flux is well coupled to the SQUID magnetometer. Both the spins and the SQUID are seeing the
same controllable, uniform, external magnetic field. To be able to study a large family of
molecular magnets or diluted spin system, one needs to perform measurements in the presence of
as large fields as possible. Our on-chip SQUIDs are made of a thin layer of Nb, of only few
nanometers, and the magnetic field is aligned with high precision parallel to its plane, so that
SQUID superconductivity is preserved. Successful SQUID measurements of the quantum
tunneling of spins, in the presence of high fields up to 5.5T, will be presented. We conclude that
on-chip SQUID measurement technique allows observing fundamental quantum phenomena in
the presence of high magnetic field.
1. S. Bertaina et al, Nature 453, 203-208 (2008)
2. S. Nellutla et al, PRL. 99, 137601 (2007)
3. S. Bertaina et al, PRL 102, 050501 (2009)
4. W. Wernsdorfer et al, EPL 5, 552-558 (2000)
5. L. Chen et al, EPL 87 57010 (2009)
On-chip Methods to Study Low Temperature Magnetic and Superconducting
Samples
I. Chiorescu,* L. Chen, N. Groll
Department of Physics and the National High Magnetic Field Laboratory, Florida State
University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, U.S.A.
Email: ichiorescu@fsu.edu
In this talk I will discuss recent advancements in our laboratory that regards spin detection by onchip superconducting techniques. We have implemented a SQUID-based method, similar to one
used in Grenoble, able to measure spin systems in large magnetic fields. Also, microwave
transmission through an on-chip superconducting cavity and measured by a heterodyne system is
developed for the same purpose. Aside spin sensing these techniques demonstrate fine ability in
detecting properties of superconducting materials. Observation of the nonlinear Meissner effect
(NLME), a long-sought variety of the known Meissner effect, is demonstrated for the first time
as a function of magnetic field. NLME is observed in Nb films by measuring the resonance
frequency of a planar superconducting cavity as a function of the magnitude and the orientation
of a parallel magnetic field. Use of low power rf probing in films thinner than the London
penetration depth, significantly increases the field for the vortex penetration onset and enables
NLME detection under true equilibrium conditions. We propose to use NLME angular
spectroscopy to probe unconventional pairing symmetries in superconductors. The on-chip
cavity presented above is suitable for the study of nanosized magnetic samples as well, since it
allows spin resonance studies [2]; partial results will be discussed, as well as studies we have
performed with conventional ESR cavities.
[1] N. Groll, A. Gurevich, I. Chiorescu, “Measurement of the nonlinear Meissner effect in
superconducting Nb films using a resonant microwave cavity: A probe of unconventional pairing
symmetries”, arXiv: 0908.4097, Phys Rev B Rapid Comm., 2010, 81, 020504(R).
[2] S. Bertaina, L. Chen, N. Groll, J. Van Tol, N.S. Dalal, I. Chiorescu, “Multiphoton coherent
manipulation in large-spin qubits”, Phys. Rev. Letters, 2009, 102, 050501.
Some Recent Results in Manganese Cluster Chemistry and Single-Molecule
Magnetism
G. Christou,* Theocharis C. Stamatatos, C. Papatriantafyllopoulou, A. Saha
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA
Email: christou@chem.ufl.edu
The ability of single-molecule magnets (SMMs) to function as nanoscale magnetic particles at very low
temperatures has stimulated interest by inorganic chemists in the component properties on which this
phenomenon is based: high spin (S) ground states, and easy-axis magnetoanisotropy. Our work with
SMMs has been primarily concentrated in manganese cluster chemistry involving at least some JahnTeller distorted MnIII ions, the primary source to date of SMMs to date. As part of our efforts to prepare
and study new high spin molecules and SMMs, we continue to develop new synthetic methodologies,
and some recent results will be described. Two approaches will be emphasized: First, to vary the
peripheral organic ligation about the magnetic core in a way that fosters new metal topologies; and
second, to incorporate anisotropic lanthanide ions, or other heterometals, as a means of diverting Mn
chemistry away from its normal products towards new mixed-metal products with potentially
interesting magnetic properties. These approaches have both presented a variety of enjoyable synthetic
challenges, and have successfully led to satisfying developments and interesting new compounds that
will be presented in this talk.
Nanomechanics with Magnetic Molecules
Eugene M. Chudnovsky
Physics Department, CUNY Lehman College, Bronx, NY 10468-1589, U.S.A.
Email: Eugene.Chudnovsky@Lehman.CUNY.edu
Spin and rotational dynamics of magnetic molecules are coupled through conservation of the
total angular momentum. In a crystal this coupling dictates structure of spin-phonon interaction.
If the molecule is attached to a microcantilever (see Fig. 1 left), quantum oscillations of the spin
couple to the mechanical modes of the cantilever [1]. This effect can be detected by looking at
the splitting of the cantilever modes (Fig. 1 right).
Figure 1. (Color online) Left: Magnetic molecule on a microcantilever. Right: Computed splitting of the
cantilever mode versus tunnel splitting Δ and frequency of the ac magnetic field ω.
One can also induce a Landau-Zener spin reversal in the magnetic molecule by applying a pulse
of the magnetic field. When the molecule is bridged between conducting leads (see Fig. 2), the
Landau-Zener transition results in the oscillating mechanical torque that causes rotational
vibrations of the molecule [2]. They can be detected by measuring oscillations of the tunneling
current through the molecule.
Figure 2. (Color online) Magnetic molecule bridged between conducting leads. Spin transitions generate
mechanical torque that affects the tunneling electronic current through the molecule.
[1] R. Jaafar and E. M. Chudnovsky, Phys. Rev. Lett. 102, 227202 (2009).
[2] R. Jaafar, E. M. Chudnovsky, and D. A. Garanin, Europhys. Lett. 89, 27001 (2010).
Quantum Coherent Properties of Mononuclear Lanthanide-based
Single-Molecule Magnets
S. Datta,*1 S. Ghosh,1 J. van Tol,1 J. Krzystek,1 S. Hill,1
E.del Barco,2 S. Cardon-Serra3 and E. Coronado3
1
NHMFL and Department of Physics, FSU, Tallahassee, FL, USA
2
Department of Physics, University of Central Florida, Orlando, FL, USA
3
Instituto deCiencio Molecular, Universidad de Valencia, Spain
Email: sdatta@magnet.fsu.edu
We report measurements of the longitudinal and transverse relaxation times of diluted single crystals of
recently discovered mononuclear holmium based single-molecule magnets (SMMs), encapsulated in
polyoxometallate cages [1].
The encapsulation offers the potential for possible usage in molecular
spintronic devices as it preserves the bulk SMM properties outside of the crystal. Magnetic anisotropy in
these complexes originates from the splitting of J ground state in presence of a ligand field. At low
frequencies only the hyperfine transitions between the lowest
±mJ ground state doublet are observed. The results are compared for different hyperfine transitions and
crystal dilutions. Observation of clear Rabi oscillations indicates one can manipulate the spin coherently
in these complexes.
[1] AlDamen et al.,JACS, 2008, 130, 8874-8875.
.
Nanospintronics with Molecular Magnets
E. del Barco1,* F. Haque1, M. Langhirt1, T. Taguchi2, and G. Christou2
1
2
Department of Physics, University of Central Florida, Orlando, FL 32816, USA
Department of Chemistry, University of Florida, Gainesville, Florida 32611 USA
Email: delbarco@physics.ucf.edu
I will discuss our current project and future prospects of the study of individual molecular
nanomagnets by means of single-electron transport experiments. As an example, I will present
some recent results on a Mn4 single-molecule magnet (SMM) in where amino groups were added
to electrically protect the magnetic core and to increase the stability of the molecule when
deposited on a single-electron transistor (SET) device. Experiments were conducted at
temperatures down to 230mK in the presence of high magnetic fields applied at different
directions with respect to the SET geometry. We have observed Coulomb blockade an electronic
excitations that curve with the magnetic field and present zero-field splitting, constituting
evidence of magnetic anisotropy. Avoided level crossings and large excitations slopes are
associated with the quantum behavior of with high spin (S ~ 9) molecular states.
Figure 1. (Color online) Low temperature (230 mK) Single-electron current (A) and differential
conductance (B, C) through an individual Mn4 single-molecule magnet. The magnetic field dependence of
the molecular transport excitations evidence curvatures and avoided level crossing associated to zero-field
splitting anisotropy and quantum superposition of spin projection levels.
DNA Modified Gadolinium Phosphate Nanoparticles as
MRI Contrast Agents
Matthieu F. Dumont,1* Celine Baligand2, Maria de Castro2,
Glenn A. Walter2 and Daniel R.Talham1
1
Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA. 2Department of
Physiology and Functional Genomic, University of Florida, Gainesville, FL 32610, USA.
Email: dumont@ufl.edu
Gadolinium (3+), S=7/2, induces very high nuclear relaxivity of surrounding water molecules making it
very effective as a contrast agent in magnetic resonance imaging. However, there are recent concerns
about the decomplexation of commercial chelates releasing toxic Gd3+ cations. We are exploring the
surface modification of inorganic coordination polymers where Gd3+ is coordinated to phosphate
ligands, reasoning that this framework should be stable in biological conditions. Gadolinium phosphate
nanoparticles have been synthesized and we have demonstrated facile DNA functionalization of the
surfaces. Fluorescence data show that Gd3+ at the surface of the particle has an essential role in
stabilizing the specific binding of the DNA to the surface of the particle. Magnetic resonance relaxivity
measurements were collected at 600 and 750 MHz. MRI data suggest that the biofunctionalized
gadolinium phosphate particles are viable contrast agents.
B
C
O
H
O
P
OO
O
P
OO
O
c
3+ Gd3+ Gd3+ Gd3+ Gd3+ Gd3+
GdO
O O O OO O OO O O O O OO
P
P
P
P
P
GdPO4
b
a
O
A
d
f
e
(A) HRTEM images of the functionalized gadolinium phosphate nanoparticles, (B) Scheme describing the
specific binding of the phosphorylated DNA on the Gd surface (C) T2-Weighted MR image of
nanoparticle dilution (concentration decreasing from b to e). Omniscan (a) and nanopure water (f). All
suspensions are in 0.5% agarose.
Engendering Bistability in Cyanide Magnetic Materials
Kim R. Dunbar,* Carolina Avendano, Matthew Hilfiger, Andrey Prosvirin, Xinyi Wang
Department of Chemistry, Texas A&M University, College Staion,Texas USA
Email: dunbar@mail.chem.tamu.edu
A great deal of interest in current research is focused on materials at the interface between
macroscopic and microscopic realms. Research activity in molecular magnetic and conducting
materials falls under the natural umbrella of this current trend. A traditional method for obtaining
magnetic materials at the nanoscale level is by the mechanical preparation of small magnetic
particles by the “Top-Down” approach but this method is limited by the inherent non-uniform
size distribution of nanoparticles. The fascination with magnetism in confinement has led to a
growing emphasis on the preparation of materials via solution methods that take advantage of the
intrinsic chemical and geometrical properties of a molecule for the design of magnetic
compounds. In this vein we are targeting magnetic architectures that involve transition metal ions
bridged by the cyanide anion. Although the examples are still far fewer than those in the oxide
family, the observation of bistability in the form of SMM behavior for cyanide clusters has
sparked high interest in many groups worldwide. Other approaches to realizing switchable
magnetic properties involve the study of molecules or extended phases that respond to changes in
temperature or light irradiation (e.g., Spin-Crossover, Charge transfer Induced Spin Transitions)
and alterations in interstitial solvent/water content and supramolecular interactions. In our group
we are actively engaged in the aforementioned activities which involve the use of various
cyanometallates, including those of 4d and 5d metal ions, to explore the possibilities for
improved exchange interactions and enhanced anisotropy. Our recent findings will be presented
which include a record ground state molecule for a docosanuclear cluster obtained from a
reaction of the heptacyanomolybdate(III) anion with a Mn(II) precursor.
Molecular Nanomagnets in the Weak Exchange Limit
F. El Hallak1,2, J. van Slageren2,3, P. Rosa4, M. Dressel2
1
London Centre for Nanotechnology, University College London, United Kingdom
2
3
4
1. Physikalisches Institut, University of Stuttgart, Germany
School of Chemistry, University of Nottingham, United Kingdom
Institut de Chimie de la Matiére Condensée de Bordeaux – CNRS, France
Email: f.hallak@ucl.ac.uk
Two decades of research on molecular nanomagnets have demonstrated that these systems
display a rich variety of fascinating quantum phenomena, including quantum tunneling of the
magnetization, quantum tunneling of the Néel vector, and quantum coherence. The vast majority
of detailed physical investigations were performed on systems where the isotropic exchange
interaction is strong compared to other interactions in the system, such as single-ion anisotropies,
non-Heisenberg spin-spin interactions, or the Zeeman interaction. We have studied a Fe2
molecular nanomagnet that displays a single giant step in magnetization (Figure 1). We present
detailed susceptibility and torque magnetometry investigations which illustrate that in this
system the single-ion anisotropy is dominant over the isotropic exchange coupling. The
theoretical analysis revealed that this molecule is a very promising candidate for the direct
observation of the Néel vector tunnel splitting in weakly coupled molecular nanomagnets.
Figure. (Color online) Magnetization of the Fe2 system plotted vs field for different D/J values. For
D/J>0.5, a single step in the magnetization occurs which is consistent with a change in the spin state
from Sz = 0 to Sz = -4.
Molecule-based Diruthenium Magnet with Interpenetrating Sublattices
R.S. Fishman,1* S. Okamoto1, W.W. Shum2,3, and J.S. Miller2
1
2
Oak Ridge National Laboratory, Oak Ridge, TN 37831
Chemistry Department, University of Utah, Salt Lake City, UT 84112
3
Department of Chemistry, Cornell University, Ithaca, NY 14853
Email: fishmanrs@ornl.gov
The molecule-based magnet [Ru2(O2CMe)4]3[Cr(CN)6] contains two interpenetrating cubic
sublattices.
Each sublattice is magnetically frustrated by the easy-plane anisotropy of the
spin-3/2 diruthenium paddlewheel complexes, which lie at the middle of each cube edge and
are antiferromagnetically coupled by the exchange interaction J c ~ 1.7 meV to spin-3/2 Cr
ions at the cube corners. Consequently, each cubic sublattice has a non-collinear spin state
with net moment along one of the cubic diagonals. The moments of the two interpenetrating
sublattices behave like giant moments that are antiferromagnetically coupled at small fields
and become aligned above a critical field of about 1000 Oe ~ Kc/B, where Kc ~ 2 x 10-3
meV is the weak coupling between sublattices. Because the sublattice spin configurations
only weakly depend on field in the range of the experimental measurements, the magnetic
correlation length can be directly estimated from fits to the field and temperature
dependence of the magnetization while a polycrystalline sample undergoes a metamagnetic
transition [1,2]. The fitting parameters change dramatically at a pressure of about 8 kbar,
which may signal a high- (S = 3/2) to low-spin (S = 1/2) transition on the diruthenium
complex. Research sponsored by NSF grant 0553573 and by the Division of Materials
Sciences and Engineering, U.S. Department of Energy under contract with UT-Battelle,
LLC.
[1] R.S. Fishman, S. Okamoto, W.W. Shum, and J.S. Miller, Physical Review B 2009, 80,
064401.
[2] R.S. Fishman, S. Okamoto, and J.S. Miller, Physical Review B 2009, 80, 140416(R).
Collective Coupling of ~1016 Fe8 Single-Molecule Magnets to a Resonant Cavity
Jonathan R. Friedman,* A. W. Eddins
Department of Physics, Amherst College, Amherst, MA 01002, USA
C. C. Beedle, D. N. Hendrickson
Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California
92093, USA
Email: jrfriedman@amherst.edu
When a spin resonantly couples to the electromagnetic mode of a cavity, spin and photon states
hybridize producing entangled states and a “vacuum Rabi splitting” between the states. The magneticdipole coupling between these entangled states results in a splitting of 13 s-1, i.e. practically
immeasurable. A well-known model [1] predicts that for N spins coupled to a cavity, the vacuum Rabi
splitting is enhanced by
N . We performed a low-temperature reflection spectroscopy experiment on
a single crystal of the Fe8 single-molecule magnet (SMM) in a cylindrical cavity mode of bare frequency
147.6 GHz. An applied magnetic field brings the SMMs to resonance with this mode, resulting in an
observed splitting at 1.75 K of 3.4  109 s-1. This value corresponds to ~7  1016 Fe8 SMMs collectively
coupled to the cavity. From the dimensions of the crystal, we estimate a total of 6  1016 SMMs in the
sample, i.e. essentially all of the crystal’s molecules are simultaneously coupled to the cavity. The
number of coupled spins N can be controlled by changing the sample temperature; we find that the
value of N deduced from our measurements tracks with the thermal population in the SMM’s spin
ground state.
Figure. Absorbed microwave power as a function of magnetic field and frequency.
[1] M. Tavis and F. W. Cummings, Phys. Rev., 1968, 170, 379
Collective Relaxation of Magnetization in Magnetic Molecular Solids at T = 0
Anupam Garg
Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208, USA
Email: agarg@northwestern.edu
The quantum mechanical dynamics at the single molecule level are well understood in many magnetic
molecular solids. This is especially so in systems where the phenomenon of gap oscillations is seen. In
contrast, the dynamics at the many molecule level, i.e., of the magnetization of a bulk solid are much less
well understood, and there is a wealth of experimental data (square-root-in-time dependence at short
times, nonexponential slow relaxation at long times, hole digging, etc.) for which the theory is much less
complete. We will present two aspects of our work on this problem: (1) a careful influence functional
calculation of the effects of coupling to nuclear spins and other molecular spins, which explains how the
quantum tunneling dynamics changes from coherent to incoherent [1]. (2) a study of the resulting
classical problem, which is like a long-ranged Glauber model, in which the individual molecular spins
relax in the dipolar field of the other molecular spins. We will present results from numerical simulations,
as well as well as a theoretical approach wherein we attempt to reduce the dynamics to a system of rate
equations. The advantages and shortcomings of this approach will be discussed, along with a long list of
open problems.
[1] Avinash Vijayaraghavan and A. Garg, Phys. Rev. B, 2009, 79, 104423.
High Field Measurements of Superconducting Cavities for Implementation
with Magnetic Spin Systems
N. Groll,* A. Gurevich, I. Chiorescu
National High Magnetic Field Laboratory
1800 E. Paul Dirac Dr., Tallahassee, FL 32312, USA
Email: groll@magnet.fsu.edu
On-chip superconducting cavities offer a controllable electro-magnetic environment
which can be used to study and manipulate quantum spins. In principle, any number of photons
can be added in such cavity and study the spin-photon entanglement [1]. We studied the
possibility of using a superconducting cavity in a high planar magnetic field and found direct
evidence of the nonlinear Meissner effect. The Meissner effect is one of the fundamental
manifestations of macroscopic phase coherence of a superconducting (SC) state. At high fields,
the superfluid density is dependent on the velocity of the condensate resulting in the NLME [2,
3]. We report observation of the NLME in Nb films by measuring the resonance frequency of a
planar SC cavity as a function of the magnitude and the orientation of a parallel magnetic field
[4]. Using low power rf probing in films thinner than the London penetration depth significantly
increases the field for the vortex penetration onset and enables NLME detection under true
equilibrium conditions. The data agree very well with calculations based on the Usadel
equations. We propose to use the high field measurement capabilities to study magnetic spin
systems coupled to superconducting resonators at millikelvin temperatures.
[1] I. Chiorescu, N. Groll, S. Bertaina, T. Mori, S. Myiashita, submitted. arXiv:1004.3605
[2] S.K. Yip and J.A. Sauls, PRL 69, 2264 (1992)
[3] R. Prozorov and R.W. Giannetta, Supercond. Sci. Technol. 19, R41(2006).
[4] N. Groll, A. Gurevich, I. Chiorescu, Phys. Rev. B Rapid Commun., 81, 020504(R) (2010)
Ferrimagnetic Mixed-Valence and Mixed-Metal Formate Analogues of Prussian
Blue
Karl S. Hagen,*,1 S. G. Naik,2 B. H. Huynh,2 A.Maselo,3 and G. Christou3
Departments of Chemistry1 and Physics 2, Emory University, Atlanta, GA, 30322, USA
Department of Chemistry,3 University of Florida, Gainesville, FL, 32611, USA
Email: khagen@emory.edu
A single crystal contains long-range order, but this regularity in structure can be lost when it consists of a
mixture of closely related building units, as in the metal organic framework structures of di- and
trivalent transition metal formates, [M(HCOO)3]-1,0. We have prepared large crystals of ordered 3D
framework metal formates (Me2NH2)[MIIFeIII(HCO2)6] (M = Fe) [1] that exhibit negative magnetization
analogous to that observed in the ground-breaking mixed-valence layered oxalates, A[FeIIFeIII(C2O4)3].[2]
We extend this work to mixed-metal structures (M = Mn, Co, and Ni) as well as new FeII-rich materials
(Me2NH2)n[(FeII)nFeIII(HCO2)3(n+1)] (n = 2, and 4) where layers of FeII separate layers of mixed-valence FeII
and FeIII.
Figure. (Color online) 3D framework structures
of MII and FeIII linked by formates in a
hexagonal cell with the c-axis vertical.
[1] Karl S. Hagen, S. G. Naik, B. H. Huynh, A.Maselo, and G. Christou, J. Am. Chem. Soc., 2009, 131, 75167517.
[2] Mathonière, C.; Nuttall, C. J.; Carling, S. G.; Day, P. Inorg. Chem. 1996, 35, 1201-1206.
Magnetic Chain Compounds Incorporating [ReCl4(CN)2]2D. Harris,* M. Bennett, C. Coulon, R. Clérac, J. Long
Department of Chemistry, University of California, Berkeley, CA 94720, USA
CNRS, UPR 8641, Centre de Recherche Paul Pascal (CRPP), Equipe "Matériaux Moléculaires
Magnétiques", 115 avenue du Dr. Albert Schweitzer, Pessac, F-33600, France
Email: dharris@berkeley.edu
Less than a decade ago, slow relaxation of the magnetization was discovered in one-dimensional
coordination solids. These solids, known as single-chain magnets, often display spin-reversal
barriers considerably higher than do their single-molecule magnet counterparts, thus
demonstrating their potential in practical applications such as high-density information storage.
Toward this end, we have employed a building block approach to assemble new single-chain
magnets from mononuclear transition metal complexes that feature axial terminal cyanide
ligands, which can bridge other metal ions to direct the formation of one-dimensional solids.
This strategy has led to the formation of the S = 3/2, high-anisotropy complex [ReCl4(CN)2]2-, the
first example of a paramagnetic molecule of the form [MXx(CN)y]n-. We have successfully
incorporated
this
building
unit
into
a
series
of
chain
compounds
of
formulae
[(DMF)4MReCl4(CN)2] (M = Mn, Fe, Co, Ni) that display slow relaxation of the magnetization
at low temperature.1 In addition, we have begun targeting chain compounds wherein
[ReCl4(CN)2]2- units are bridged via CuII centers as a means to install strong intrachain
ferromagnetic coupling. This effort stems from the observation that M-CN-CuII exchange
interactions are often considerably stronger than those of other first-row metals, owing to the
presence of a single electron residing in a dx -y orbital, along the direction of exchange coupling
2
2
through the cyanide ligand. Toward this end, we have isolated the zig-zag chain compound
(Bu4N)[TpCuReCl4(CN)2], which demonstrates extremely strong ferromagnetic exchange (J =
+28 cm-1) between CuII and ReIV centers and metamagnetic behavior at low temperature.2
[1] Harris, T. D.; Bennett, M. V.; Clérac, R.; Long, J. R. J. Am. Chem. Soc. 2010, 132, 3980.
[2] Harris, T. D.; Coulon, C.; Clérac, R.; Long, J. R. submitted.
Localised and Itinerate Magnetism in TM (TCNE)2: A Theoretical
Perspective
Nicholas M Harrison,* 1,2 Giulia C de Fusco1, Barbara Montanari2
1
Thomas Young Centre, Department of Chemistry, Imperial College London, SW7 2AZ, UK
2
Computational Materials Science Group, STFC Rutherford Appleton Laboratory, Chilton,
Didcot, Oxon, OX11 0QX, UK
Email: nicholas.harrison@imperial.ac.uk
The electronic and magnetic structure of a M(TCNE)2 for M=Ti, V, Cr, Mn, Fe, Co, Ni and Nb is
studied using hybrid exchange density functional theory based on a putative crystal structure
which is consistent with the observed local structure of the V material. The observed strong
magnetic coupling in the V case is reproduced and a mechanism for the stability of the insulating
state and strong exchange coupling suggested [1].
Figure. (Color online) Nb(TCNE)2
A simple Hubbard-Anderson model is introduced and parameterized to provide a general
description of the trends in the correlated electronic structure across the series.
[1] De Fusco GC, Pisani L, Montanari B, Harrison, N M, Density functional study of the
magnetic coupling in V(TCNE)2, Phys. Rev. B, 2009, 79, 085201
Influence of Transition Metals and Structure in
Magnetism of Molecular Thin Films
S. Heutz 1, *, Z. Wu 1, M. Serri 1, S. Felton 1, G. Aeppli 2, W. Wu2, A. J. Fisher2
Department of Materials and London Centre for Nanotechnology, Imperial College London, UK
Department of Physics and London Centre for Nanotechnology, University College London, UK
Email: s.heutz@imperial.ac.uk
Phthalocyanines are polyaromatic molecules that can accommodate a variety of species in their central
cavity. They can be easily deposited as thin films, and are important components of molecular
optoelectronic devices. Magnetic couplings have already been observed in single crystals for several
decades [1], but until recent work in our group [2], assessment in more technologically thin film form
has been more problematic.
Here we will present the magnetic properties in flexible phthalocyanine thin films deposited using
different sublimation techniques, leading to a range of structural polymorphs and structures. Within
isostructural series, the central divalent transition metals can give rise to vastly different magnetic
couplings, in turn ferro-, antiferro- or paramagnetic. The importance of intermolecular geometry and
anisotropy will also be addressed.
[1] C. G. Barraclough et al., J. Chem. Phys., 1970, 53, 1638.
[2] S. Heutz et al., Adv. Mater., 2007, 19, 3618.
Spin and Charge Transfer in Ruthenium Complexes of Verdazyl Radicals
Robin G. Hicks,*a Stephen D.J. McKinnon,a and A. Barry P. Leverb
a
Department of Chemistry, University of Victoria, Victoria, B.C. Canada
b
Department of Chemistry, York University, Toronto, Ontario, Canada
rhicks@uvic.ca
The coordination chemistry of verdazyl radicals 1 has been developing steadily over the past
decade. The principal motivation behind these studies has been to examine intramolecular
magnetic exchange phenomena, the results of which have highlighted verdazyls as new spinbearing building blocks for the metal-radical approach to new magnetic materials. However, the
redox properties of metal-verdazyl complexes, or even of free verdazyls themselves, have been
largely unexplored. Given the many interesting chemical and physical properties associated with
other kinds of redox-active (“non-innocent”) ligands (e.g. dioxolenes, dithiolenes, phenoxyls,
etc.), we have begun to explore metal-verdazyl complexes in this context. This presentation will
focus on our recent investigations of several classes of verdazyl complexes of ruthenium (2),
highlighting the non-innocent nature of the verdazyl ligand and its implications for the chemical
and physical properties of these sorts of complexes.
O
O
R
N
N
N
N
R
N
N
N
N
[Ru]
R'
1
N
2
The Effective Barrier to Magnetization Reversal in Mn12 Single-Molecule Magnets
Stephen Hill,1 * Gage Redler,2 Saiti Datta,1 Christos Lampropoulos3 and George Christou3
1
2
3
NHMFL and Department of Physics, FSU, Tallahassee, FL32310 USA
Department of Physics, University of Florida, Gainesville FL32611 USA
Department of Chemistry, University of Florida, Gainesville FL32611 USA
Email: shill@magnet.fsu.edu
Single-molecule magnets (SMMs) consist of a core of exchange-coupled transition metal ions
that collectively possess a large magnetic moment per molecule and a sizable magnetic
anisotropy barrier, U, separating ‘up’ and ‘down’ spin projections. Crystals containing ordered
arrays of SMMs exhibit magnetic hysteresis below a characteristic blocking temperature, TB.
This hysteresis can be attributed to a bistability at the single-molecule level resulting from the
anisotropy barrier. Nevertheless, the low-temperature (T < TB) magnetization dynamics observed
in many SMM crystals is dramatically influenced by quantum effects that can give rise to
tunneling of a molecule’s magnetic moment through the anisotropy barrier. This tunneling often
results in an effective barrier, Ueff, which is significantly reduced in comparison to the
spectroscopic barrier inferred from considerations of the total spin and axial anisotropy
associated with the SMM [1]. We compare values of Ueff deduced from thermodynamic
measurements (AC susceptibility) with spectroscopic barriers determined from high-frequency
electron paramagnetic resonance (HFEPR) for a wide variety of Mn12 SMMs [1-4]. These
comparisons reveal important insights into the factors that influence the values of Ueff reported
on the basis of AC susceptibility measurements. In particular, for very high-symmetry SMMs,
sample-to-sample variations in Ueff can be correlated with the degree of disorder in a crystal
which, in turn, may depend on sample preparation [2]. We also observe deviations from simple
Arrhenius behavior which clearly influences the value of Ueff determined from AC studies
performed over different frequency intervals [4]. Meanwhile, HFEPR provides important
spectroscopic signatures of the quantum tunneling interactions that influence Ueff [1, 2].
[1]
[2]
[3]
[4]
Hill et al., Phys. Rev. B 80, 174416 (2009).
Redler et al., Phys. Rev. B 80, 094408 (2009).
Lampropoulos et al., Inorg. Chem. 49, 1325 (2010).
Lampropoulos et al., Eur. J. Chem. Phys. Phys. Chem. 10, 2397 (2009).
Tuning Magnetic and Optical Bistability in Tetranuclear Cyanometalates
S. M. Holmes,* R. Clérac, C. Mathonière, Y.-Z. Zhang, D. Li, M. Kalisz
Department of Chemistry & Biochemistry, University of Missouri-St. Louis, St. Louis, USA, Key
Laboratory of Pesticide and Chemical Biology of Ministry of Education, College of Chemistry,
Central China Normal University, Wuhan, China, CNRS, UPR 8641, Centre de Recherche Paul
Pascal (CRPP), Equipe “Matériaux Moléculaires Magnétiques”, Pessac, France, Université de
Bordeaux, UPR 8641, Pessac, France, CNRS, Université de Bordeuax, Institut de Chimie de la
Matière Condensée de Bordeaux, Pessac, France
Email: holmesst@umsl.edu
Over the last decade there has been considerable interest in the development of tunable
molecule-based materials that exhibit changes in their optical and magnetic properties as a
function of external stimuli; Co/Fe Prussian blue analogues are the best characterized examples
of such materials. These network solids exhibit optical and magnetic bistability that is ascribed to
the conversion of FeII-CN-CoIII into FeIII-CN-CoII units via electron transfer coupled spin state
changes. We previously reported that polynuclear complexes containing Fe(-CN)Co linkages
can be engineered via the self-assembly of cyanometalate anions and coordinatively unsaturated
transition metal cations. These complexes mimic the thermally- and photo-induced bistability
behavior seen for many Co/Fe Prussian blues, with long lifetimes ( ~ 10 y at 120 K) observed
for octanuclear {Fe4Co4} complexes. This seminar will discuss recent efforts directed at tuning
the magnetic and optical properties of {Fe2Co2} analogues from a structure-property standpoint.
Figure 1.T vs T data for 1 before (●) and after irradiation (●). Inset: X-ray structure of 1 at 230 K.
Magnetically Ordered Non-Prussian Blue Structured Prussian Blue
Analogues
Christopher M. Kareis,*,† Joshua G. Moore,† Kil Sik Min,†,£ Jong-Won Park,† Garima Bali,†
Bretni S. Kennon,† Joel S. Miller,† Jae-Hyuk Her,‡,€ and Peter W. Stephens‡
†
Department of Chemistry, 315 S. 1400 E. RM 2124, University of Utah, Salt Lake City, Utah
84112-0850 and ‡Department of Physics & Astronomy, Stony Brook University, Stony Brook,
New York 11794-3800. €Current address: GE Global Research, 1 Research Circle, Niskayuna,
NY 12309. £Current address: Department of Chemistry Education, Kyungpook National
University, Daegu, South Korea
Email: ckareis@chem.utah.edu
New non-Prussian blue structured Prussian blue analogues formed from the reaction of
Mn(O2CCH3)2 with A-CN (A = Na, K, Rb, Cs, Et4N) in aqueous and non-aqueous media is
discussed. The reaction of the alkali metal cyanides with MnII formed A2Mn[Mn(CN)6] (A = K,
Rb, Cs) and Na2Mn[Mn(CN)6]•2H2O which can be dehydrated to form Na2Mn[Mn(CN)6].
A2Mn[Mn(CN)6] (A = K, Rb) do not exhibit the face centered cubic structure expected for
Prussian blue structured materials. The linearity of the Mn-N≡C bonds increase as the size of the
alkali metal cation increases [148.8o (K+) > 153.3o (Rb+) > 180o (Cs+)] directly effecting the
magnetic ordering temperature, Tc [Na+ (~60 K) > K+ (41 K) > Rb+ (34.6 K) > Cs+ (21 K)].
Increasing the size of the cation to Et4N+ yielded a new Prussian blue analog of
(NEt4)2Mn3(CN)8 composition that exhibits an unprecedented layered (2-D) structure with both
octahedral and tetrahedral MnII sites. This material orders as a ferrimagnet. When the reaction is
carried out in methanol (NEt4)Mn3(CN)7 forms in which the 2-D layers similar to that observed
for (NEt4)2Mn3(CN)8 are bridged through the MnII tetrahedral sites forming a 3-D structure. The
bridging leads to strong direct antiferromagnetic coupling and an antiferromagnetic ground state.
These structure and magnetic properties will be discussed.
p-Semiquinone and Hydroquinone Bridged V(IV/V) Complexes: Structure,
Magnetic and Spectroscopic Properties
A. D. Keramidas,a* C. Drouza,b M. Stylianoua
a
b
Department of Chemistry, University of Cyprus,1678 Nicosia, Cyprus
Department of Agriculture Production, Biotechnology and Food Science, Cyprus University of
Technology, 3603, Limassol, Cyprus
Email: akeramid@ucy.ac.cy
The investigation of the association between the electron and proton transfer in the metal ion -
hydroquinone/semiquinone/quinone interacting systems is particularly important in order to
understand the factors which regulate the redox potentials and the pathways in electron transfer
reactions between transition metal centers and p-semiquinone radicals. Our focus in this work is
on the synthesis and characterization in solid state and solution of stable complexes of V IV/VV
with p-semiquinonate radicals as well as the investigation of the H+ induced electron transfer
between the metal centers and the coordinated semiquinonate/hydroquinonate ligands.
Substituted hydroquinones with chelate groups (Scheme 1) were used to stabilize vanadium
complexes. The VIV/VV – semiquinonate/hydroquinonate, hexanuclear, tetranuclear and
dinuclear species were isolated and characterized in solid state by X-ray crystallography. UVVis and NMR spectroscopies, electrochemistry and magnetism were employed for the
investigation of the speciation, redox and magnetic properties of these complexes.
Scheme 1. Hydroquinone ligands.
Acknowledgements: The authors would like to thank PRF of Cyprus (TEXNO/0506/19) for their
financial support.
Neutron Scattering from a Photomagnetic Cobalt Hexacyanoferrate
Prussian Blue Analogue§
E. S. Knowles,*,a D. M. Pajerowskia, M. J. Andrusb, M. F. Dumontb, , J. E. Gardnerb,
V. O. Garleac, J. L. Zaretskyc,d, G. E. Granrothc, S. E. Naglerc, D. R. Talhamb, M. W. Meisela
a
Department of Physics and NHMFL, University of Florida, Gainesville, FL 32611-8440, USA
b
Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
c
d
Neutron Scattering Sciences Division, ORNL, Oak Ridge, TN 37831-6477, USA
Ames Laboratory, Department of Physics, Iowa State University, Ames, IA 50011, USA
Email: meisel@phys.ufl.edu
Our group has been applying neutron scattering techniques to the molecule based
K0.2Co1.4[Fe(CN)6]6.9H2O Prussian blue analogue (Figure 1 (a)) that displays photoinduced
magnetization [1].
Single-ion excitations and ligand field multiplet calculations, structural
transitions induced by temperature and light, and magnetic structure refinements comparing
ferromagnetic and antiferromagnetic superexchange will be presented for powders of
K0.2Co[Fe(CN)6]·nD2O, Figure 1 (b).
These neutron scattering data, which provide
microscopic information, will then be connected back to the well documented macroscopic
magnetic properties.
(a)
(b)
Figure 1. (Color Online) (a) An idealized representation of the K0.2Co[Fe(CN)6]0.7·nD2O
unit cell. (b) A schematic of the low-energy splitting of the ions, starting with the ligand
field ground states.
1. O. Sato, T. Iyoda, A. Fujishima, and K. Hashimoto, Science 272 (1996) 704.
§ This work was supported, in part, by NSF DMR-071400 (MWM), NSF DMR-0543362
(DRT), NSF DMR-0654118 (NHMFL), and the State of Florida. ORNL is managed by
UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725.
Magnetic Properties of a Second Generation 2D Copper Antiferromagnet,
[Cu(pz)2(2-pyone)2](ClO4)2
C. P. Landee,* F. Xiao, V. Selmani, and M. M. Turnbull
Department of Physics and Carlson School of Chemistry, Clark University
Worcester, MA 01610 (USA)
Email:clandee@clarku.edu
Antiferromagnetic compounds consisting of pyrazine-bridged Cu(II) layers separated (Cu(pz)2(ClO4)2 [1])
or linked by anions ([Cu(pz)2HF2](PF6) [2]) have recently been used to examine the influence of interlayer
exchange (J´) and exchange anisotropy () upon the 3D ordering process within quasi-2D Heisenberg
antiferromagnets which, in principle, order only at T = 0. In an effort to produce antiferromagnetic
layers with even greater isolation, we have synthesized the title compound 1 for which 2-pyone = 2pyridone.
In 1 (Fig. 1), the axial sites of the copper atom
are occupied by pyridone oxygens, with the
rest of the molecule projecting between the
layers. The Cu-Cu distance between adjacent
layers has been dramatically increased from 7.9
Å in Cu(pz)2(ClO4)2 to 13.1 Å in 1. We will report
on the structure and magnetic properties of the
title compound.
Figure 1. (Color online) Crystal structure of 1,
viewed parallel to the copper-pyrazine planes.
Cu-light blue, N-dark blue, O-red, Cl-green.
[1] F. Xiao et al, Phys. Rev. B 2009 79, 134412.
[2] P. A. Goddard et al, New J. of Physics 2008
10, 083205.
Magnetic Properties of Cyanoaurate-based Coordination Polymer Materials
Probed by Magnetometry and Muon Spin Resonance
Daniel B. Leznoff
Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, B.C. V5A1S6 CANADA
Email: dleznoff@sfu.ca
Cyanometallate coordination polymers have a distinguished history in molecule-based magnetism
research, starting with the prototypical Prussian Blue-type materials. Most cyanometallate polymers
use octahedral or square-planar building blocks. In comparison, we have been exploring neglected
linear d10-[M(CN)2]- building blocks (M=Au,Ag) in coordination polymers to take advantage of attractive
metallophilic interactions to increase structural dimensionality.[1] Simple ligand-free "mineral-like"
cyanoaurate(I)-based polymers of the form M[Au(CN)2]2(H2O)x (M=Mn-Cu) have unprecedented aquabridged metal chain structures (see Figure below);[2] their magnetic behaviour changes as a function of
metal cation and data indicates that, overall, water is a surprisingly weak mediator of magnetic
exchange compared with hydroxo or oxo-bridges. The structures and magnetic properties change
drastically upon dehydration to M[Au(CN)2]2 systems. Analogous ligand-free polymers based on the
square-planar d8 [Au(CN)4]- building block and their magnetic properties will also be presented. Use of
the TRIUMF cyclotron's muon-spin resonance facility to detect magnetic
order or spin-freezing phase transitions in all these systems will also be
detailed,[2] as well as a related cautionary tale about materials properties
of products obtained from hydrothermal synthesis.[3]
Figure. (Colour online) Structural motif of M(-OH2)2[Au(CN)2]2 (M = Mn,
Fe, Co, Ni, Cu) showing a chain formed by double aqua-bridges.
[1] Inorg. Chem., 2001, 40, 6026; Chem. Soc. Rev., 2008, 37, 1884. [2] Chem. Eur. J., 2006, 12, 6748;
Inorg. Chem., 2009, 48, 55. [3] Chem. Eur. J., 2008, 14, 7156.
Applications of Coordination Chemistry in the Synthesis of New
Single-Molecule and Single-Chain Magnets
T. David Harris, Jeffrey D. Rinehart, Danna E. Freedman, Joseph M. Zadrozny,
Katie R. Meihaus, Xiaowen Feng, Pierre Dechambenoit, Bettina Bechlars,
Deanna M. D’Alessandro, David M. Jenkins, and Jeffrey R. Long*
Department of Chemistry, University of California, Berkeley, CA 94720 USA
Email: jrlong@berkeley.edu
In an effort to produce new examples of single-molecule and single-chain magnets, we are
exploring routes to mononuclear complexes with a large magnetic anisotropy and their
incorporation into high-nuclearity metal-cyanide clusters and one-dimensional chain compounds.
The use of multidentate capping ligands has led to the synthesis of a range of new cyano-bridged
cluster geometries, wherein variation of the transition metal ions permits adjustment of the
ground state spin and magnetic anisotropy. In particular, the incorporation of transition metal
ions with a large unquenched orbital angular momentum is found to enhance magnetic relaxation
barriers. Recent work involving the observation of slow magnetic relaxation in mononuclear iron
and uranium complexes will also be presented,1,2 as will attempts to generate well-isolated highspin ground states via electron delocalization in imidazolate-bridged clusters.
Figure. (Color online) Variable-frequency out-of-phase ac susceptibility data for K[(tpaMes)Fe],
collected under a 1500 Oe dc field in the temperature range 1.7 (dark yellow) to 6.0 (magenta)
K.
[1] Rinehart, J. D.; Long, J. R. J. Am. Chem. Soc. 2009, 131, 12558.
[2] Freedman, D. E.; Harman, W. H.; Harris, T. D.; Long, G. J.; Chang, C. J.; Long, J. R. J. Am. Chem. Soc.
2010, 132, 1224.
2- and 3-D M[TCNE]x-based (M = Mn, Fe; TCNE = tetracyanoethylene) Magnets
Joel S. Miller
Department of Chemistry, University of Utah, Salt Lake City, UT 84112-0850
Email:jsmiller@chem.utah.edu
M(TCNE)[C4(CN)8]1/2•zCH2Cl2
(TCNE
=
tetracyanoethylene;
M
=
Mn,
Fe),
[Fe(TCNE)(NCMe)2][FeCl4], and Mn(TCNE)3/2I3/2•zTHF magnets have been have been structurally and
magnetically characterized. Each of these structures has corrugated 2-D layers of S = 1/2 µ4-[TCNE]•bound to and antiferromagnetic coupled to four MII sites. The first compound has these layers are
interconnected with S = 0 µ4-[C4(CN)8]2- providing weak antiferromagnetic coupling and an
antiferromagnetic ground state. [Fe(TCNE)(NCMe)2][FeCl4] does not have interlayer coupling, due to its
terminal MeCN ligands, and is a 2-D ferrimagnet. The layers in Mn(TCNE)3/2I3/2 are connected by S = 1/2
µ4-[TCNE]•- that provides strong, direct antiferromagnetic coupling leading a ferrimagnet with the
highest Tc for this group of organic-based magnets. The structures and magnetic properties of these
materials will be reported.
Kondo Effect in Single-Molecule Magnet Based Transistors
E. R. Mucciolo1,* G. Gonzalez2, M. N. Leuenberger1,3
1
Department of Physics, University of Central Florida, USA
2
3
ITESO University, Mexico
NanoScience Technology Center, University of Central Florida, USA
Email: mucciolo@physics.ucf.edu
We report theoretical investigations of electronic transport in single-electron transistors formed
by an individual single-molecule magnet (SMMs). We show that there is a strong interplay
between the Kondo effect and the quantum tunneling of the magnetization in SMMs. By
applying relatively weak transverse magnetic fields, it is possible to periodically modulate and
even cancel the Kondo effect [1,2]. We provide a microscopic description of this phenomenon as
well as estimates of the Kondo temperature for a certain class of SMMs.
[1] G. Gonzalez, M. N. Leuenberger, and E. R. Mucciolo, Phys. Rev. B 78, 054445 (2008).
[2] M. N. Leuenberger and E. R. Mucciolo, Phys. Rev. Lett. 97, 126601 (2006).
Magnetoelastic Interactions in Molecule-based Materials
J.L. Musfeldt
Department of Chemistry, University of Tennessee
Email: musfeldt@utk.edu
The interplay between magnetism and structure is of great current interest as it may hold clues to
understanding functionality in complex materials. We are now discovering that even “simple” magnetic
ordering transitions may take place with important magnetoelastic effects. More complicated types of
magnetic transitions can be driven by an applied magnetic field, and it is of interest to evaluate the
microscopic aspects of spin-lattice interactions in these cases. In this talk, I will illustrate the use of
magneto-infrared spectroscopy to probe local lattice distortions through the field-driven transition to
the fully polarized state in the quasi-one-dimensional quantum Heisenberg antiferromagnet
Cu(pyz)(NO3)2. Our measurements reveal that 15 T magnetic quantum critical transition takes place with
concomitant changes in the out-of-plane N and C-H bending modes of pyrazine with field that directly
track the magnetization. I’ll discuss our findings in terms of calculated spin densities, scaling laws, and
extracted spin-phonon coupling constants, the latter of which are large due to the softness of the
superexchange ligand.
(Color online)
New Structural Types in Manganese Cluster Chemistry from the Use of AlkoxideBased Ligands
C. Papatriantafyllopoulou,* K. A. Abboud, and G. Christou
Department of Chemistry, University of Florida, Gainesville FL 32611-7200, USA
Email: cpapat@chem.ufl.edu
High-nuclearity manganese cluster chemistry has been attracting intense interest during the last several
years. This is due to the combination of the aesthetically pleasing structures that many such molecular
clusters possess and their often intriguing properties, such as single molecule magnetism (SMM)
behavior. Consequently, the synthesis and characterization of molecules with novel structural types are
of continuing importance in order not only to discover new SMMs but also for a fundamental
understanding of these species. For these reasons, we continue to investigate alternative routes for the
synthesis of new molecules, and one approach that has proven successful is the employment of
pyridine-based alkoxide ligands that upon deprotonation can foster formation of high nuclearity
products. Herein, we describe the syntheses, crystal structures and magnetic properties of mixed-valent
Mn clusters with unprecedented metal topologies containing the anions of (2-hydroxymethyl)pyridine
(hmpH) and (2-hydroxyethyl)pyridine (hepH) as chelating/bridging ligands.
Explorations in Nanoscale Magnetism
Sokrates T. Pantelides,*
Weidong Luo, Sergey N. Rashkeev, Jaume Gazquez, Maria Varela, and Stephen J. Pennycook
Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge TN 37831
Email: pantelides@vanderbilt.edu
The talk will describe recent theoretical work on nanoscale magnetism in several different systems. The
work was motivated by or pursued in the context of scanning transmission electron microscopy and
electron-energy-loss spectroscopy (EELS). Topics include the prediction of s-electron ferromagnetism in
gold nanoclusters and comparison with corresponding results in Pt nanoclusters; the determination of
the origin of room-temperature ferromagnetism in Co-doped TiO2 by combining theory, Z-contrast
imaging and EELS; the resolution of conflicting interpretations of magnetic data at YBCO-LCMO
interfaces by the demonstration of the existence of a magnetic “dead layer” on the LCMO side of the
interface; and the atomic-resolution imaging of nanometer-sized ordered Co spin states in cobaltite
films and corresponding theory.
Phase Solitons in the Spin Ground State of Overdoped Manganites.
Direct NMR Evidence
G. Papavassiliou,1* D. Koumoulis1, N. Panopoulos1, A. Reyes2, M. Fardis1,
M. Pissas1, and D. Argyriou3
1
Institute of Materials Science, NCSR, Demokritos, 153 10 Aghia Paraskevi, Athens, Greece
2
3
National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
Institute Helmholtz-Zentrum Berlin fuer Materialien und Energie (HZB),Glienicker Strasse 100, D-14109,
Berlin,Germany
Email: gpapav@ims.demokritos.gr
The role of stripes in the electronic and magnetotransport properties of hole-doped transition metal
oxide (TMO) compounds, such as high Tc cuprates, nickelates and manganites, is a central issue in the
physics of strongly correlated electron systems.
An important controversy in the physics of these systems is whether the charge ordered ground state in
overdoped manganites, an important sub-class of TMO materials, is a regular arrangement of charge
stripes, or (according to latest experiments) a uniform incommensurate charge and spin density wave. A
clarification of this fundamental question and the examination of its relevance with the stripe phase in
high Tc cuprates and nickelates might have important consequences on our basic understanding of the
stripe phase in hole-doped TMO materials. At the same time, recent theoretical works predicted that
the ground state in overdoped manganites is modulated by an incommensurate (IC) orbital and charge
soliton lattice. However, no experimental evidence for this important prediction has been reported so
far. In this lecture, we shall present latest Nuclear Magnetic Resonance (NMR) results [1], which provide
direct evidence that the spin ground state in La based overdoped manganites is IC modulated with
phase solitons. At higher temperatures the solitonic superstructure is replaced by a uniform spin density
wave, subjected to coherent slow fuctuations, which show a striking similarity with slow fluctuations in
the striped phase of high Tc cuprates and nickelates.
[1] D. Koumoulis, et al., Physical Review Letters 2010, 104, 077204.
Metal Cluster Chemistry of Di-2-pyridyl Ketone and Related Ligands: From HighSpin Molecules and Single-Molecule Magnets to an Exciting New Reactivity
Chemistry of Coordinated Ligands
Spyros P. Perlepes,* Constantinos G. Efthymiou, Alexandros Kitos, Theocharis C. Stamatatos,
Constantinos C. Stoumpos
Department of Chemistry, University of Patras, GR-26504, Patras, Greece
Email:perlepes@patreas.upatras.gr
We shall give in our talk an overview of the coordination chemistry of di-2-pyridyl ketone and related
ligands [1, 2]. Emphasis will be focused on the metal cluster chemistry based on such ligands. The
activation of the carbonyl group(s) of some of the ligands towards further reactions seems to be an
emergent area of synthetic inorganic chemistry. We shall describe the structural features and physical
properties (mainly magnetic) of the resulting polynuclear metal complexes. The structural diversity of
the complexes stems from the ability of the deprotonated diol- or hemiketal-type ligands to adopt a
variety of bridging coordination modes depending on the number of carbonyl groups, the nature of the
extra donor groups in the molecule and on the reaction conditions. Employment of a second organic or
inorganic ligand in this chemistry gives an extraordinary structural flexibility in the resulting metal-ligand
systems. This area of research has something for everyone: from organic and inorganic synthetic
chemistry to metal complexes with impressive structures, and from high-spin molecules to singlemolecule magnets.
[1] A. J. Tasiopoulos, S. P. Perlepes, Dalton Trans., 2008, 5537 (Dalton Perspective).
[2] Th. C. Stamatatos, C. G. Efthymiou, C. C. Stoumpos, S. P. Perlepes, Eur. J. Inorg. Chem., 2009, 3361
(Microreview).
Octanuclear Mixed-Valent Pyrazolato Complexes Containing Fe4O4 Cubanes
Raphael G. Raptis,* Indranil Chakraborty, Kennett Rivero
Department of Chemistry, University of Puerto Rico, San Juan, PR00936-8377, USA.
Email: Raphael@epscor.upr.edu
A family of octanuclear complexes, [Fe8(µ4-O)4(µ-4-R-pz)12X4] (pz = pyrazolate anion; R = H,
Cl, Br, Me, Et; X = Cl, Br, NCS, Oar), containing a Fe4O4-cubane core have been structurally
and spectroscopically characterized.[1] Consecutive reduction steps starting from the all-ferric
complexes, [Fe8], lead to four mixed-valence ferric/ferrous states, [Fe8]–/2–/3–/4–, where the extra
electrons can be localized, partially delocalized, or fully delocalized over the eight Fe atoms of
two distinct sites. Spectroscopic analysis of the mixed-valent [Fe8]– species with X = Cl indicates
partial charge delocalization over the four Fe4O4-cubane Fe-sites with a dominant doubleexchange parameter HAB = 1540 cm–1.[2] Magnetic susceptibility and EPR spectroscopic
measurements show a S = 1/2 ground state. In contrast, the [Fe8]–/2– species with X = NCS
contain FeII-centers fully localized at the outer Fe-sites. Current efforts to fully characterize,
structurally, spectroscopically and magnetically the Fe8O4-motif in all its possible oxidation
states will be presented. We will also report on recent progress on the synthesis and
characterization of [In4Fe4(µ4-O)4(µ-4-R-pz)12X4] complexes, structurally analogous to the alliron [Fe8] variety, but containing the magnetically simpler In4Fe4(4-O)4 core.
Figure. (Color Online) Ball-and-stick diagram of Fe8(µ4-O)4(µ-pz)12Cl4.
[1] R. G. Raptis et al., Inorg. Chem. 2008, 47, 645.
[2] R. G. Raptis et al., Inorg. Chem. 2008, 47, 11734.
Spin Relaxation in Some Transition Metal Clusters
Y. Sanakis
Institute of Materials Science, NCSR “Demokritos”, 15310 Ag. Paraskevi, Attiki, Greece
Email: sanakis@ims.demokritos.gr
The trinuclear complex [Bu4N]2[Cu3(µ3-Cl)2(µ-pz)3Cl3] (pz = pyrazolato anion) (1) exhibits ferromagnetic
interactions resulting in an S = 3/2 ground state which is characterized by a small zero field splitting
tensor. Electron Paramagnetic Resonance spectroscopy at low and high frequencies and magnetic fields
is applied to characterize the zero field splitting tensor of the S = 3/2 state. The spin relaxation
properties of 1 are studied with alternating current susceptometry in the presence of external magnetic
fields. In the 4.5 – 8.0 K temperature range, the system relaxes via an Orbach mechanism involving
transitions between the S = 3/2 and the excited S = 1/2 spin manifolds.
Figure. (Color online) Alternating Current magnetic susceptibility studies of 1 in the presence of 1.0 kOe.
The relaxation properties of 1 are compared with those of other Cu(II)- or Fe(III)- based polynuclear
transition metal clusters.
[1] R. Boča, L. Dlhan, G. Mezei, T. Ortiz-Perez, R. G. Raptis, J. Telser, Inorg. Chem., 2003, 42, 5801.
Magnetically Bistable Complexes
Incorporating Redox-Active Organic Moieties
M. Shatruk,* L. Ray, J. Hoyt
Department of Chemistry & Biochemistry, Florida State University, Tallahassee, FL 32306, USA
Email: shatruk@chem.fsu.edu
The recent interest in combining tetrathiafulvalene (TTF), a ubiquitous component of synthetic organic
conductors, with various transition and rare-earth metal ions is expected to result in novel
multifunctional materials with appealing optical, electronic, and magnetic characteristics. With the goal
to combine conductivity with magnetic bistability in a single molecule-based material, we focused on
incorporating TTF moieties into metal complexes that exhibit spin crossover and single-molecule
magnetism. Using TTF-fused 1,10-phenanthroline (edt-TTF-phen) reported by us earlier,1 we prepared a
mononuclear complex [Fe(edt-TTF-phen)2(NCS)2] that undergoes temperature-induced transition from
the high-spin to low-spin state at the Fe(II) center. The high-spin state can be frozen by rapid cooling to
30 K and relaxes back to the low-spin state and then again to the high-spin state upon increasing
temperature. The use of TTF-functionalized phthalocyanines Pc(TTF)4 has allowed the preparation of
double-decker complexes of Tb, Dy, and Ho. The former exhibits single-molecule magnetic behavior,
similar to that observed for the “TTF-free” TbPc2 complex.2 Furthermore, the use of scanning tunneling
microscopy allowed visualization of Tb[Pc(TTF)4]2 at single-molecule level.
[1] Keniley, L. K.; Ray, L.; Kovnir, K.; Dellinger, L. A.; Hoyt, J. M.; Shatruk, M. Inorg. Chem. 2010, 49, 1307
[2] Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.-Y.; Kaizu, Y. J. Am. Chem. Soc. 2003, 125, 8694.
Photoresponsive Cobalt-bis(Dioxolene) Valence Tautomers: Molecular
Properties and Progress toward Devices
David A. Shultz* and Robert D. Schmidt
Department of Chemistry, NC State University, Raleigh, NC 27695-8204
Email: Shultz@ncsu.edu
Preparation and characterization of cobalt bis(dioxolene) valence tautomers will be discussed along with
strategies for incorporating them into molecular devices.
Mesoscopic Physics in Antiferromagnetic Chromium Films
Yeong-Ah Soh
Department of Materials, Imperial College, London, UK
Email: ya.soh@imperial.ac.uk
We recently discovered electrical effects due to quantization of spin-density waves (SDW) in Cr films [1].
Measurement of the strain wave/charge-density wave (SW/CDW) on two of our thin Cr films using hard
x-rays shows quantization of the strain wave that is in excellent agreement with the transport data. The
wavelength of the strain wave is quantized such that half-integer number of periods are accommodated
within the film thickness. The quantization value changes as a function of temperature, and in some
temperature windows, there is coexistence of two quantized values. Using x-ray microdiffraction we
spatially mapped the distribution of domains corresponding to the two quantized strain waves. In
addition, as a result of the phase locking of the quantized strain wave the x-ray measurements show
new interference effects not observed in bulk samples.
[1] "Electrical effects of spin density wave quantization and magnetic domain walls in chromium", Ravi
K. Kummamuru and Yeong-Ah Soh, Nature 452, 859 - 863 (2008).
Structural Aesthetics in Molecular 3d-Metal Cluster Chemistry: New HighNuclearity Manganese Single-Molecule Magnets Bearing the Anions of
Triethanolamine
Theocharis C. Stamatatos,* a,b Dolos Foguet-Albiol,a Wolfgang Wernsdorfer,c Khalil A. Abboud,a George
Christoua
a
b
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA
Present address: Department of Chemistry, University of Patras, Patras 26500, Greece
c
Institut Néel, CNRS & Université J. Fourier, BP-166, Grenoble, Cedex 9, France
Email: thstama@chemistry.upatras.gr
One of the current challenges in inorganic chemistry is the synthesis and characterization of new
molecular 3d metal polynuclear clusters at moderate oxidation states. Reasons for this are varied, and
not least among them is the aesthetic beauty that develops as the nuclearity of the clusters increases
and the complexity of their molecular structures becomes apparent. From a more practical viewpoint,
such large clusters can represent an alternative, ‘bottom-up’ route to nanoscale particles
complementary to the traditional ‘top-down’ approach. An example is the discovery that molecular 3dmetal clusters can function as magnets, providing a ‘bottom-up’ approach to nanoscale magnetic
materials, and such individual molecular species have come to be known as single-molecule magnets
(SMMs). In the present talk, we discuss our results from the combined use of azides, carboxylates, and
the potentially tetradentate (N,O,O,O) triethanolamine (teaH3) chelating/bridging group in mixedvalence Mn cluster chemistry [1].
[1] Th. C. Stamatatos, D. Foguet-Albiol, W. Wernsdorfer, K. A. Abboud, G. Christou, Chem. Commun.,
submitted.
Almost absolute modulation of the transport properties of a superconductor
by means of ferromagnetic ingredients: Co/Nb/Co nanostructured trilayers
D. Stamopoulos,1,* E. Manios1, E. Aristomenopoulou1, M. Sandim2, G. Papavassiliou1, M. Pissas1
1
2
Institute of Materials Science, NCSR ‘Demokritos’, Aghia Paraskevi, 153-10, Athens, Greece
Escola de Engenharia de Lorena, Universidade de São Paulo, Lorena 12600-970, SP, Brazil
* Email: densta@ims.demokritos.gr
Recent theoretical models propose that in FM/SC/FM trilayers (TLs) (right panel in Figure
below) the transport properties of the SC interlayer can be controlled by the in-plane relative
magnetization configuration of the outer FM layers; the antiparallel (parallel) in-plane
magnetic configuration enhances (suppresses) SC (spin-valve effect). Another effect that relates
to the change of the transport properties of the SC interlayer under the influence of the out-ofplane magnetization components is the so-called magnetoresistance effect (MRE). Our former
experiments on MRE [1] were conducted on NiFe/Nb/NiFe TLs and showed that the MRE peaks
correlate nicely with the peaks in the out-of-plane component of the outer FMs magnetization.
This illustrates that the transverse magnetostatic coupling of the outer FM layers through stray
fields that pierce the SC interlayer is the underlying mechanism motivating the MRE.[1]
Here we focus on the MRE in Co/Nb/Co TLs by investigating a wide range of Co and Nb
thickness, 10-60 nm and 15-100 nm, respectively. It is well known that at a critical thickness, dcr
of 30 nm Co films change magnetization orientation by exhibiting in-plane for d<30 nm to outof-plane for d>30 nm. Taking this fact into account we investigated TLs in which the Co outer
layers have thickness well below and well above dcr since we expected that MRE should be
minor (major) in the first (second) class. TLs with Co thickness equal to d=60nm>dcr obtain an
almost absolute MRE, with values over 80% at a temperature range of 19 mK around Tc (left
panel in Figure below), while for Co thickness d=10nm<dcr MRE is minimum.[2] Furthermore,
a high (low) MRE is observed when the Co layers have the same (different) coercive fields,
confirming that the transverse magnetostatic coupling of the two FM layers enhances MRE.[2]
0.20
7.43
R (Ohm)
0.15
0.10
FM
SC
FM
7.42
0.05
T=7.4 K
0.00
-10 -8 -6 -4 -2 0
Virgin
2
H (kOe)
4
6
8 10
Figure. (Right) Schematic illustration of a FM/SC/FM TL and (Left) raw R(H) data around T c that
demonstrate the almost absolute MRE observed in the Co/Nb/Co TLs studied here.
[1] D. Stamopoulos, E. Manios, and M. Pissas, Phys. Rev. B, 75, 2007, 184504
[2] D. Stamopoulos, E. Manios, E. Aristomenopoulou, M.J.R. Sandim, G. Papavassiliou, M.
Pissas, submitted for publication
Random-field Ising Ferromagnetism in Mn12-acetate: the Role of
Ligand Disorder
P. Subedi,1* A.D. Kent,1* Bo Wen,2 Lin Bo,2 Y. Yeshurun,1,2,3 M.P. Sarachik, 2
A.J. Millis,4 C. Lampropoulos5 and G. Christou5
1
Department of Physics, New York University, 4 Washington Pl, New York, NY 10003, USA
2
Department of Physics, City College of New York, CUNY, New York, New York 10031, USA
3
Dept. of Physics, Institute of Nanotechnology, Bar-Ilan University Ramat-Gan 52900, Israel
4
Department of Physics, Columbia University, New York, NY 10027, USA
5
Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA
Email: pradeep.subedi@nyu.edu, andy.kent@nyu.edu
The temperature dependence of the inverse magnetic susceptibility of Mn12-acetate is found to
give finite temperature intercepts corresponding to a Curie-Weiss temperature TCW, indicating a
transition to a ferromagnetic phase at low temperature due to dipolar interactions. With increasing
magnetic field applied transverse to the easy axis, the temperature dependence of the susceptibility
exhibits significant departures from Curie-Weiss behavior and (inferred) Curie-Weiss intercepts that
decrease with transverse field considerably more rapidly than predicted by mean field theory for a
perfectly ordered Mn12-acetate single crystal.
We suggest that our experimental results can be
explained in terms of random field Ising ferromagnetism (RFIFM) in a transverse field, where the
randomness is due to the ligand disorder which is known to cause a distribution of molecular easy axis
tilts in Mn12-acetate. From theoretical calculations we infer the effect of the random field on the
susceptibility, including its dependence on the magnitude and orientation of the applied transverse
field. In particular, we show how measurement of the field dependence of the magnetic susceptibility
can be used to reveal the mean square random magnetic field as well as the distribution of the random
fields.
New High Spin and High Nuclearity Manganese Clusters from the Introduction of
Bulky Groups into 2-(hydroxymethyl)pyridine
Taketo Taguchi,* Khalil A. Abboud and George Christou
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200
Email: ttaguchi@chem.ufl.edu
High-nuclearity Mn clusters continue to attract much attention for reasons such as their aesthetically
pleasing structures, the large numbers of unpaired electrons they often possess, and their ability often
to function as single-molecule magnets (SMMs). We are continuing to explore development of new
synthetic routes to Mn clusters. One chelating and bridging ligand that has given many interesting new
clusters in the past has been the anion of 2-(hydroxymethyl)pyridine (hmp-). In the present study,
derivatives of hmp- containing substituents of different bulkiness at the CH2 position have been
employed in order to explore whether this might lead to distinctly different products. This has indeed
been found to be the case: the anions of 2-(diphenylhydroxymethyl)pyridine (dphmp-) and 2(dimethylhydroxymethyl)pyridine (dmhmp-) have yielded new and novel structural types of Mn clusters
with nuclearities of Mn4, Mn6, Mn7, Mn11 and Mn12. In this presentation, the syntheses, structures, and
magnetic properties of these products will be described, as well as a rationalization of the product as a
function of the bulkiness of the chelate employed.
CH3
CH3
N
hmpH
OH
dmhmpH
Photoinduced Magnetization Effects in
dphmpH
Nanometer Scale Heterostructures of Prussian Blue Analogs
Daniel R. Talham,1,* Matthieu F. Dumont,1 Matthew J. Andrus,1 Daniel M. Pajerowski,2 Elisabeth S.
Knowles,2 and Mark W. Meisel2
1
Department of Chemistry, University of Florida, Gainesville, FL, 32611-7200, United States.
2
Department of Physics and National High Magnetic Field Laboratory, University of Florida, Gainesville,
FL, 32611-8440, United States.
Email: talham@chem.ufl.edu
Nanometer scale heterostructures of Prussian blue analogs lead to new phenomena not observed for
the constituent bulk phases. A striking example1 is the ABA heterostructured thin film comprised of
ferromagnetic Rb0.8Ni4.0[Cr(CN)6]2.9.nH2O (Ni-Cr PBA) and the photomagnetic Rb0.7Co4.0[Fe(CN)6]3.nH2O
(Co-Fe PBA). The films experience a significant increase in the temperature, from 18 K to 75 K, at which
large persistent photoinduced changes in magnetization occur. The behavior results from a new
mechanism for inducing magnetization changes in molecule-based magnetic materials using light. Light
induced structural changes in the Co-Fe PBA layer couple to the adjacent network, leading to changes in
magnetization in the higher ordering temperature Ni-Cr PBA analog, and the behavior results from the
ability to couple the two materials at the nanometer length scale. In general, achieving nanoscale
heterostructures of molecule-based networks and solids requires new synthetic approaches and this
system along with other thin film and nanoparticle examples will be discussed.
200nm
Left. Scheme and TEM cross section of an ABA heterostructured thin film of two
Prussian blue analogs.1 The scale bar is 100 nm. Right. TEM image of a BAB
heterostructured particle of the same materials.
1. D. M. Pajerowski et al. J. Am. Chem. Soc. 2010, 132, 4058-59.
New High Nuclearity, High Spin Metal Clusters and SMMs from the Use of
Aliphatic Diols in Manganese-Carboxylate Chemistry
Anastasios J. Tasiopoulos,a, * Eleni E. Moushi,a Maria Charalambous, a Christos Lampropoulosb,
Theocharis C. Stamatatosb, Vassilios Nastopoulosc, Wolfgang Wernsdorferd, George Christoub
a
b
Department of Chemistry, University of Cyprus, 1678 Nicosia, Cyprus
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200,USA
c
Department of Chemistry, University of Patras, 26504 Patras, Greece
d
Institut Néel-CNRS, 38042 Grenoble, Cedex 9, France
e-mail: atasio@ucy.ac.cy
The current intense interest in Manganese-carboxylate chemistry has resulted to a number of beautiful
complexes, some of which contain a large number of metal ions (up to 84). The main reason for this
interest is the fact that such molecules can function as magnets below a critical temperature, providing
a new ‘bottom-up’ approach to nanoscale magnetic materials. [1] Our group, has been exploring over
the last few years the use of 1,3-propanediol (H2pd) and 2-methyl-1,3-propanediol (H2mpd) in Mn
carboxylate chemistry as a route to new polynuclear clusters and SMMs. [2]
We will report, the synthesis, crystal structures and magnetic properties of a series of new polynuclear
clusters that were prepared from the use of H2pd and H2mpd in Mn – carboxylate chemistry. The list of
the new compounds that shall be described include high spin Mn17 octahedra, Mn15 loops incorporating
supertetrahedra and Mn40Na4 and Mn44 loops of loops.
Figure. (Color Online) A Mn15 cluster that consists of a loop that is incorporating a supertetrahedron
Acknowledgements: The authors would like to thank the Cyprus Research Promotion Foundation (Grant:
ΔΙΕΘΝΗΣ/ΣΤΟΧΟΣ/0308/14) for the financial support.
References
[1] R. Sessoli, H.-L. Tsai, A. R. Schake, S. Wang, J. B. Vincent, K. Folting, D. Gatteschi, G. Christou, D. N.
Hendrickson, J. Am. Chem. Soc. 1993, 115, 1804.
[2] a) E. E. Moushi, T. C. Stamatatos, W. Wernsdorfer, V. Nastopoulos, G. Christou, A. J. Tasiopoulos, Angew.
Chem. Int. Ed. 2006, 45, 7722; b) E. E. Moushi, C. Lampropoulos, W. Wernsdorfer, V. Nastopoulos, G. Christou,
A. J. Tasiopoulos, Inorg. Chem. 2007, 46, 3795; c) E. E. Moushi, T. C. Stamatatos, W. Wernsdorfer, V.
Nastopoulos, G. Christou, A. J. Tasiopoulos, Inorg. Chem. 2009, 48, 5049.
Nanoscale Magnets: Free Rotors and Quantum Mechanical Rotation
J. Tejada
Facultat de Física, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
Email: jtejada@ubxlab.com
In my talk I will review different experimental results suggesting the existence of personel that magnetic
nanoscale free rotors. The nanoparticles are made of Fe2O3 which are dispersed in methanol-based
ferrofluid and CoFe2O4 inside a porous polymeric matrix. The data presented are magnetic and
microwave absorption. The mechanical rotation of these nanoscale magnetic compasses is quantized
being, therefore, the largest objects showing such quantum behaviour. It is important to remark that the
data of our resonant absorption experiments have been interpreted by considering the rotational
Doppler used to shift the frequency of the resonant absorption.
J. Tejada et al. Phys. Rev. Lett.,104, 027202 (2010)
Structure and Magnetism of Diverse Polynuclear (Ni4, Ni16 , Mn12, Cu11)
Assemblies with Tetratopic Pyridazine and Pyrimidine Ligands
L.K. Thompson,* K.V. Shuvaev, S.S. Tandon and L.N. Dawe
Dept. of Chemistry Memorial University, St. John’s Newfoundland, A1B 3X7 Canada
Email:lk.thompson@mun.ca
Successful self-assembly of 2-D [nxn] polymetallic grids requires a good match between the
ligand and the ‘coordination algorithm’ of the metal ion. Ligands like L1 produce M 16
magnetically coupled square [4x4] grids (M = Mn(II),Cu(II)) with ease. 1 Kinetic and
thermodynamic factors are important in the self-assembly process, but metal ion crystal field
stabilization energy (CFSE) also plays a significant role. With the isomeric ligands L1, L2
Ni(II) prefers to form linear spiral chains, dominated by N 6 donor coordination (increased
CFSE), e.g. [Ni4(L2)3](ClO4)2.2 However with L4 a Ni(II) 16 grid forms, comprising four
connected smaller [2x2] square grids, similar to μ-O bridged Ni(II)4 grids with analogous
ditopic ligands.1 Changing the ligand ends to bipy in L3 creates a strong ligand based
perturbation, upsetting the balance of grid based instructions, resulting in the formation of a
novel Cu(II)11 super-triangle, and a Mn(II) 12 incomplete square based grid. Magnetic
properties, dominated by antiferromagnetic exchange, will be discussed using simplified
exchange models for the large clusters, based on molecular pseudo-symmetry and orbital
orthogonality considerations.
R'
N N
Ni1
R'
N N
N N
R''
R''
Ni5
Ni13
Ni9
Ni2
Ni6
Ni10
Ni3
Ni7
Ni8
Ni11
Ni14
R
R
L1(R=NH2,R'=OH,R''=py), L2(R=OH,R'=NH2,R''=py)
L3(R=OH,R'=NH2,R''=bipy)
N
M
N
N
OH M
NH2
NH2
N
N
N
L4
M
N
Ni15
N
OH M
Ni4
Ni12
Ni16
Figure. (Color online) Tetratopic ligands and Ni16 grid
[1] L.N. Dawe, K.V. Shuvaev, L.K. Thompson, Chem. Soc. Rev., 2009, 38, 2334.
[2] K.V. Shuvaev, T.S.M. Abedin, C.A. McClary, L.N. Dawe, J.L. Collins, L.K. Thompson, Dalton Trans, 2009,
2926.
The Nanoscopic Spin Frustrated Cluster V15: a Unique Polyoxometalate
Boris Tsukerblat
Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel
Email: tsuker@bgu.ac.il
In context of the interest to single molecule magnetism and quantum computing much attention last
decade has been attracted to an unique layered mesoscopic vanadium polyoxometalate
K6[VIV15As6O42(H2O)]·8H2O (V15) containing 15 VIV ions [1]. Here we present an overview of the magnetic
interactions in this fascinating system with the emphasis on a special role of the
O
AsIII
VIV
Figure. (Color Online) Ball-and-stick representations of the cluster anion [VIV15As6O42(H2O)]6–
antisymmetric (AS) exchange in spin frustrated systems. The following questions will be discussed: 1)
spin states, three spin model, “accidental” degeneracy vs orbital degeneracy, concept of spin
frustration; 2) AS exchange and magnetic anisotropy; 3) rules for crossing/anticrossing of the Zeeman
levels, crucial role of symmetry, staircase field dependence of magnetization; 3) pseudo-angular
momentum, selection rules in EPR, structural factors, experimental data; 4) spin frustration and spinvibronic Jahn-Teller effect, structural instability vs magnetic anisotropy;
5) Rabi oscillations in a
molecular magnet V15, coherence [2].
[1] P. Kögerler, B. Tsukerblat, A. Müller, Dalton Transactions, 2010, 39, 21
[2] S. Bertaina, S. Gambarelli, T.Mitra, B. Tsukerblat, A. Müller, B. Barbara, Nature, 2008,
453, 203
Covalently-Bridged Spin Ladders: Variable Exchange Through Diazine Ligands
M.M. Turnbull,1* R.T. Butcher,1 C.P. Landee,2 J. Jornet,3 M. Deumal,3 J.J. Novoa3
1
Carlson School of Chemistry and 2Dept. of Physics, Clark University, Worcester, MA 01610 3Departament
de Química Física, Universitat de Barcelona, Diagonal 647, Barcelona, Spain Email:
mturnbull@clarku.edu
Our interests in low-dimensional magnetic lattices has led us to study a
family of complexes, Cu(diazine)X2, where X = Cl, Br and the diazine is a
substituted pyrazine, quinoxaline, or a substituted quinoxaline. The
complexes crystallize in the monoclinic space group C2/m as covalently
bridged ladders where the rungs are formed by halide bridges and the rails
are formed by the bridging diazine.[1] Magnetic susceptibility data on
these complexes reveals an interesting anomaly. When the diazines are
2,3-dimethypyrazine (2,3-dmpz) or quinoxaline, there is a significant
change in the magnetic exchange constants (2J/kB), when the halide ion is
switched from chloride to bromide (see Table). Surprisingly, the major
change is not the rung exchange (via the halide ion), but rather exchange
along the rails (through the diazine) which changes dramatically. The
syntheses, structures, magnetic data and theoretical verification of the
observed exchange will be presented.
Structure of Cu(2,3-dmpz)Br2
Table. Fitted magnetic exchange values (K) for four Cu(diazine)X2 compounds
Cu(quinox)Br2
Cu(quinox)Cl2
Cu(2,3-dmpz)Br2
Cu(2,3-dmpz)Cl2
2J/kB (rung)
- 35
- 34.5
- 28.3
- 28.4
2J/kB (rail)
- 30.3
- 19.1
- 21.4
- 14.5
[1] R.T. Butcher, L.N. Dawe, C.P. Landee and M.M. Turnbull, Polyhedron, 2009, 28, 1710.
Insight into the Mechanism of O2 Activation and Oxygen Atom Transfer (OAT) by
an OCO3- Trianionic Pincer CrIII Complex: Significance of a Three Coordinate
Ligand
A.S. Veige
Center for Catalysis, University of Florida, P.O. Box 117200, Gainesville, Florida, 32611
Email: veige@chem.ufl.edu
A kinetic and mechanistic investigation of a chromium(III) aerobic oxidation catalyst supported by an
OCO3- trianionic pincer ligand provides insight into a key ligand design feature.
The complex
t
t
III
t
[ BuOCO]Cr (THF)3 (1) (where BuOCO = 2,6-C6H3(6- BuC6H3O)2) catalyzes oxidation of
triphenylphosphine (PPh3) with 1 atm of O2 with a TON = 200 (turnover number = moles of substrate
converted/moles of catalyst). The oxidation of 1 with O2 (1 atm) yields an isolable CrVO complex
[tBuOCO]CrV(O)(THF) (2). Complex 2 is a d1 paramagnetic complex and was characterized by 1Kinetic
analysis of the O2 activation by 1 reveals first-order kinetics in both 1 and O2, and inverse first-order in
THF. Once the CrVO complex forms, it swiftly transfers the oxygen atom to PPh3. Stoichiometric
oxygen-atom-transfer (OAT) reactions from 2 to PPh3 is 1st order in 2 but 2nd order in PPh3. This implies
one equivalent of PPh3 must add to the complex to activate or weaken the Cr VO bond before the transfer
can occur. Related to this observation, during catalysis, product (OPPh3) does not inhibit. In fact,
increasing OPPh3 concentration accelerates O2 activation. When 1 is treated with excess OPPh3, the fivecoordinate complex [tBuOCO]CrIII(OPPh3)2 (3) forms and is isolated and characterizaed by cyclic
voltametry, X-ray crsytallography, 31P{1H} NMR, epr, and UV-vis spectroscopy.
Figure 1. Five coordinate [tBuOCO]CrIII(OPPh3)2 (3).
Molecular Nanomagnets:
A Challenge for Quantum Many-body Physics in Mesoscopic Spin Systems
Oliver Waldmann
Physikalisches Institut, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany
Email: oliver.waldmann@physik.uni-freiburg.de
Molecular nanomagnets establish a new class of magnetic materials providing a fascinating view on the
magnetism of small, nanosized objects. These molecules typically consist of tens of magnetic metal ions,
which are linked by organic ligands such as to form well defined geometrical structures. The magnetic
exchange couplings between the metal ions within a molecule frequently are antiferromagnetic in
nature, which gives rises to a competition between the quantum correlations injected by the
antiferromagnetic paths and the constraints due to the topology of the lattice of metal ions. Spin
frustration is a prominent example of that, but other complex many-body wave functions can emerge,
yielding unprecedented magnetic behavior.
In this talk, molecular nanomagnets will be regarded from the perspective of many-body physics in
"small" quantum systems. Here, small means that the number of magnetic centers in the molecule is
large enough for non-trival magnetic behavior to appear but also small enough not to approach the
thermodynamic limit. In recent years, the size of the clusters under study has tended to increase, which
has made it more and more difficult to understand the structure of the emerging many-body wave
functions and their associate quantum magnetism. Several examples of our work will be discussed,
which shall demonstrate the challenges in understanding elementary spin excitations in small quantum
spin systems.
Longitudinal Susceptibility Measurement of Mn12-ac Single Crystals as a
Function of Temperature and Transverse Magnetic Field
Bo Wen,1 * M. Sarachik,1 * P. Subedi,2 S. Li,1 L. Bo,1 Y. Yeshurun,1,2,3
A. D. Kent,2 A. Millis,4 C. Lampropoulos,5 and G. Christou5
1
Department of Physics, City College of New York, CUNY, New York, New York 10031, USA
2
Department of Physics, New York University, New York, New York 10003, USA
3
Dept. of Physics, Institute of Nanotechnology, Bar-Ilan University, Ramat-Gan 52900, Israel
4
Department of Physics, Columbia University, New York, New York 10027, USA
5
Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA
Email: wenboown@sci.ccny.cuny.edu, sarachik@sci.ccny.cuny.edu
The temperature dependence of the longitudinal magnetic susceptibility has been investigated
in magnetic fields up to 5 T applied transverse to the easy axis of single crystals of Mn 12-ac. In the
absence of transverse field, local measurements obtained by micro-Hall magnetometry and global
measurements of the whole sample in a SQUID-based Quantum Design MPMS magnetometer both yield
Curie-Weiss behavior with a finite temperature intercept, indicating a transition to dipolar
ferromagnetism at a Curie temperature Tc ~ 0.8 K. A transverse magnetic field suppresses Tc more
rapidly than expected from mean field calculations for a simple Ising ferromagnet in a transverse field.
To ensure that measurements were obtained for the system in equilibrium, we determined the
blocking temperature as a function of transverse field and of the sweep-rate of the longitudinal field.
Slower sweep rates allow more time for equilibration, while transverse fields accelerate the relaxation
toward equilibrium and lower the blocking temperature, as expected based on the Mn12-ac spinHamiltonian and a classical model of single domain uniaxial nanomagnets.
Molecular Spintronics using Molecular Nanomagnets
Wolfgang Wernsdorfer
Institut Néel, CNRS, BP 166, 38042 Grenoble Cedex 9, France
Email: wolfgang.wernsdorfer@grenoble.cnrs.fr
This presentation will address a new field called molecular spintronics, which combines the concepts of
spintronics, molecular electronics and quantum computing [1]. Various research groups are currently
developing low-temperature scanning tunnelling microscopes to manipulate spins in single molecules,
while others are working on molecular devices (such as molecular spin-transistors, spin valves and
filters, and carbon-nanotube-based devices [1]) to read and manipulate the spin state and perform basic
quantum operations. The talk will discuss this - still largely unexplored - field and present our first results
(Figure) [1].
Figure 1. (Color online) Molecular double-dot devices. Magnetic molecules proposed for grafting on
suspended carbon nanotubes connected to Pd electrodes (form left to right): a C60 fullerene including a
rare-earth atom, the Mn12 SMM and the rare-earth-based double-decker [Tb(phtalocyanine)2] SMM. The
gate voltage of the double-dot device is obtained by a doped Si substrate covered by a SiO2 insulating
layer
[1] L. Bogani & W. Wernsdorfer, Molecular spintronics using single-molecule magnets, Nature Mat. 7,
179 (2008).