Tuesday 9 July 2013, Strathblane & Cromdale Halls, 16:30-18:30
Poster session A - Thin film magnetism, nano magnetism and molecular magnetism
P.169 Quantitative analysis of structural disorder in Ni1.5[Cr(CN)6].zH2O molecular magnet using Reverse Monte
Carlo simulation of neutron diffraction patterns
P Bhatt and S M Yusuf
Solid State Physics Division, Bhabha Atomic Research Centre, India
Prussian blue analogues (PBAs) molecular magnets, represented by a common formula AIIk[BIII(CN)6]l·zH2O (A and B
are 3d transition metal ions) have attracted much attention in recent years due to their multifunctional properties.
The valence modulation, an appropriate choice of transition metal ions, B(CN)6 vacancies, and water content leads
to change in their physical properties [1-3] and develops structural disorder/defects in PBAs. Ni1.5[Cr(CN)6].zH2O
compound is synthesized using co-participation method at room temperature. The neutron diffraction (ND)
measurements are carried out to investigate the structural properties of the compound. The Rietveld refinements of
the ND patterns reveal that, the sample is in single phase with face-centered cubic crystal structure with space
group Fm3m. The dc magnetization study confirms a soft ferromagnetic nature of the compound with Curie
temperature of 50 K. A study of structural disorder is carried out using a Reverse Monte Carlo (RMC) simulation
method on the powder ND patterns recorded at 300 K (paramagnetic phase) and 6 K (ferromagnetic phase). The
RMC study confirms that, the water molecules, due to vacancies of [Cr(CN)6], are mainly responsible for the
structural disorder. Moreover, the partial pair correlation functions between the oxygen atoms of the water
molecules (first nearest neighbour distance 3Å), present in the compound are quantified.
[1]
[2]
[3]
Pramod Bhatt, S. M. Yusuf, M. D. Mukadam, J. V. Yakhmi J App Phys 2010, 108, 023916
Pramod Bhatt, N. Thakur, M. D. Mukadam, S. S. Meena, S. M. Yusuf J Phys Chem. C 2013,
10.1021/jp312395y
Pramod Bhatt, S. M. Yusuf, R. Bhatt, G. Schütz J Solid State Electrochem2013, 10.1007/s10008-0121995-x
P.170 Polarized Neutron Reflectometry of thermally treated Ni/Zr multilayers
D Bhattacharya, S Basu and S Singh
Bhabha Atomic Research Centre, India
Diffusion-limited reactions occurring during annealing of multilayer structures can induce alloying and interlayer
growth across interfaces. Such interfacial layers are often too thin to be measured by conventional diffraction
methods, but can be precisely determined by Polarized Neutron Reflectometry (PNR). This is a highly sensitive, nondestructive technique applied to thin films and multilayers in order to obtain area-averaged chemical composition
and magnetization with depth. Used in specular mode, it provides information on the neutron refractive index profile
normal to an interface. One of the major advantages of PNR is that it can detect small magnetic moments with
excellent depth resolution.
In the present work PNR (at Dhruva reactor, India) was employed to investigate chemical and magnetic changes in
Ni/Zr multilayer structures induced by thermal annealing. Analyses of the reflectivity data indicated that
interdiffusion among the various layers had occurred, leading to interfacial alloy formation. The extent of diffusion
was correlated with annealing time. The study of Ni-Zr alloys is important to understand the formation mechanism of
metallic glasses which have useful properties like corrosion resistance and find applications in nuclear reactor
engineering and bio-medical industries.
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P.171 Polarized Neutron and X-ray Reflectometry: Complementary tools to probe chemical and magnetic properties
of layered structures
D Bhattacharya1, S Basu1, S Roy1 and B N Dev2
1
Bhabha Atomic Research Centre, India, 2IACS, India
Ferromagnetic/non-magnetic semiconductor layered structures are potential candidates for the development of
magnetic random access memory devices. Interfacial mixing across the metal/Si interfaces can occur in these asdeposited samples due to free energy conditions governing the system. This can lead to the formation of ultrathin
interfacial alloys that may or may not be magnetic. In such cases Polarized Neutron Reflectometry (PNR) serves as
an invaluable tool used to determine the magnetization profile at surfaces and interfaces of thin films and
multilayers. The high degree of surface (and interface) sensitivity of this powerful technique to differences in
refractive indices of adjacent layers in a stratified structure essentially enables structural characterization as well.
Utilizing PNR in conjunction with the complementary X-ray reflectivity (XRR) technique generates a depth dependent
chemical and magnetic structure averaged over lateral dimensions of the entire sample. This includes quantitative
estimation of thickness, roughness and density of the constituent and interfacial layers and also provides an
excellent handle to obtain stoichiometry of alloy layers at the interfaces of a binary system.
The present work investigates room temperature diffusion in a trilayer system: Si/Co/Si, using a combination of XRR
and PNR data analyses. Characterization of the system revealed the formation of ultra thin interfacial non magnetic
alloys, whose respective stoichiometries were also assessed. Reflectometry data were also used to calculate and
explain an unusually high magnetic moment for the Co layer.
P.172 Neutron reflectivity of electrodeposited thin magnetic films
J Cooper1, K N Vyas2, N J Steinke1, D M Love2, C J Kinane1 and C H W Barnes2
1
STFC, UK, 2University of Cambridge, UK
Electrodeposition is an inexpensive and energy efficient method of growing high quality magnetic thin film devices.
Liquid phase growth techniques allow conformal (non-line of sight) growth, however introduces new idiosyncrasies
compared with traditional UHV techniques. These are especially important at layer boundaries and to characterise
these we require the ability to probe buried interfaces.
We present a polarised neutron reflectivity study of magnetic/non-magnetic (CoNiCu/Cu) thin films grown by single
bath electrodeposition. We find that the composition is neither homogeneous with time, nor the same as the bulk
values found by energy dispersive x-ray spectroscopy of thicker films. Instead a non-magnetic copper rich layer is
initially formed, around 2 nm thick, before the material becomes magnetic. This is due to the time evolution of the
mass transport limiting of the copper by diffusion. Beyond a single layer this copper region is supressed and as
such may be compensated for by growing a copper buffer layer immediately preceding the growth of the rest of the
device.
In line with many previous studies, cobalt deposits anomalously compared to nickel. The nickel suppression allows
the scattering length and magnetic moments to be fitted independently and compared to prove a self-consistent
model.
ICNS 2013 International Conference on Neutron Scattering
P.173 Towards determination of the directionally resolved magnetization relaxation in iron oxide nanoparticle
mesocrystals
S Disch1, E Wetterskog2, G Salazar-Alvarez2, L Bergström2 and A Wiedenmann1
1
Institut Laue-Langevin, France, 2Stockholm University, Sweden
Self-assembly of nanoparticles is a promising technique for exploration of novel functional materials [1]. Obtained
model systems for investigation of interparticle interactions allow for understanding the collective properties arising
in ordered nanoparticle mesostructures [2]. In particular the shape induced order of anisotropic nanoparticles is
attracting growing interest due to its potential for materials with anisotropic properties [3]. Stroboscopic SANS and
the new TISANE technique can be applied to monitor the time resolved fluctuation of the nanoparticle magnetization
to a periodic perturbation from an oscillating external magnetic field, giving access to the microscopic magnetization
relaxation in nanomaterials [4].
In this contribution, we will present long range ordered assemblies of iron oxide nanocubes and the influence of
interparticle interactions on the magnetization relaxation. The mesostructure of the assemblies is substantially
influenced by very small changes in the particle shape [5,6]. We will discuss the potential of oriented arrangement
for determination of the directionally resolved magnetization relaxation using stroboscopic SANS and TISANE.
[1]
[2]
[3]
[4]
[5]
[6]
G. M. Whitesides, B. Grzybowski, Science 295, 2418 (2002).
J. Chen et al., Nano Lett. 10, 5103 (2010).
S. Polarz, Adv. Funct. Mater. 21, 3214 (2011).
A. Wiedenmann et al., Phys. Rev. B 84, 214303 (2011).
S. Disch, E. Wetterskog et al., Nano Lett. 11, 1651 (2011).
S. Disch et al., submitted (2012).
P.174 Weak ferromagnetism with giant canting in a chiral transition metal network
R Feyerherm1, S Landsgesell1, S Süllow2 and J Litterst2
1
Helmholtz-Zentrum Berlin, Germany, 2TU Braunschweig, Germany
Weak ferromagnetism due to spin canting is considered to be an effective approach in the quest for molecule-based
magnets [1]. Even if the interactions between the magnetic centres are dominantly antiferromagnetic, a
magnetically ordered state may exhibit spontaneous magnetization due to the Dzyaloshinskii-Moryja (DM)
interaction or single-ion anisotropy. The former usually causes only small canting (< 1°) between neighbouring
magnetic moments. Considering single ion anisotropy, staggering of the local magnetic easy directions at
neighbouring magnetic centres may produce much larger spin canting. The maximum possible staggering of easy
directions is 90°. This is indeed realized, e.g., in the chiral three-dimensional (3D) network 3D-Fe(N3)2(4,4'-bpy),
where bpy = bipyridine. This compound has been reported to exhibit a "ferromagnetic-like" transition at 20 K
suggesting antiferromagnetic ordering with large canting [2].
Based on combined neutron diffraction and 57Fe Mössbauer spectroscopy data, we demonstrate that in this
compound the interplay between antiferromagnetic exchange and single ion anisotropy leads to weak
ferromagnetism with a giant spin canting angle of θ = 20°. At 1.6 K the total ordered moment is μ = 3.9(1) μB,
resulting in an extremely large ferromagnetic component, μF = 1.4 mB.
[1]
[2]
D.-F. Weng, Z.-M. Wang and S. Gao, Chem. Soc. Rev. 40, 3157 (2011)
A. Fu, X. Huang, J. Li, T. Yuen, C. L. Lin, Chem. Eur. J. 8, 2239 (2002)
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P.175 Magnetization-reversal study of Co nanorod arrays by small-angle neutron scattering
A Günther1, D Honecker1, J-P Bick1, U Keiderling2, A Tschöpe3, R Birringer3 and A Michels1
1
University of Luxembourg, Luxembourg, 2Helmholtz Zentrum Berlin, Germany, 3Universität des Saarlandes, Germany
Pulsed electrodeposition of Cobalt into a nanoporous aluminum oxide layer results in an ordered Co nanorod array.
The nanorods with typical diameter d ≈ 30 nm and length l between 200 and 400 nm are hexagonally arranged
with a center-to-center distance of the rods of dcc ≈ 40 nm. Such an array can be considered as a model system for
a ferromagnetic nanorod arrangement. In order to study the magnetization-reversal process of these arrays we used
magnetic-field-dependent small-angle neutron scattering (SANS), since it allows one to probe the relevant length
scales of the magnetic microstructure. Via Fourier back-transformation of the magnetic SANS data we determined
the autocorrelation function C(r) and the characteristic correlation length lC of the spin-misalignment in the rods. In
particular, our results show that the correlation length lC is a sensitive measure to analyze the magnetization-reversal
process of the nanorod array.
P.176 Investigation of the Magnetic Structures of Hexagonal FeMnP1-xSix (0.25 ≤ x ≤ 0.50) by Powder Neutron
Diffraction
V Höglin1, M Hudl2, M Sahlberg1, P Beran3, M Sørby4, P Nordblad2 and Y Andersson1
1
Department of Chemistry - Ångström, Uppsala University, Sweden, 2Department of Engineering Sciences, Uppsala
University, Sweden, 3Nuclear Physics Institute, Academy of Sciences of the Czech Republic, 4Physics Department,
Institute for Energy Technology, Norway
Magnetic refrigeration systems (utilizing the magnetocaloric effect) are uprising energy savers with high demands on
its functional working materials. Materials with tunable magnetic parameters are therefore favorable to achieve
desired magnetocaloric properties (Curie temperature (Tc) near room temperature, large magnetic entropy change
(ΔSM), cheap and non-toxic elements).
A powder X-ray and neutron diffraction investigation has been performed to study how the Si concentration
influences the crystal and magnetic structure in the hexagonal region of FeMnP1-xSix (0.25 ≤ x ≤ 0.50). Samples
were prepared using the Drop Synthesis Method and are crystallized in the hexagonal Fe2P-type structure (P-62m).
Magnetic measurements show a tunable Tc which varies from 250 K at x = 0.25 to 382 K at x = 0.50. The magnetic
moments in the ferromagnetic structure of x = 0.50 are aligned in the basal plane of the hexagonal unit cell while it
is possible that the moments of x = 0.25 are disoriented from the hexagonal hard axis. In agreement with the similar
compound FeMnP0.70As0.30 where the moments in are aligned with a shift of 50±20° from the hard axis [1, 2]. Our
results present a material system with promising properties for use in a magnetic refrigeration system due to its
easily tuned magnetic properties and rather good magnetocaloric effect.
[1]
[2]
M. Bacmann et al, J. Magn. Magn. Mater.134 (1994) 59–67
R. Zach et al, J. Magn. Magn. Mater.147 (1995) 201–204
P.177 Theory of magnetic small-angle neutron scattering of two-phase ferromagnets
D Honecker and A Michels
University of Luxembourg, Luxembourg
Based on micromagnetic theory we have derived analytical expressions for the magnetic small-angle
neutron scattering (SANS) cross section of a two-phase particle-matrix-type ferromagnet. The
approach—valid close to magnetic saturation—provides access to several features of the spin structure
such as perturbing magnetic anisotropy and magnetostatic fields. Depending on the applied
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magnetic field and on the magnitude of the magnetic anisotropy field relative to the magnitude
of the jump in the longitudinal magnetization at the particle-matrix interface, we observe a variety
of angular anisotropies in the magnetic SANS cross section. In particular, the model explains
the “clover-leaf”-shaped angular anisotropy which was previously observed for several nanostructured
magnetic materials, and it provides access to the magnetic interaction parameters such as the
exchange-stiffness constant.
P.178 Magnetic dynamics of mesoporous hematite
H Jacobsen1, A Hill2, R Stewart3, F Jiao4, H Mutka5, A Harrison5 and K Lefmann6
1
Niels Bohr Institute, Denmark, 2Formerly at The European Synchrotron Radiation Facility, France, 3Science and
Technology Facilities Council, Rutherford Appleton Laboratory, UK, 4Center for Catalytic Science & Technology,
Department of Chemical Engineering, USA, 5The Institute Laue-Langevin, France, 6Nanoscience Centre, Niels Bohr
Institute, University of Copenhagen, Denmark
Samples of nanoscale hematite, with different surface geometries and properties have been studied with inelastic
time-of-flight neutron scattering. 15 nm diameter nanoparticles previously shown to have two collective magnetic
excitation modes in separate triple-axis neutron scattering studies have been studied in further detail using the
advantage of a large detector area, high resolution and large energy transfer range of the IN5 TOF spectrometer. A
mesoporous hematite sample has also been studied, showing similarities to that of the nanoparticle sample and
bulk hematite. Analysis of these modes provides temperature dependance of the anisotropy coefficient of the caxis. This is shown to remain negative throughout the temperature range studied in both samples, providing an
explanation for the previously observed suppression of the Morin transition in the mesoporous material. The values
of this anisotropy coefficient are found to lie between those of bulk and nano-particulate samples, showing the
hybrid nature of the mesoporous 3-dimensional structure
P.179 Neutron scattering investigations on magnetic metal-oxide BiMn0.5Fe0.5O3 and rare-earth-nitride thin films
F Klose1, D Cortie2, S Brueck3 and T Saerbeck4
1
ANSTO, Australia, 2University of Wollongong, Australia, 3University of New South Wales, Australia, 4University of
Western Australia & ANSTO Australia,
We will present neutron scattering investigations on two materials with potential in spintronics or related
applications, BiMn0.5Fe0.5O3 metal-oxide films and Rare-Earth-nitride films (RE: Dy, Er and Ho). BiMn0.5Fe0.5O3 is
interesting due to its possible multiferroicity while the RE-N family contains members which are half-metallic
ferromagnets or ferromagnetic semiconductors that are interesting for spin injection.
1. BiMn0.5Fe0.5O3 thin films
High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline
BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive
magnetic properties that differentiate it from both parent compounds: BiFeO 3 and BiMnO3. A transition to long-range
G-type antiferromagnetism was observed below 120 K with a (1/2, 1/2, 1/2) propagation vector. A weak
ferromagnetic behavior was measured at low temperature by SQUID magnetometry (D. L. Cortie et al., App. Phys.
Lett. 101 (2012) 172404 ).
2. Rare-Earth-nitride thin films
Polarised neutron and X-ray reflectometry were used to determine the nanoscale magnetic and chemical depth
profile of the heavy Rare-Earth-nitrides HoN, ErN and DyN. The magnetic moment per Rare-Earth ion was
determined by PNR as function of temperature in the range 5 - 50 K, at fields 1 - 3 T. A clear ferromagnetic
ICNS 2013 International Conference on Neutron Scattering
remanence is seen for DyN at low temperature. SQUID magnetometry was used to determine the temperature and
field dependence of the magnetic moment of HoN. The magnetic moments for all rare-earth nitrides studied are
significantly lower than expected relative to the predictions of density-functional-theory and Hund's rules for these
4f ionic materials.
P.180 Investigation of internal magnetic structure of an amorphous microwire using polarized neutron microbeam
S Kozhevnikov1, F Ott2, J Torrejón3, M Vàzquez4 and A Thiaville3
1
JINR, Russia, 2CEA/CNRS, IRAMIS, Laboratoire Léon Brillouin, France, 3Laboratoire de Physique des Solides,
Université Paris-sud, France, 4Instituto de Ciencia Materiales, CSIC, Spain
We present the application of polarized neutron microbeam of 2 µm width for the investigation of the internal
magnetic structure of microwire. The method of polarized neutron precession at transmission was used. The
microbeam was produced by tri-layer thin film (planar waveguide). The core-shell structure in an amorphous
CoFeSiB microwire of 190 μm diameter with ultrasoft magnetic behavior was investigated. This method may provide
a noticeable progress in the investigations of domain structures previously restricted by surface methods of
magnetometry.
P.181 Magnetic moment developed in the superconducting state of In nanoparticles measured by neutron
diffraction and magnetization
W-H Li, C-Y Li, C-H Lee, S K Karna and C-W Wang
National Central University, Taiwan
We report on the observation of a spontaneous magnetic moment developed in the superconducting state of an 18
nm In nanoparticle assembly. Superconductivity is clearly revealed below TC=3.45 K in the resistivity and ac
magnetic susceptibility measurements. Surprisingly, a spontaneous magnetization as large as 0.18 emu/g also
found to develop in the superconducting state. The magnetization begins to develop at a temperature that is slightly
but noticeably lower than the development of superconductivity and this component disappears in the normal state,
signaling that superconductivity triggers the development of spontaneous magnetization. The existence of an
intrinsic magnetic moment in the superconducting state is confirmed by neutron diffraction measurements. The
widths of the magnetic peaks are the same as those of the nuclear ones, indicating that the magnetic moments are
distributed throughout the whole nanoparticle, rather than are located solely on the surface. The magnetic moment
developed in the superconducting state is <μZ>=0.066 μB. Possible mechanisms will be discussed.
P.182 Isothermal switching of exchange bias effect in DyCo/NiFe bilayers
D Lott1, K Chen1, V Lauter2, K Dyadkina3, F Radu4, R Abrudan4 and A Schreyer1
1
Helmholtz-Zentrum Geesthacht, Germany, 2Oak Ridge National Laboratory, USA, 3Petersburg Nuclear Physics
Institute, Russia, 4Helmholtz-Zentrum Berlin, Germany
Alloys of rare-earth elements and 3d transition metals became recently again in the focus of attention due there rich
variety of magnetic effects owed to the different anisotropies of both material classes [1, 2]. Here, an extraordinary
high in-plane exchange bias up to 40 mT was found at room temperature throughout a whole hard ferrimagnetic
layer of DyCo coupled to a NiFe layer. Particularly interesting is that the exchange bias effect is achieved by
magnetizing the DyCo layer in the perpendicular direction in respect to the film plane and its direction can be
switched by alternation of the direction of the perpendicular magnetic fields in relative moderate fields of about
200mT. Detailed polarized neutron reflectometry (PNR) measurements were carried out to investigate the underlying
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mechanism behind the extraordinary effect and will be discussed here in the context to complementary
measurements using the magnetic optical Kerr effect (MOKE) and X-ray magnetic circular dichorism (XMCD).
[1]
[2]
S. Mangin, T. Hauet, Y. Henry, F. Montaigne and E.E.Fullerton, Phys. Rev. B, 74, 0244414 (2006)
F. Radu, R. Abrudan, I. Radu, D. schmitz H. Zabel, Nat. Communications, 3, 715(2012)
P.183 Magnetic neutron scattering on nanomagnets: Decrypting cross-section images using micromagnetic
simulations
A Michels1, S Erokhin2, D Berkov2 and N Gorn2
1
University of Luxembourg, Luxembourg, 2INNOVENT Technology Development, Germany
We have used numerical micromagnetics for the calculation of the magnetic small-angle neutron scattering (SANS)
cross sectionof two-phase nanocomposites. In contrast to neutron experiments, in which one generally measures
only a weighted sum of the Fourier components of the magnetization, our approach allows one to study the behavior
of the individual contributions to the total scattering. Results for the unpolarized SANS cross section as well as for
the spin-flip SANS will be discussed. The procedure furnishes unique and fundamental information regarding the
magnetic microstructure and corresponding magnetic scattering from nanomagnets. In particular, our simulations
explain the recent observation of magnetodipolar correlations in two-phase nanocomposites and, moreover, suggest
their relevance for a wide range of magnetic materials such as nanocomposites, nanoporous magnets, and
magnetic recording media.
[1]
[2]
S. Erokhin, D. Berkov, N. Gorn, and A. Michels, Phys. Rev. B 85, 024410 (2012)
S. Erokhin, D. Berkov, N. Gorn, and A. Michels, Phys. Rev. B 85, 134418 (2012)
P.184 Exchange coupling in NixCu100-x films of various thickness
B Nagy1, Y N Khaydukov2, L F Kiss1, A Sulyok3, S Sajti1, D G Merkel1, F Tanczikó1, A S Vasenko4 and L Bottyán1
1
Wigner Research Centre for Physics, Hungarian Academy of Sciences, Hungary, 2Max-Planck Institute for Solid
State Research, Germany, 3Research Centre for Natural Sciences, Institute for Technical Physics and Materials
Science, Hungary, 4Institut Laue-Langevin, France
Recent interest in the magnetism of ultrathin films and multilayers is driven by their perspective applications in the
magneto-electronics as sensors or information storage devices. A particularly interesting field in this respect is the
superconductor/ferromagnet (S/F) proximity effect. In such heterostructures with weak F layer in contact with a S
layer the so-called cryptoferromagnetic state was predicted[1]. The aim of this study was to provide valuable
information for fabrication of samples with controlled exchange coupling strength for studies of S/F proximity
effects.
In this study the thickness (dF) and concentration (x) dependence of the Curie temperature of NixCu100-x(dF)
ferromagnetic alloy layers (x = 55, 65, dF = [3 nm ÷ 12 nm]) being in contact with a V layer was studied. When the
thickness is comparable to that of the mixed V/F interface region, we have found that the Curie temperature
increased with the thickness of the F layer. At larger thicknesses our results reflected the reported bulk values[2].
The strong layer thickness dependence of the Curie temperature cannot be explained by a direct finite-size effect.
Therefore a proximity-coupled bilayer model of the V/NixCu100-x mixed interface is invoked, which provides a small
ratio of the Fermi-level densities of states resulting in a weak coupling between the transition and the unaffected
part of the ferromagnetic layer. The Curie temperatures were measured with SQUID magnetometry, and the interface
layer was characterized with the help of neutron reflectometry and Auger-electron spectroscopy.
[1]
[2]
P. W. Anderson and H. Suhl, Phys.Rev. 116, 898 (1959)
I. Bakonyi et al., J. Phys. - Cond. Matter 11, 963 (1999)
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P.185 Magnetic proximity effect at Fe/V, ferromagnet/superconductor interface revealed by neutron reflectometry
B Nagy1, Y N Khaydukov2, L F Kiss1, A Csik3, J Kim2, T Keller2, R Steitz4 and L Bottyán1
1
Wigner Research Centre for Physics, Hungarian Academy of Sciences, Hungary, 2Max-Planck Institute for Solid
State Research, Germany, 3Institute of Nuclear Research of the Hungarian Academy of Sciences,
Hungary, 4Helmholtz-Zentrum Berlin für Materialien und Energie, Germany
Superconductor/ferromagnet (S/F) interfaces attracted growing interest over the last years, because of the wide
range of exhibited interesting phenomena that include spin valves and π-Josephson junctions[1]. One of these is
the magnetic proximity effect, the manifestation of a magnetic layer in the superconductor at the interface, was
predicted[2]and later measured[3]on a single F/S bilayer.
Polarized neutron reflectometry is an ideal tool to investigate this phenomenon, since it is not only able to
investigate the magnetic moment of the system, but also capable of determining the depth distribution of the
induced moment. Since the predicted magnetic signal from one layer is too weak, and with preparing multiple
layers the problem of cumulative roughness of the interfaces arises, one needs to apply special techniques to study
such effect.
In this work we prepared Fe/V bilayer as the model system, and used neutron waveguide enhancement[4]and spinasymmetry analysis for evaluating the collected data. The samples were characterized by SQUID magnetometry,
four point AC resistivity experiments and SNMS measurements. From the collected data, we have derived that below
the superconducting transition temperature the overall magnetic moment of the system is increased. And by
modeling the spin-asymmetry of the system we concluded that a new magnetic layer with exponentially decaying
magnetization appeared in the superconductor near the interface.
[1]
[2]
[3]
[4]
A. I. Buzdin, Rev. Mod. Phys. 77, 935 (2005)
M. Yu. Kharitonov et al., Phys. Rev. B 73, 054511 (2006)
R. I. Shalikov et al., Phys. Rev. B 80, 214523 (2009)
Yu. N. Khaydukov et al., Crystallogr. Rep. 55, 1235 (2010)
P.186 Neutron diffraction and optical studies on antiferromagnetic Na and K nanoclusters incorporated into
sodalite
T Nakano1, A Hanazawa1, M Matsuura2, K Watanabe1, K Hirota3 and Y Nozue1
1
Department of Physics, Osaka University, Japan, 2Institute for Materials Research, Tohoku University,
Japan, 3Department of Earth and Space Science, Osaka University, Japan
Various kinds of magnetic orderings have been found in alkali-metal clusters arrayed in zeolite crystals. They are
novel magnetic materials because they contain no magnetic element and the magnetic orderings are realized by selectrons confined in the regular nanospace of zeolites. Sodalite is a kind of zeolites where cages with the inner
diameter of 0.7 nm are arrayed in a bcc structure. Na43+ and K43+ clusters arrayed in sodalite are known to show
antiferromegnetism (AFM) below TN of 48 K and 72 K, respectively. The cluster accommodates an unpaired selectron shared by four cations in the cage. We performed neutron diffraction (ND) measurements and succeeded in
observing the magnetic Bragg peaks [1]. This is the first direct observation of long range ordering in s-electron
systems by using ND. The AFM order is given by the antiparallel coupling of the spins in the body center and the
corner clusters. The magnetic form factor coincides well with the s-electron wave function confined in the
nanometer-sized cage. It is also found that the form factor dumps quicker in K clusters than that in Na ones as a
function of Q. We also measured optical reflection spectra. A significant red shift is observed in s-p transition in the
K clusters. These results clearly indicate that the wave function of K cluster is larger than that of Na cluster. This
leads to a decrease in U/t and the increase in TN in the Mott-Hubbard picture.
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[1]
T. Nakano et al., Phys. Rev. Lett. 109, 167208 (2012)
P.187 Exchnage biased LSMO/YMO bilayers
A Paul and P Böni
TUM, Germany
Using polarized neutron reflectometry we have investigated the magnetic proximity effect in epitaxial bilayer
heterostructures comprising of ferromagnetic La{0.7}Sr{0.3}MnO{3} (LSMO) and antiferroamgnetic YMnO{3} (YMO) layers.
[1] We find the unusually large 'vertical shift' of the hysteresis loop along the magnetization axis is grossly related
to an intermixed layer at the LSMO-YMO interface instead of the usually believed antiferromagnetic layer alone. We
show the detailed magnetic depth profile at the interface in elucidating the intrinsic nature of the vertical shift.
[1]
Journal of Magnetism and Magnetic Materials 323 (2011) 2892
P.188 Structural and magnetic correlations in self-assembled nanoparticle superlattices
O Petracic1, E Josten1, A Glavic2, U Ruecker1, H Ambaye2, V Lauter2, S Mattauch3, A Klapper1, E Wetterskog4, G
Salazar-Alvarez4, L Bergström4 and T Brückel1
1
Jülich Centre for Neutron Science JCNS-2 and Peter Grünberg Institute PGI-4, Germany, 2Quantum Condensed
Matter Division, Spallation Neutron Source, Oak Ridge National Laboratory, USA, 3Jülich Centre for Neutron Science
JCNS, Forschungszentrum Jülich GmbH, Germany, 4Department of Materials and Environmental Chemistry,
Arrhenius Laboratory, Stockholm University, Sweden
Nanoparticle superlattices are a novel type of material with tunable electronic, optical and magnetic properties.
Their building blocks are nanoparticles from a metallic, metal-oxide, or semiconducting material. We report about
the structural and magnetic properties of self-assembled superlattices of Fe2O3 nanoparticles. The particles are
cubes of 10 nm size. The lateral ordering is quantified using electron microscopy and grazing incidence small angle
X-ray scattering (GISAXS). The nanoparticles form well-ordered 3-dimensional 'mesocrystals' with bct or fcc
symmetry and relatively large structural correlation lengths of 2-10 𝜇m when deposited onto Silicon substrates.
Magnetostatic interactions between the nanoparticles give rise to collective ordering phenomena. The magnetic
inter-particle correlations are investigated by polarized grazing incidence small-angle neutron scattering (GISANS)
and compared to numerical simulations. Research at Oak Ridge National Laboratory’s Spallation Neutron Source
was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.
P.189 Magnetic behavior of MnO nanoparticles -a detailed study using magnetometry and neutron scattering
X Sun1, A Klapper1, O Koehler2, H Bauer2, W Tremel2, K Nemkovski3, Y Su3, O Petracic1 and T Brückel1
1
Jülich Centre for Neutron Science JCNS-2 und Peter Grünberg Institut PGI-4, Forschungszentrum Jülich GmbH,
Germany, 2Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität Mainz,
Germany, 3Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Germany
Antiferromagnetic monodisperse MnO nanoparticles with various diameters (6-20nm) have been studied using
magnetometry and polarized neutron diffraction. Although MnO particles have often been studied before, the
surprising magnetic signature as found in zero field cooled (ZFC)/field cooled (FC) magnetization curves remained
unclear. It was usually attributed to either core-shell or superparamagnetic behavior. To shed light on the magnetic
behavior in MnO nanoparticles we have measured ZFC/FC at various magnetic fields, hysteresis curves and
thermoremanent (TRM)/ isothermoremanent (IRM) curves using SQUID magnetometry. The results are compared to
polarized neutron scattering experiments at various temperatures obtained on the DNS instrument (FRMII,
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Garching). Various explanations in terms of core-shell, superparamagnetic, 'antiferro-superparamagnetic' or
antiferromagnetic domain-state behavior are discussed.
P.190 Synthesis of Ga1+xFe1-xO3 nanoparticles by Sol-Gel method and the characteristics of their chemical and
magnetic ordering
K Recko1, U Wykowska2, G André3, W Olszewski1, J Waliszewski1, D Satuła1 and K Szymański1
1
Faculty of Physics, University of Bialystok, Poland, 2Institute of Chemistry, University of Bialystok,
Poland, 3Laboratoire Léon Brillouin, CEA-Saclay, France
The multiferroic GaFeO3 has been recently studied for its potential applications. The structural and magnetic
properties of the system depend strongly on the method of preparation. Thus many efforts have been made on
fabrication of gallium iron oxide by the Sol-Gel (SG) method. The gallium iron oxide (GFO) crystallizes in an
orthorhombic crystal structure. The crystallographic unit cell contains 4 cation sites and 6 oxygen anion sites all in
general position (4a) of the Pc21n space group (no. 33). In the perfectly ordered structure sites labeled by Ga(1),
Ga(2), and Fe(1), Fe(2) are entirely occupied by Ga3+ and Fe3+ ions, respectively. The magnetic ground state of a
perfectly ordered GaFeO3 structure was determined by electronic structure calculations including spin-orbit
interactions. The system forms a collinear antiferromagnetic ordering along c direction with the calculated magnetic
moment of irons equal to µFe1 = 4.27 µB and µFe2 = –4.34 µB, respectively. Any disorder of the cations origin
leads to more complicated structures. In the light of neutron and Mössbauer measurements the strong correlation of
the magnetic ordering against the cation distribution among the four sites has been proven. Starting from
ferromagnet to canted antiferrimagnet, the several models of the commensurate magnetic structures of GFO have
been tested. In spite of 26(5)% content of Fe2O3, the analysis revealed that GaFeO3 prepared by SG method,
exhibits a ferrimagnetic order with spins almost parallel to the c-axis. The values of the total magnetic moments of
µFe=3.8(2) µB at 1.8 K are lower than predicted by theory, what can be caused by the presence of iron atoms in
the Ga sities.
P.191 In search of the origin of the long-range magnetic ordering of Magnetic Ionic Liquids based on imidazolium
cation and tetrachloroferrate anion
G Saiz1, M de Pedro1, P Migowski2, O Vallcorva3, J Junquera4, J A Blanco5, J A Gonzalez6, J Rius3 and J R Fernandez7
1
CITIMAC & MAGMA, Unidad Asociada-CSIC, University of Cantabria, Spain, 2Universidade Federal do Rio Grande
do Sul, Spain, 3Institut de Ciència de Materials de Barcelona (CSIC), Spain, 4CITIMAC, University of Cantabria,
Spain, 5Departamento de Física, Universidad de Oviedo, Spain, 6MALTA Consolider Team, DCITIMAC, Facultad de
Ciencias Universidad de Cantabria, Spain, 7CITIMAC & MAGMA,Unidad Asociada-CSIC, Universidad de Cantabria,
Spain
Magnetic ionic liquids (MILs) are promising new materials that allow adding further features to the typical properties
of ionic liquids such as magnetic, photophysical/optical, or electrochromic behavior that are due to the
incorporated metal ions. These MILs are single component materials with unpaired electrons in the valence shell of
the metal cation that show a strong response to external magnetic fields in the liquid state. In consequence, there is
a strong interest in how these MILs can be designed by choosing the right cation-anion combination. The question
about cooperative magnetic effects, complex anion interaction, and magnetostructural correlation is quite important
and it is actually in focus of materials science. These aspects could be explained connecting the experimental and
computational studies in [Dimim][FeCl4],a new MIL with a long-range magnetic ordering below melting point.
The initial magnetic study of [Dimim][FeCl4], using magnetic and heat capacity measurements, displayed an
antiferromagnetic ordering below TN =6K. High resolution NPD study on D2B was used to obtain the crystal structure
of this MIL at room temperature. Temperature dependent NPD study on D1B enabled the magnetic structure and
solid-solid transition to be determined throughout the entire temperature region of interest. The magnetostructual
ICNS 2013 International Conference on Neutron Scattering
correlations show that the formation of chlorine bridges allows the antiferromagnetic coupling, including two
diamagnetic intermediaries. The results have been confirmed with computational studies displaying a large spindensity delocalization toward the chlorine atoms, which explains the efficiency of the superexchange pathways in
transmitting the magnetic interaction.
P.192 Depth dependent structure and magnetization of bi-nuclear (Co-Fe)-phthalocyanine films
S Singh1, A Singh2, M R Fitzsimmons3, S Samanta2, S Basu1 and D K Aswal2
1
Solid State Physics Division, Bhabha Atomic Research Center, India, 2Technical Physics Division, Bhabha Atomic
Research Center, India, 3Los Alamos National Laboratory, USA
Organic functional molecules on solid surfaces have been extensively investigated with regard to both the
fundamental aspects of the organic–inorganic interface and potential applications in spintronics and molecular
electronics. Transition-metal phthalocyanines (TMPcs) are archetypal organic semiconductors and their attractive
properties are already being extensively exploited in technological application such as dyes, light emitting diodes,
solar cells, field effect transistors, gas sensors, field emission applications and single molecule devices.
Using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR) we measured the depth dependent structure
and magnetization of pure and bi-nuclear films of iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc)
grown on sapphire substrate. Our PNR data indicate that the bi-nuclear phthalocyanine film (Co-Fe)Pc show a long
rage magnetic ordering with a magnetization of 40 ± 15 emu/cm3 at 10 K. Whereas the pure film of FePc and CoPc
show negligible magnetization at 10 K. The net magnetization on (Co-Fe)Pc film may be attributed due to possible
change in structural properties of the film as compared to pure film as suggested by XRR measurements.
P.193 The Magnetic contribution to the heat capacity of Co3O4 nanoparticles
E Spencer1, N Spencer1, B Woodfield2, S Parker3, A Kolesnikov4 and A Navrotsky5
1
Virginia Tech, USA, 2Brigham Young University, USA, 3STFC Rutherford Appleton Laboratory, UK, 4Oak Ridge
National Laboratory, USA, 5University of California at Davis, USA
INS methods represent a novel way of examining the thermodynamic properties of metal-oxide materials at the
nanoscale. Low temperature (11 K) INS data for two hydrated nanoparticle systems, namely, 10 nm CoO·0.10H2O
and 16 nm Co3O4·0.40H2O will be presented, and from these data the isochoric heat capacity and vibrational
energy for the hydration layers confined to the surface of these nanoparticle systems have been determined. The
results show that water on the surface of CoO nanoparticles is more tightly bound than water confined to the surface
of Co3O4, and this is reflected in the reduced heat capacity and vibrational entropy for water on CoO relative to water
on Co3O4 nanoparticles. This supports the trend, seen previously by calorimetry, that water is more tightly bound in
materials with higher surface energies.
We will also show that the INS spectra for the antiferromagnetic Co3O4 particles has a sharp and intense magnetic
excitation at 5 meV, and how from this peak the magnetic contribution to the heat capacity of Co3O4 nanoparticles
can be calculated. This represents the first example of use of INS data for determining the magnetic contribution to
the heat capacity of any magnetic nanoparticle system.
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P.194 Depth-dependent distribution of magnetic moments in [La2/3Sr1/3]n±1MnnO3n±1/SrTiO3
A Steffen1, S Pütter1, S Mattauch1, W Zander2, J Schubert2 and T Brückel3
1
Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Germany, 2Peter Grünberg Institut PGI, ,
Germany, 3Jülich Centre for Neutron Science JCNS and Peter Grünberg Institut PGI, JCNS-2, PGI-4: Scattering
Methods, Germany
Transition metal oxide thin films give rise to a huge variety of fascinating phenomena like ferromagnetism at
interfaces of non-magnetic materials as found in SrTiO3/KTaO3[1]. To analyze these effects quantitatively a well
defined layer structure is needed to relate macroscopically gained properties to microscopic structure probed via
synchrotron or neutron scattering. By molecular beam epitaxy (MBE) high quality epitaxial films can be achieved
with high purity, low intrinsic defect concentrations and atomic-layer control. The stoichiometry within the films may
be varied easily.
Due to its high Curie temperature of 350K and its nearly perfect spin polarisation La2/3Sr1/3MnO3 (LSMO) is under
intense investigation. Thin films on top of SrTiO(STO) show an inhomogeneous magnetization[2]. On the contrary to
the intensively investigated different Sr doping levels in La1-xSrxMnO3 we focused on different [La/Sr] to Mn ratios to
investigate representations of the Ruddlesden-Popper manganite series [La2/3Sr1/3]n±1MnnO3n±1 to compare the
magnetic characteristics.
At the polarized neutron reflectometer TREFF@FRM II we determined the magnetic depth profile of
[La2/3Sr1/3]2Mn3O8/ STO and [La2/3Sr1/3]3Mn2O7/STO and compared these results with LSMO/STO. The samples were
grown utilizing our oxide MBE setup which is located at the FRM II. The stoichiometry was adjusted in-situ via quarzcrystal balance and crosschecked with RBS while the growth mode was monitored via RHEED. By LEED, XRR and
XRD, the crystalline sample quality was studied. The magnetic properties were determined via SQUID
magnetometry.
[1]
R. Oja et al., Phys. Rev. Lett. 109, 127207 (2012); [2] F. Ott, J. Phys.: Condens. Matter 20, 264009
(2008)
P.195 The magnetic depth profile of high-quality Fe3O4/ZnO heterostructures determined by Polarised Neutron
Reflectometry
N-J Steinke1, M Zapf2, O Kirilmaz2, S Brueck2, N Tarakina3, M Kamp3, E Goering4, J Cooper1, C Kinane1, M Sing2 and
R Claessen2
1
ISIS, UK, 2Physikalisches Institut, Universität Würzburg, Germany, 3Technische Physik, Universität Würzburg,
Germany, 4Max Planck Institute for Intelligent Systems, Germany
Magnetite (Fe3O4) thin films have recently attracted large interst due to their potential use as a spin-injector into
semiconducting hosts. However, for successful spin-injection the interface properties, and in particular the magnetic
state near the interface is crucially important. Here we present an investiagtion of epitaxial, MBE grown Fe3O4/ZnO
heterostructures. X-ray photoelectron spectroscopy shows that the samples are phase-pure and nearly
stochiometric.
To gain detailed information on the magnetic depth profile polarised neutron reflectometry (PNR) measurements
were performed. These measurements were complimented by X-ray reflectometry, SQUID magnetometry and
transmission electron microscopy. While the structural profile of the samples was good, the PNR measurments
revealed a several nanometer thick region of reduced magnetisation near the ZnO interface. This is likely to have a
strong effect on the spin-injection efficiency of Fe3O4 on ZnO. The measurements suggest a distinct difference in
film quality depending on substrate termination in our samples.
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P.196 Polarized neutron reflectivity studies of the magnetic depth profile of a Ni 80Fe20/Mn exchange bias multilayer
with large enhanced orbital magnetic moments
H Su1, M Huang1, H Lin1, K Lin2, F Close3, T Lan2, C Lee4, D Cortie5 and Y Khaydukov6
1
National Synchrotron Radiation Research Center, Taiwan, 2Department of Materials Science and Engineering,
National Chung Hsing University, Taiwan, 3Australian Nuclear Science and Technology Organisation, Australia,
4
National Synchrotron Radiation Research Centre & National Tsing Hua University, Taiwan, 5Australian Nuclear
Science and Technology Organisation & The University of Wollongong, Australia, 6Max-Planck Institute for Solid
State Research, Germany
Polarized neutron reflectivity (PNR) is an excellent tool for magnetic thin film research and has been used to
characterize the correlation between chemical interface structure and enhanced interfacial magnetic moments in
multilayer systems [1]. Our previous x-ray spectroscopy study of a Ni80Fe20/Mn multilayer [2] found a link between
the exchange bias and pinned interfacial orbital moments in an uncompensated antiferromagnetic (AFM) layer. This
report indicates a connection between spin-orbit coupling at the AFM/FM interface and the resulting unidirectional
anisotropy, elucidating the interplay of the interfacial exchange coupling in the Py/Mn multilayer system and the
large enhanced orbital magnetic moment [2]. The orbital magnetic moments of Fe and Ni are enhanced from
17.0% to 25.0% and 11.0% to 17.0%, respectively from 300K to 28K. The observed exchange bias is also
increased from 1.0 Oe to -77.0 Oe at these temperatures. Other papers have suggested that the enhanced orbital
magnetic moment in similar systems was induced by the magnetic interface roughness [3-4]. We will present PNR
data and analyze the magnetic depth profile of this sample system. Temperature dependent PNR will help to clarify
the magnetic interface effects between Py and Mn layers that generate the enhancements of the orbital magnetic
moments. In light of the PNR data, we will discuss various possible scenarios including the development of
magnetic roughness, bi-quadratic coupling and the possibility of a dead magnetic layer [4] at the interfaces to
compare with the our previous XMCD results.
[1]
[2]
[3]
[4]
M.R. Fitzsimmons et al, J. Magn. Magn. Mater., 271 (2004) 103
H. C. Su et al, Phys. Rev. B 87 (2013) 014402
M. Z. Lin et al, Surf. Sci. 601 (2007) 5707
H. C. Su et al, Physica B 357 (2005) 80
P.197 Behaviour of a Ni rich Ni/Al multilayer on annealing
M Swain, S Singh, D Bhattacharya, M Gupta and S Basu
Bhabha Atomic Research Center, India
Intermetallics of nickel and aluminum are technically important because of their desirable properties viz. low
density, high melting point and good oxidation resistance. We have studied the effect of annealing on depth
dependent structure and magnetic properties of Ni/Al multilayer [Ni(200Å)/Al(100 Å)]×5 grown on Si substrate
using ion beam sputtering. The system was annealed at 200°C in vacuum ( 10-5 mbar). The as-deposited and the
annealed multilayer was characterized using Polarized Neutron Reflectometry (PNR), X-ray Reflectivity (XRR), X-ray
diffraction (XRD) and Secondary Ion Mass Spectroscopy (SIMS). The interface structure of film inferred from
reflectivity data is consistent with SIMS results. The XRD confirms that the Ni and Al layers were crystalline in the
as-deposited sample. The nuclear scattering length density profile and magnetic density profile of the as deposited
and annealed sample were obtained by fitting the PNR data. Evidence for diffusion of Al layers was seen in SIMS
while the Ni layers still remained intact after annealing. Thin alloy layers of around 10 Å to 20 Å thickness were
identified at the interfaces from the reflectivity measurements. But the periodic multilayer structure of the system
remains intact even after annealing. This shows the stability of the Ni rich system against annealing. The PNR data
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also shows a slight reduction of the magnetic moment of the nickel atoms. This may be due to intermixing of the
non-magnetic Al atoms into the Ni layer.
P.198 Influence of additives (X= Al, Ti or Zr) on suppression of Fe and N self-diffusion in soft magnetic Fe-X-N thin
films
A Tayal1, M Gupta2, A Gupta2, M Horisberger3 and J Stahn3
1
UGC- DAE Consortium for Scientific Research, India, 2Paul Scherrer Institut, Switzerland
Iron nitrides are an important class of materials both from application and basic point of view. However, the thermal
stability of Fe-N compounds is rather poor due to weak Fe-N bonding. This can be accomplished with the fact that
the affinity of Fe for N is poor and the heat of formation (ΔH) for Fe-N is high. To overcome this, addition of third
element X (X = Al, Ti, Zr etc. having high affinity for N and low ΔH) was suggested to enhance the thermal stability of
Fe-N system. In the literature, it was argued that improved stability of the Fe-X-N should stem from the fact that in
presence of X, binding energy of system gets increased leading to suppression of Fe and N diffusion. However, this
has not yet verified experimentally. In the present work, we studied Fe and N self-diffusion in Fe-X-N (5 at.% of X=
Al, Ti or Zr) samples prepared using dc magnetron sputtering. Samples were characterized using x-ray diffraction,
Mössbauer spectroscopy and SQUID-VSM to study their structural and magnetic properties. Using polarized neutron
reflectivity (PNR), Fe and N self-diffusion was measured on isotopic multilayer ([Fe-N/57Fe-N] and [Fe-N/Fe-15N])
samples. It was found that films have nanocrystalline structure and are soft magnetic, also with addition of X the
structure and magnetic state of sample stabilizes. Using PNR, we measured self-diffusion of Fe and N and found
that both Fe and N diffusion is remarkably suppressed in presence of X. Obtained results can be understood in
terms of heat of formation of Fe-N/X-N and the affinity for N to Fe and X. In addition the role of grain boundary
precipitates in the form of X-N in improving the thermal stability of Fe-X-N films will also be discussed in present
work.
P.199 Thermal vibrations and static disorder in Chromium nanocrystals
D Wardecki, R Przeniosło and I Sosnowska
Faculty of Physics, University of Warsaw, Poland
Recent studies of displacement parameters, often called Debye-Waller factors for nanosized ferroelectric BaTiO3 [1]
and multiferroic BiFeO3 [2] have shown important influence of the thermal vibrations and static disorder on the
macroscopic properties of the material. In this study we present results for nanocrystal of pure chromium [3]. The
Debye-Waller parameters have been determined for nanocrystalline Cr (nano-Cr) and reference polycrystalline Cr by
using both neutron powder diffraction and synchrotron radiation based X-ray diffraction. The measurements were
performed as a function of temperature and the observed values of the Debye-Waller factors can be decomposed
into a temperature dependent part and a temperature independent part indicative of static disorder, defects and
microstrains. The present data was obtained with electrodeposited nano-Cr samples that were already studied
[4,5]. The present results are compared with similar studies of nano-Cr obtained by inert-gas condensation
techniques [6].
[1]
[2]
[3]
[4]
[5]
[6]
V. Petkov, S.M. Selbach, M.A. Einsarud, T. Grande and S.D. Shastri, et al. Phys. Rev. B78 (2008) 054107
V. Petkov, V. Buscaglia, M.T. Buscaglia, Z. Zhao and Y. Ren, Phys. Rev. Lett. 105 (2010) 185501
E. Fawcett, Rev. Mod. Phys. 60 (1988) 209
D. Wardecki, R. Przeniosło, A.N. Fitch, M. Bukowski and R. Hempelmann, J. of Nanoparticle Research 13
(2011) 1151-1161
D. Wardecki, R. Przeniosło, M. Bukowski, R. Hempelmann, A.N. Fitch and P. Convert, Phys. Rev. B86
(2012) 064410 1-5
J.A. Eastman and M.R. Fitzsimmons, J. Appl. Phys. 77 (1995) 522
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P.200 Size-induced and photoswitchable magnetic interplay between the core and shell components in nanoscaled Core/Shell Prussian blue compound RbCoFe/KNiCr
C-M Wu1, C-H Lee2, C-Y Li2and W-H Li2
1
National Synchrotron Radiation Research Center, Taiwan, 2National Central University, Taiwan
Abstract unavailable
P.201 RbxBayMn[3-(x+2y)]/2[Fe(CN)6]∙zH2O Prussian blue analogue: A possible switching between two magnetic states
S M Yusuf1, N Thakur1, M Medarde2 and L Keller2
1
Solid State Physics Division, Bhabha Atomic Research Centre, India, 2Paul Scherrer Institut, Switzerland
The current trend in the evergreen field of molecular magnetism is to investigate multifunctional materials e.g.
Prussian blue analogues (PBAs). In the present work, the nature of magnetic ordering in RbxBayMn[3(x+2y)]/2[Fe(CN)6]∙zH2O (x = 0.19, y = 0.3) PBA has been controlled by application of an external magnetic field (H). A
possible switching between two magnetic states, antiferromagnetic(AFM) and ferrimagnetic(FIM), upon application
of a weak H is proposed by employing dc magnetization and zero field neutron diffraction (ND) measurements. Field
dependent low temperature (T) ND measurements have been performed to gain a microscopic understanding of the
proposed AFM to FIM transition. Under zero field, the magnetic ordering is long-ranged AFM, consisting of an
antiparallel stacking of ferromagnetic sheets along crystallographic c-axis of its tetragonal crystal structure. Within
each sheet in ab plane, the ordered moments of Mn2+ and Fe3+ are aligned ferromagnetically along c-axis. Field
dependent ND study corroborates the AFM to FIM magnetic state switching. The FIM structure under external H
consists of antiferromagnetically coupled layers. Within each layer, Mn and Fe spins are antiparallel. The pure AFM
phase exists in a narrow T-H region. There is a broad region (in the T-H plane for 0<H≤4 Tesla) of coexisting AFM and
FIM phases. Above 4 Tesla, only FIM phase exists. An important finding is the presence of a tricritical point at the
meeting point of these three phases: AFM, FIM and paramagnetic. Such tunable PBAs which undergo controlled
changes of their molecular states in response to external perturbations may find applications in molecular
electronics.
P.202 Core–shell structure in “bare” La0.2Ce0.8CrO3 nanoparticles: Coexistence of sign reversal of both magnetization
and exchange bias field
S M Yusuf, P K Manna and M D Mukadam
Solid State Physics Division, Bhabha Atomic Research Centre, India
A tremendous effort is on for finding appropriate spintronics-materials that are suitable for practical applications.
We have observed an extraordinary coexistence of sign-reversal of both magnetization and exchange biasfield in the
multifunctional oxide nanoparticles of La0.2Ce0.8CrO3. A highly reversible bipolar-switching of magnetization, using
low applied magnetic fields (≤ 800 Oe), is demonstrated, which can be exploited in designing a volatile magnetic
memory element. The formation of the single phase (Orthorhombic: Pbnm) has been confirmed by the Rietveld
refinement analysis of the neutron diffraction patterns. The neutron diffraction study also establishes that the core of
the present nanoparticles is G-type antiferromagnetic. Whereas, the polarized neutronsmall angle scattering
(SANSPOL) study shows the presence of a magnetic scattering which arises from the shell part of the nanoparticles
due to disordered surface-spins. The analysis of the SANSPOL data shows that these nanoparticles have a mean
core diameter of 12.3±1.1 nm, and a shell thickness of 2.8±0.4 nm, giving a core–shell structure with an
antiferromagnetic core, and a shell with a net magnetic moment under an applied magnetic field. The sign-reversal
of both magnetization and exchange bias field has been explained using the core-shell model. We propose that
ICNS 2013 International Conference on Neutron Scattering
these two coexisting sign-reversal phenomena can have a possible technological application in designing a
thermally assisted magnetic random access memory (TA-MRAM) element, where the storage layer bias-reversal can
be accomplished just by varying the temperature; instead of the simultaneous application of a current pulse and a
suitably directed external magnetic field.
P.203 The magnetic proximity effect in Fe3O4 core/gamma-Mn2O3 shell nanoparticles
S M Yusuf and P K Manna
Solid State Physics Division, Bhabha Atomic Research Centre, India
We have observed the phenomenon of ‘magnetic proximity effect (MPE)’ in Fe3O4 core (14.0 ± 0.2 nm) /g-Mn2O3
(1.7± 0.3 nm) shell nanoparticle system. In a heterostructure, the substrate often modifies the magnetic properties
of the deposited layers. However, a core-shell nanoparticle system, being substrate-free, rules out any such
possibility. Neutron diffraction technique has been employed by us for the investigation. Temperature dependences
of ordered site moments at tetrahedral and octahedral sites for both core and shell have been obtained from
Rietveld refinements. The ferrimagnetic nature of both core and shell has been found from our neutron diffraction
study. We have observed an enhancement of the Curie temperature (Tc) of the g-Mn2O3 shell ( 66K) compared to
its bulk value ( 40K), and the presence of magnetic ordering in its so-called paramagnetic region (i.e. above 66K)
and it extends up to room temperature. The origin of these two features has been ascribed to the proximity of the gMn2O3 shell with a high-Tc Fe3O4 core ( 858K in bulk form) and an interface exchange coupling between core and
shell. Interestingly, for the present system, we did not observe any exchange bias effect, which has been interpreted
as a signature of a weak interface exchange coupling between core and shell. The present study brings out the
importance of the relative strength of the interface coupling in governing the simultaneous occurrence of the
magnetic proximity effect and the exchange bias phenomenon in a single system. The results of the present work
are expected to generate much interest in the area of the MPE, especially in core–shell nanoparticles, which remain
unexplored so far.
P.204 The polarized neutron reflectivity study of perpendicularly CoFeB magnetic thin films
T Zhu1, V Lauter2, H Ambaye2 and J Q Xiao3
1
Institute of Physics, Chinese Academy of Sciences, China, 2Neutron Science Directorate, Oak Ridge National
Laboratory, USA, 3Department of Physics and Astronomy, University of Delaware, USA
The current-induced spin transfer torque (STT) plays an important role in spintronic devices. The magnetic tunnel
junction with a perpendicular magnetic anisotropy(PMA) enablesa small critical current density for current-induced
magnetization switching and provides a pathway for such STT devices. Here, we investigated the magnetic
properties of perpendicularly CoFeB sandwiched by MgO and Ta layers using polarized neutron reflectometry (PNR).
In principle, PNR is a technique sensitive to the compositional and in-plane magnetic depth profiles of thin films,
but not sensitive to the layer magnetization perpendicular to the sample surface. A large in-plane fieldis applied to
saturate the out-of-plane magnetization into the hard in-plane direction. Two sets of PNR data were measured: one
is under 15 Oe and another is under 10 kOe. Therefore, the analysis of layer structure and magnetic profiles can be
separated. Based on the detailed PNR results, it is found that the magnetic properties of CoFeB layers deposited
above and under MgO layer are different, which is confirmed by anomalous Hall effect measurement. Hence, PMA in
perpendicular CoFeB can not only origin from the surface anisotropy, but also be enhanced by the low
magnetization of the CoFeB layer deposited above MgO barrier.
Research was supported by NSFC and research at ORNL SNS was sponsored by BES and DOE.
ICNS 2013 International Conference on Neutron Scattering
P.205 Investigation of thin iron films using focusing neutron reflectometry
P Ziegler1, B Wiedemann1, J Stahn2, T Panzner3, U Filges3 and P Böni4
1
Technische Universität München, Germany, 2Laboratory for Neutron Scattering, Paul Scherrer Institut,
Switzerland, 3Laboratory for Developments and Methods, Paul Scherrer Institut, Switzerland, 4Physik-Department
E21, Technische Universität München, Germany
Magnetic layers and heterostructures thereof are the basic building blocks of many magneto-electronic devices such
as the read-heads of hard disk drives or magnetic random access memories (MRAMs). As Fe is one of the
technologically most important materials, we have investigated ex-situ the evolvement of the magnetism in ultrathin
Fe films on Cu(100). Due to proximity effects, the first monolayers of Fe layers grow epitaxially on Cu (fcc) assuming
an fcc structure (g-Fe). It is only for thicker iron films when the crystal structure becomes bcc. In order to improve
the signal to noise of the magnetic signal from the thin films we have used the Selene set-up [1,2] at the beam line
BOA at PSI. It is assembled from two Montel mirrors. In this set-up, the neutrons are focused by elliptically focusing
guides thus reducing the counting time of the experiment by at least one order of magnitude. In our contribution we
present reflectivity data demonstrating that polarized beam data from samples as small as 8 mm ´ 20 mm can be
accumulated within a couple of hours.
[1]
[2]
J. Stahn, J. Stahn, T. Panzner, U. Filges, C. Marcelot, and P. Böni, Nucl. Instrum. Methods A (2011) 634:
S12-S16
J. Stahn, U. Filges, T. Panzner, Eur. Phys. J. Appl. Phys. (2012) 58: 11001
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