Wednesday 10 July 2013, Starthblane & Cromdale Halls, 16:30-18:30
Poster session B – Quantum fluids, quantum magnetism and low-dimensional magnetism
P.195 Inelastic neutron scattering study of the one-dimensional spin chain cobaltate Ca3Co2O6
D T Adroja1, S Agrestini2, M Rotter3, Y Y Yuen4, M R Lees2, S Majmudar5, V Garcia Sakai1 and D M K Paul2
1
Rutherford Appleton Laboratory ISIS Facility, UK, 2University of Warwick, UK, 3Max Planck Institute for Chemical
Physics of Solids, Germany, 4Hong Kong Institute of Education, Hong Kong, 5Indian Association for the Cultivation of
Science, India
The one-dimensional cobaltate Ca3Co2O6 has attracted considerable attention recently due to its peculiar crystal
structure and very unusual magnetic properties. The crystal structure of Ca3Co2O6 consists of Co2O6 chains running
along the c-axis and they are made up of alternating face-sharing CoO6 trigonal prisms (Co3+ S=2) and CoO6
octahedra (Co3+ S=0). We have investigated Ca3Co2O6 using high energy and low energy inelastic neutron scattering
(INS) measurements. Our high energy INS study reveals two well defined strong magnetic excitations centered at 27
and 29 meV and one weak excitation at 32 meV at 5 K and 36 K. When the temperature was increased to 150 K
the 27-29 meV excitations merge into one broad peak and shift to lower energy (~20 meV at 300 K). Our low
energy INS study does not reveal any sign of magnetic scattering below 2 meV at 5 K. The absence of low energy
scattering as well as the well-defined magnetic excitations below the magnetic ordering transitions (TN1= 24 K and
TN2=12 K) indicates gapped spin waves. The presence of the broad excitations between 150-300 K has been
attributed to the crystalline electric field (CEF) splitting of the high-spin (S = 2) state of the Co3+ions at the trigonal
sites. The analysis of our INS data will be presented based on the CEF model. We will also compare the observed
INS excitations of Ca3Co2O6 with that of Ca3CoTO6 (T=Mn, Rh and Ir) compounds.
P.196 Field-induced spin-orders in 1-dimensional Co2+ chains in monoclinic CoV2O6 brannerite
A M Arevalo Lopez, M Markkula, and J P Attfield
University of Edinburgh, UK
Metamagnetism and magnetization plateaus are among the unusual properties of low dimensional magnetic oxides
based on spin-3/2 ions such as Co2+. 1/3 (of ferromagnetic) magnetization plateaus have been predicted and
observed experimentally in spin-3/2 antiferromagnetic uniform chains and are known to occur also in spin-3/2
ferromagnetic uniform chains.[1]
Temperature dependent NPD at HRPD@ISIS shows that the monoclinic brannerite-type CoV2O6 orders
antiferromagnetically at TN=15 K with a a x b x 2c supercell in which Co2+ moments of magnitude 4.77(4) mB at 4 K
lie in the ac plane and are ferromagnetically coupled within chains of edge-sharing CoO6 octahedra parallel to b.
Ferromagnetic chains are coupled antiferromagnetically to neighbouring chains in the a and c directions.[2]
Furthermore, applied magnetic field NPD from WISH@ISIS performed at H = 0, 2.5 and 5 T shows three collinear
magnetic phases as field increases: an AFM state with propagation vector (0 1 1/2), a ferrimagnetic (–1/3 1 1/3)
phase, and a (0 0 0) ferromagnetic order. In all cases, Co2+ moments of 4.4–5.0 μB have a large orbital component
and are aligned close to the c-axis direction. Spin-lattice coupling leads to a magnetostriction and volume
expansion as field increases. The ferrimagnetic phase accounts for the previously reported 1/3-magnetization
plateau, and demonstrates that monoclinic CoV2O6 behaves as an accidental triangular antiferromagnetic lattice in
which further frustrated orders may be accessible.[3]
[1]
[2]
[3]
S.A.J.Kimber, et al. Phys. Rev. B 84 (2011) 104425.
M. Markkula, et al. J. Solid State Chem. 192 (2012) 390.
M. Markkula, et al. Phys. Rev. B 86 (2012) 134401.
ICNS 2013 International Conference on Neutron Scattering
P.197 Magnetic excitation spectra in the haldane spin-chain compound SrNi2V2O8 : effect of interchain couplings
and single-ion anisotropy
A K Bera1, B Lake1, A T M N Islam1, B Klemke1, J Law2, E Faulhaber3, J Park3 and E Wheeler4
1
Helmholtz Zentrum Berlin für Materialien und Energie, Germany, 2Helmholtz Zentrum Dresden Rossendorf,
Germany, 3Technische Universität München, Germany, 4Institut Laue-Langevin, France
Spin-1 Heisenberg antiferromagnetic chains (Haldane chains) have a spin singlet ground state and gapped magnon
(S=1) excitations in contrast to the gapless spinon (S=1/2) excitations of a spin-1/2 chain[1]. Further, theoretical
phase diagram for Haldane chains in the D-J1 plane (D=single-ion anisotropy; J1=interchain J⊥/intrachain J
coupling) suggests the possibility of quantum phase transitions from the spin-liquid state to ordered states[2]. The
quasi-1D spinchain compound SrNi2V2O8 is of current interest due to the controversial reports on its position in this
phase diagram i.e., ordered [3] or spin-liquid state[4]. We report the first investigation of the magnetic excitations
in SrNi2V2O8 using single crystals.
Inelastic neutron scattering studies confirm gapped magnon excitations. Analysis of the data within a Random
Phase Approximation reveals the presence of multiple competing interchain couplings, which significantly modify
the Haldane gap and results three different gap values ( 2.4, 3.7 & 6.0 meV) at different zone centers. Single ion
anisotropy driven splitting of each mode has been found and the value is estimated to be -0.51 meV (c is the easy
axis). With the present single crystal data, the position of SrNi2V2O8 in the D-J1 phase diagram is determined to be
inside the spin-liquid state. This investigation provides insight into the effect of interchain couplings and anisotropy
on Haldane chains in general.
[1]
[2]
[3]
[4]
PRL 50, 1153.
PRB 42,4537.
PRB 62, 8921.
PRB 73, 012407.
P.198 Phonon-roton modes of liquid He beyond the roton in MCM-41
H Glyde1, S O Diallo2, R T Azuah3, M A Adams3 and O Kirichek3
1
University of Delaware, USA, 2Oak Ridge National Laboratory, USA , 3ISIS Spallation Neutron Source, Rutherford
Appleton Laboratory, UK
We present neutron scattering measurements of the phonon-roton (P-R) mode of superfluid 4He confined in MCM41 at T = 0.5 K at wave vectors, Q, beyond the roton. Measurements beyond the roton (QR = 1.92 Å-1) require
access to high wave vectors (up to Q = 4 Å-1) with excellent energy resolution and high statistical precision. Only
one previous measurement in porous media (in aerogel) with low statistical precision has been reported. At T = 0.5
K, we find that the P-R mode in MCM-41 extends out to wave-vector Q ≈ 3.6 Å-1, with the same energy and zero
width (within precision) as observed in bulk superfluid 4He. Layer modes in the roton region are also observed.
Specifically, the P-R mode energy, ωQ, increases with Q for Q > QR and reaches a plateau at a maximum energy
ωQ = 2Δ where Δ = 0.742 ± 0.01 meV is the bulk roton energy. This upper limit means the P-R mode decays to
two rotons if its energy exceeds 2Δ. It also means that the P-R mode does not decay to two layers modes. If the P-R
could decay to two layer modes, ωQ would plateau at a much lower energy, ωQ = 2ΔL where 2ΔL = 0.60 meV is
the energy of the roton like minimum of the layer mode. Rather the P-R mode and the layer modes observed in
porous media appear to be quite different modes with little interaction between them.
ICNS 2013 International Conference on Neutron Scattering
P.199 Phonon-roton modes and boson localization in disordered liquid He
H Glyde1, J Bossy2, J Ollivier3 and H Schober4
1
University of Delaware, USA, 2Institut Neel, CNRS-UJF, France, 3Institut Laue-Langevin, France, 4Institut LaueLangevin and Universite Joseph Fourier, France
We present neutron scattering measurements of the phonon-roton and layer modes of liquid helium confined in 47
Å pore diameter MCM-41 and in 25 Å pore diameter gelsil as a function of pressure and temperature. The goal is to
determine whether the well-defined phonon-roton and layer modes observed at low temperature in both bulk liquid
and in films in porous media persist as well-defined modes at higher temperatures above the superfluid phase. We
find that well defined P-R modes exist at temperatures well above the superfluid phase. This is the case in both fully
filled porous media (3D) at all pressures investigated and in films of varying thickness at saturated vapour pressure.
Liquid 4He in porous media is an example of a Bose liquid in disorder. The existence of P-R modes above Tc suggests
the existence of patches or islands of Bose-Einstein condensation (BEC) in 3D liquid (or algebraic long range order
in films), denoted localized BEC or boson localization, at temperatures above T c. The interpretation is that the welldefined P-R modes propagate in the patches of BEC. However, the patches of the BEC are separated by normal
liquid and the phases in the patches/islands are independent and not connected across the sample as required for
observable superflow. These results suggest that the present boson localization induced by temperature in 3D and
in films is the same as the boson localization observed previously at low temperature in very thin films in Vycor.
P.200 Quasiparticle breakdown and zero field splitting in the 2D quantum magnet PHCC
M Goldmann
ETH Zürich and EPFL, Switzerland
The quasi two-dimensional (2D) quantum spin liquid PHCC (piperazinium hexachlorodicuprate, (C4H12N2)Cu2Cl6) is
an excellent physical realization of a quantum spin liquid in a 2D Heisenberg antiferromagnet. The usually welldefined magnon excitations in PHCC cease to exist at certain points throughout its Brillouin zone, similar to what has
been observed in superfluid 4He. The mechanism of this breakdown, however, is not yet understood in every detail.
Making use of neutron resonant spin echo (NRSE) and direct geometry time-of-flight (TOF) neutron spectroscopy, we
are now able to determine the nature of these excitations more precisely. By NRSE experiments at the instrument
TRISP at FRM-II, we observe narrow Γ ≈ 6 μeV magnons and a finite zero field splitting (ZFS) of the single-magnon
dispersion of about 50 μeV in the low-temperature regime at the zone centre. TOF experiments at LET at ISIS confirm
this finding and, at the same time, provide an observation of the quasiparticle breakdown.
Relating the behaviour of the ZFS to the magnon disappearance, we are now able to increase our understanding of
the interactions that govern the lifetime of the excitations. This can be considered in the theoretical framework of a
lattice of dimers described by the bond-boson formalism, i.e. a hard core boson approach.
Beyond that, from a viewpoint considering instrumentation, our measurements also provide a comparison of the
resolution capabilities of these two very distinct techniques of measuring quasiparticle excitations. Our data
currently undergoes a more detailed analysis and will furthermore be supplemented by TOF data that is to be
recorded at the instrument IN5 at ILL.
ICNS 2013 International Conference on Neutron Scattering
P.201 Spin dynamics of the quasi-2d spin-1/2 heisenberg antiferromagnet on a square lattice – (5cap)2CuCl4
P Gosuly1, N Bech Christensen2, H Rønnow3, M Mourigal4, D McMorrow5 and T Perring6
1
University College London and ISIS, UK, 2Technical University of Denmark, Denmark, 3École Polytechnique Fédérale
de Lausanne, France, 4Johns Hopkins University, USA, 5University College London, UK 6ISIS Neutron Source and
University College London, UK
We report high-resolution inelastic neutron scattering studies on the quasi-2D spin-1/2 quantum Heisenberg
antiferromagnet on a square lattice (QHAFSL) [1] subjected to an applied magnetic field. (5CAP)2CuCl4 (CAPCC) is
an excellent realization of the quasi-2D spin-1/2 QHAFSL. It is a metal-organic compound with moderate exchange
(J ≈ 0.10 meV, Hsat = 3.62 T) and low ordering temperature (TN=754 mK) [2], properties that make it suitable for
experimental studies over its whole phase diagram. When subjected to an applied magnetic field, the 2D QHAFSL is
predicted to have interesting dynamics. Theory predicts a field region close to Hsat where one-magnon states mix
with two-magnon continuum and lead to instability of the former through a process called field-assisted magnon
decay [3,4]. Recent theoretical work suggests that such a magnon instability survives in the quasi-2D case [5]. We
will present spin-wave data measured on the LET spectrometer at ISIS at H=7 T > Hsat that show that CAPCC is welldescribed by a Hamiltonian with nearest-neighbour in-plane exchange J ≈ 0.10 meV and inter-plane coupling Jc ≈
0.20 × J. Knowledge of the values of the exchange constants in the 2D QHAFSL is essential because it is the starting
point for theoretical investigations. Further, we will present results at H=0.925 × H sat for the spin dynamics and
damping, in the region where field-assisted magnon decay is predicted.
[1]
[2]
[3]
[4]
[5]
E. Manousakis et al. Rev. Mod. Phys. 63, 1 (1991)
F.C. Coomer et al. Phys. Rev. B 75, 094424 (2007)
M.E. Zhitomirsky et al. Phys. Rev. Lett. 82, 4536 (1999)
M.E. Zhitomirsky et al. Rev. Mod. Phys. 85, 219-243 (2013)
W. T. Fuhrman et al. Phys. Rev. B 85, 184405 (2012)
P.202 Larmor labeling methods: neutron resonance spin echo spectroscopy beyond standard line width
measurements
F Groitl1, K Rolfs1, D Quintero-Castro1, K Kiefer1, T Keller2and K Habicht1
1
Helmholtz-Zentrum Berlin, Germany 2Max-Planck Institut for Solid State Research, Germany
Exploring new territory for Neutron Resonance Spin Echo (NRSE) spectroscopy beyond measuring lifetimes of
elementary excitations we present two experiments which benefit from the high resolution offered by the NRSE
method. The first experiment aims at separating a mode doublet with an energy split which is difficult to resolve with
standard neutron scattering techniques. For modeling the resulting spin echo signal t is essential to take violation of
the spin echo conditions and arbitrary local gradients of the dispersion surface into account which we provide by a
major generalization of a model for the NRSE resolution function for life time measurements. Investigating this
model we present experimental results obtained using a unique tunable double dispersion setup. The results
demonstrate the necessity to consider the generalized model for data analysis. The second class of experiments is
dedicated to line shape analysis of temperature dependent asymmetric line broadening. Measurements were
performed on Cu(NO3)2×2,5D2O, a model material for a 1-D bond alternating Heisenberg chain, and on Sr3Cr2O8, a
dimerized spin-1/2 antiferromagnet. For the first time this effect was measured with high-resolution NRSE. The
particular advantage of the NRSE method is its direct access to the line shape in the time domain since there is no
convolution of the signal with the resolution function of the spectrometer. This is an important advantage compared
to other high resolution neutron scattering techniques, e.g. time-of-flight. As an important fact it could be shown
that for a line shape differing from Lorentzian shape, the phase of the spin echo signal becomes a non-linear
function of the spin echo time τ.
ICNS 2013 International Conference on Neutron Scattering
P.203 Experimental confirmation of spin gap in spin-3/2 substances RCrGeO5 (R = Y, Nd or 154Sm)
M Hase1, M Soda2, T Masuda2, D Kawana3, T Yokoo3 and S Itoh3
1
National Institute for Materials Science (NIMS), Japan, 2University of Tokyo, Japan, 3High Energy Accelerator
Research Organization (KEK), Japan
One interesting phenomenon in quantum spin systems is the appearance of spin-singlet ground states with a spin
gap (singlet-triplet excitation). When the spin value is larger than 1, spin-singlet ground states with a spin gap have
not been proved experimentally. We can expect spin-3/2 antiferromagnetic (AF) alternating chains of Cr3+ in
RCrGeO5 (R = Y or rare earth) and spin-singlet ground states with a spin gap. We performed inelastic neutron
scattering (INS) experiments on RCrGeO5 (R = Y, Nd or 154Sm) powders and confirmed the spin gap excitations. We
used the High Resolution Chopper (HRC) spectrometer at the BL12 at J-PARC.In YCrGeO5, excitations are apparent
between 5 and 25 meV at 4 K.Intensities of the excitations are strong in the small Q range. We also measured INS
spectra at 200 K and observed decrease of the intensities. Probably, most of excitations are magnetic. We
calculated the intensity map in the energy–Q1D planeusing the Tomiyasu method. The results correspond to results
of a single crystal measured along the spin chain direction (Q1D). The intensity is the strongest around Q1D = 0.5 (p)
as expected in AF spin chains. The spin gap value is evaluated as 8 meV. The dispersion is apparent below Q1D = 1.
In NdCrGeO5 and SmCrGeO5, broad excitations are apparent between 18 and 25 meV at 4 K and between 10 and
40 meV at 7.8 K, respectively. We consider that most of excitations are magnetic from Q and T dependence of the
excitations.
P.204 Search for cholesteric spin order in LiCuVO4
E Hirtenlechner1, M Enderle1, M Mourigal2, B Fåk3, A Prokofiev4 and R K Kremer5
1
Institut Laue Langevin, France 2Johns Hopkins University, USA 3Commissariat à l’Energie Atomique, INAC, SPSMS,
France, 4Institute for Solid State Physics, TU Wien, Austria 5Max Planck Institute for Solid State Research, Germany
For certain spiral magnets a chiral spin-nematic or spin-cholesteric phase should exist just above the phase
transition. It is characterized by a long-range ordered chirality and absence of dipolar long-range order [1].
LiCuVO4 develops a second order phase transition into a cycloid magnetic structure and simultaneously a
ferroelectric polarization below TN = 2.4 K. The ferroelectricity has been shown to be driven by the one-dimensional
frustrated nearest and next-nearest neighbor interactions, while anisotropic interactions of Dzyaloshinskii-Moriya
type are absent [2]. A low spin-flop transition in magnetic fields applied within the cycloid plane indicates a small
exchange anisotropy of XY type [2]. LiCuVO4 thus appears ideally suited for a search of this cholesteric phase.
We present a polarized neutron scattering study with an applied electric field and zero magnetic field of the purely
elastic scattering and the onset of the magnetic order across the phase transition.
[1]
[2]
S. Onoda and N.Nagaosa, Phys. Rev. Lett. 99, 027206 (2007).
M. Mourigal et al., Phys. Rev. B 83, 100409(R) (2011).
ICNS 2013 International Conference on Neutron Scattering
P.205 Effect of magnetic bond disorder on spin dynamics and on field induced ordering transition in a quantum
spin liquid
D Hüvonen, S Gvasaliya and A Zheludev
ETH Zürich, Switzerland
We study the effect of magnetic bond disorder in a gapped (Eg = 1meV) spin-1/2 quantum spin liquid PHCC,
(C4H12N2)Cu2(Cl1-xBrx)6. Magnetic bond disorder is induced by chemical substitution. The unperturbed compound is a
well studied example of the field induced magnon Bose-Einstein condensate. Bond disorder (x=0.005..0.1) affects
both, the gapped and condensate phases, as seen from high field bulk and neutron measurements. Neutron
diffraction reveals that in disordered samples the high field order peak stays resolution limited, but develops history
dependence. However, the order parameter critical exponent shows no deviation from the unperturbed system [1].
Using triple axis and time-of-flight neutron spectroscopy we find that bond disorder increases the spin gap, reduces
the magnon bandwidth and shortens the lifetimes. A spin wave model of the clean system with renormalized
parameters provides adequate description of the spectra in disordered samples. RPA treatment of the model
coincides with the measured gap hardening at higher temperatures. Resolution convoluted analysis of magnon
spectrum unveils that the intrinsic linewidths are wavevector dependent with the damping increasing by about a
factor of three at the zone boundaries [2]. The effect can be correlated with single-magnon density of states function
which implies magnon-impurity scattering as the leading damping mechanism.
[1]
[2]
D. Huvonen et al. PRB 85, 100410(R) (2012).
D. Huvonen et al. PRB 86, 214408 (2012).
P.206 Quantum criticality in the quasi-1D Ising antiferromagnet CoCl2•2D2O in transverse field
N B Christensen1, J Larsen1, K Lefmann2, R Toft-Petersen3, G Ehlers4, T K Schäffer2, A Baden2, S Adsersen2, S L
Holm2 and M Sales5
1
Technical University of Denmark, Denmark, 2University of Copenhagen, Denmark, 3Helmholtz-Zentrum Berlin für
Materialien und Energie GmbH, Germany, 4Oak Ridge National Laboratory, USA, 5University of Copenhagen,
Denmark and Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
As experimental realizations of model spin Hamiltonians, for which theory predicts quantum criticality have emerged
from the chemistry laboratories, recent years have seen an increasing interest in neutron scattering studies of
quantum phase transitions [1-3]. The simplest example of Ising spins in a transverse magnetic field has been
studied experimentally in a 3-dimensional setting in LiHoF4 [2] and for weakly coupled chains in CoNb2O6 [3-4]. We
have studied CoCl2.2D2O which, approximating an effective S=1/2 model with Ising-like exchange interactions
[5,6]. Compared to CoNb2O6 [3-4], interchain interactions are stronger relative to the dominant intrachain
interaction, so 3-dimensional effect are expected to be more prominent. Our studies focus on the degree of
similarity between the excitation spectra of CoNb2O6 and CoCl2.2D2O and on the effects of the different ratios of
inter-chain to intra-chain couplings. We present inelastic neutron scattering data taken for fields in the vicinity of the
quantum critical field Hc=16T separating the ordered antiferromagnetic and polarized paramagnetic states, and
show how the excitation spectrum gap closes at Hc and re-emerges at higher fields.
[1]
[2]
[3]
[4]
[5]
[6]
C. Rüegg et al, nature 423, 62 (2003)
H. M. Rønnow et al, science 308, 389 (2005)
R. Coldea et. al., science 327, 177 (2010)
H. Mollymoto et. al., JPSJ 49, 108 (1980)
W. Montfrooij et. al., PRB 64, 134426 (2001)
S. Lee et. al., nature physics 6, 702 (2010)
ICNS 2013 International Conference on Neutron Scattering
P.207 Density– and spin–density fluctuations in liquid 3He: comparison of theory and experiments
T Lichtenegger1, E Krotscheck1, R Holler1, B Fåk2 and H Godfrin3
1
Johannes Kepler University, Austria, 2SPSMS, UMR-E CEA/UJF France, 3CNRS-Institut Néel, France
Progress on the microscopic understanding of density fluctuations in liquid 3He at T = 0K has been made
recently, employing a variational approach in terms of single– and double–pair fluctuations from the correlated
ground state to find the dynamic structure function of the system.1 We extend the same
manifestly microscopic techniques to the description of spin–density waves in 3D liquid 3He and find good
agreement with experiments.2 Our calculations show that this excitation branch is a macroscopic manifestation of
exchange effects. As in the density channel the inclusion of pair fluctuations, i.e. intermediate states that cannot
be described by the quantum numbers of a single particle, is essential for a quantitative description of the
physics. These lead to explicit expressions for both an energy dependent renormalization of the exchange
interaction and self-energy corrections to the single-particle spectrum, which in turn are needed to obtain
quantitative results in the density channel.
[1]
[2]
Böhm et al. (2010). “Dynamic many-body theory: Dynamics of strongly correlated Fermi fluids”.
Phys. Rev. B 82, 224505.
Fåk et al. (1998). “Temperature dependence of spin–density fluctuations in liquid 3He”. J. Low
Temp. Phys. 110, 417-424.
P.208 The Quasi-One-Dimensional Metallic Antiferromagnet NaV2O4 Studied by Neutrons, Muons and Photons
M Mansson1, H Nozaki2, J Sugiyama2, Y Ikedo3, V Pomjakushin4, Y Sassa5, O Tjernberg6, J H Brewer7, T Goko8, B
Roessli4, K H Chow9, M Harada2, V Sikolenko10, A Cervellino4, E J Ansaldo11 and H Sakurai12
1
EPF Lausanne, Switzerland, 2Toyota Central Research and Development Laboratories (TCRDL), Japan, 3Institute of
Materials Structure Science, Japan, 4Paul Scherrer Institut, Switzerland, 5ETH Zürich, Switzerland, 6Royal Institute of
Technology KTH, Sweden, 7University of British Columbia, Canada, 8Columbia University, USA, 9University of Alberta,
Canada, 10Karlsruhe Institute of Technology, Germany, 11TRIUMF, Canada, 12National Institute for Materials Science
(NIMS), Japan
The microscopic magnetic nature of NaV2O4, in which the V ions form quasi-1D (Q1D) zigzag chains along the b-axis,
was investigated by positive muon-spin spectroscopy (μ+SR) [1]. Powder samples were studied down to T = 1.8 K
and a static antiferromagnetic order appears below TN= 140 K. In order to clarify the reason for the coexistence of
long-range AF order and metallic conductivity in NaV2O4, neutron powder diffraction experiments were performed.
The analysis of the magnetic Bragg peaks below TN= 140 K demonstrated the formation of an incommensurate spin
density wave order (IC-SDW) [2] with k = (0, 0.191, 0); the ordered moment was estimated to be (0, 0, 0.77μB) at
T = 20 K. Further, from synchrotron radiation x-ray diffraction, we found no indication of structural phase
transitions. Hence, the IC-SDW order is thought to be caused by an intrinsic instability of the V 2O4 zigzag chain
system at low T. Recently, we found details in our μ+SR data, indicating the presence of a helical magnetic order in
this compound [3], which was further supported, by NMR and bulk measurements [4]. Finally, the electronic
structure of single crystal NaV2O4 was investigated using angle-resolved photoelectron spectroscopy (ARPES). The
spectra show two dispersing bands crossing the Fermi level and a 1D Fermi surface strongly nested along the b-axis
[5]. The nesting vector is found as k = [0, 0.195, 0], perfectly matching our neutron diffraction data.
[1]
[2]
[3]
[4]
[5]
J. Sugiyama et al. Phys. Rev. B 78, 224406 (2008)
H. Nozaki et al. Phys. Rev. B 81, 100410(R) (2010)
O. Ofer et al. Phys. Rev. B 82, 094410 (2010)
H. Takeda et al. Phys. Rev. B 86, 174405 (2012)
M. Månsson et al. publication in progress
ICNS 2013 International Conference on Neutron Scattering
P.209 Impurity scattering and magnon damping in a prototypical 2D-XY antiferromagnet
N Martin1 and L-P Regnault2
1
Forschungsneutronenquelle Heinz Maier-Leibnitz - FRM II, Germany, 2CEA Grenoble INAC-SPSMS-MDN, France
Two-dimensional magnetic systems, as well as their 1D counterpart, have been extensively studied experimentally
since the introduction of neutron scattering. Such an interest is essentially motivated by the apparently easy
theoretical comprehension of their dynamic properties. BaNi2(PO4)2 is a very good prototype of 2D XY
antiferromagnet which orders in a collinear structure described by a propagation vector k = (0,0,0) under a Néel
temperature of 23.5 K [1]. Recently, we have undertaken high resolution resonant spin echo (NRSE) studies, aiming
at measuring the lifetime of magnons emerging from its ordered state, with a sub- 10 μeV resolution. The excitation
spectrum displays two branches, corresponding respectively to in- and out-of-plane spin fluctuations. The latter is
gapped with an energy of about 2.8 meV and sees its lifetime limited by scattering on impurities, in accordance with
recent damping calculations [2]. Studying the acoustic branch has proven to be more difficult, mainly because of
resolution effects. This investigation is therefore a good occasion to stress on the limitations of the otherwise
powerful NRSE technique.
[1]
[2]
L.-P. Regnault and J. Rossat-Mignod, in Magnetic Properties of Layered Transition Metal Compounds, Ed.
L.J. De Jongh (Kluwer Academic, 1990) p. 271.
A.L. Chernyshev, M.E. Zhitomirsky, N. Martin and L.-P. Regnault, Phys. Rev. Lett. 109, 097201 (2012)
P.210 Magnetic structure and excitations of the one-dimensional quantum antiferromagnet RbCoCl3
M Mena1, E Hirtenlechner2, N Hänni3, S Ward4, K W Krämer3, C Rüegg4 and D F McMorrow
1
University College London, UK, 2ILL, France 3University of Bern, Switzerland 4PSI, Switzerland
RbCoCl3 is a hexagonal perovskite in which the cobalt atoms have effective ½ spins and form linear chains along
the c-axis. We present the results of neutron diffraction and inelastic neutron scattering experiments on this
compound. Our work reveals two magnetic phase transitions: the antiferromagnetic ordering at TN= 28K and a
second phase transition at TC= 14K. It also shows the existence of a SW spectrum between TC and TNand above TN,
as well as a splitting of the SW in two modes below TC. We describe the system and its magnetic excitations using a
quasi 1D Ising-like spin model [1] [2] with weak inter-chain coupling, which is a case of strongly anisotropic
Heisenberg Hamiltonian [3]. The lowest-lying excited magnetic mode in its spectrum consists of domain-wall spin
waves (SW). The results and analysis are discussed also in relationship to previous experiments on isostructural
CsCoCl3 and TlCoCl3.
[1]
[2]
[3]
J. P. Goff, D. A. Tennan and S. E. Nagler, Phys.Rev. B 52, 15992(9) (1995).
A. Oosawa, Y. Nishiwaki, T. Kato and K. Kakurai, J. Phys. Soc. Jpn. 75, 15002 (2006).
N. Ishimura and H. Shiba, Progr. Theor. Phys. 63, 743 (1980)
P.211 Low temperature dynamics of magnons in a spin-1/2 ladder compound
B Nafradi1, T Keller2, H Manaka3, U Stuhr4, A Zheludev5and B Keimer2
1
EPFL/IPMC, Switzerland 2Max-Planck-Institute, Germany 3Kagoshima University, Japan, 4Paul Scherrer Institute,
Switzerland, 5Neutron Scattering and Magnetism Group, Switzerland
We have used a combination of neutron resonant spin-echo and triple-axis spectroscopies to determine the intrinsic
fine structure, linewidth, and energy, of the magnon resonance in the model spin-1/2 ladder antiferromagnet IPACuCl3 at temperatures T<Δ0/kB. Calculations based on the non-linear sigma model with isotropic 1D exchange
interactions yield a surprisingly good description of the data at high temperatures. At temperatures T<<Δ0/kB,
however, where magnons are expected to be good quasiparticles, we have found that spin-space and real-space
ICNS 2013 International Conference on Neutron Scattering
anisotropies in the spin Hamiltonian as well as scattering of magnons from a dilute density of impurities induce
substantial deviations from the predictions of this model. These effects are generic to all experimental realizations of
1D model Hamiltonians and should therefore be taken into account in order to obtain quantitative descriptions of
experimental data.
By Br substitution we also find, that bond defects induce a blueshift, δΔ, and broadening, δΓ, of the magnon gap
excitation compared to the pure compound. At temperatures exceeding the energy scale of the inter-ladder
exchange interactions, δΔ and δΓ are temperature independent within the experimental error, in agreement with
Matthiessen's rule according to which magnon-defect scattering yields a temperature independent contribution to
the magnon mean free path. Upon cooling, δΔ and δΓ become temperature dependent and saturate at values
lower than those observed at higher temperature, consistent with the crossover from one-dimensional to twodimensional spin correlations with decreasing temperature observed in pure IPA-CuCl3.
P.212 Charge density wave induced by ir site-selective lattice distortions in 9r-BaIro3
H J Noh1, J Jeong1, B Chang1, S Lee2 and H D Kim3
1
Chonnam National University, Korea, 2Korea Atomic Energy Research Institute, Korea, 3Pohang University of
Science and Technology, Korea
We present evidence for the charge density wave (CDW) mechanism of quasi-one-dimensional 9R-BaIrO3. The CDW
phase of the compound was reported a decade ago, but its exact mechanism has not been clearly revealed for a
long time. We resolved this issue by performing the temperature dependent neutron diffraction (ND), x-ray
diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). Our ND/XRD studies uncovered that the cell
parameters show an unconventional thermal expansion behavior that is strongly correlated with the CDW phase
transition. The detailed structure analysis revealed that the distortion of the IrO6 octahedra is Ir site-selective in
crystallography, inducing the CDW phase via an Ir 5d level shift below TC=175 K. In addition, the Ir charge
disproportionation due to the energy level shift was confirmed in the Ir 4f core-level XPS spectra.
P.213 Structural complexity of Pr2NiO4+δ during electrochemical oxygen intercalation studied by in situ neutron
and synchrotron diffraction
W Paulus1, M Ceretti1, O Wahyudi1, A Villesuzanne2, J M Bassat2, G André3, A Cousson3, A Bosak4, D Chernychov4, J
Schefer5 and W Paulus1
1
University Montpellier 2, France, 2ICMCB Bordeaux, France, 3LLB Saclay, France 4ESRF, 5PSI Villigen, Switzerland
Pr2NiO4+δ belongs to the few known non-stoichiometric oxides of the K2NiF4 family with high oxygen ion mobility
already at ambient temperature and figuring among the most promising candidates for oxygen membranes in solid
oxide fuel cells (SOFC) [1]. Pr2NiO4+δ can accommodate a huge amount of extra oxygen atoms on interstitial sites,
the non-stoichiometric region being 0 < δ < 0.26 .
We investigated by in situ neutron powder diffractionthe structural changes as a function of the oxygen
stoichiometryof Pr2NiO4+δat ambient temperature in a specially designed electrochemical cell. Extremely complex
structures with oxygen ordering on a length scale of more than 200 Å have been evidenced, combining NPD and
single crystal synchrotron diffraction as a function of the charge transfer. The giant long-range structural
correlations, implying unit cell volumes of more than 3.000.000Å3, are discussed to form soft phonon modes
allowing phonon assisted oxygen diffusion in solid oxides at already ambient temperature [2-4].
[1]
[2]
E. Boehm, J.M. Bassat, P. Dordor, F. Mauvy, J .C Grenier, P. Stevens, Solid States Ionics 176 (2005) 27172725
A. Villesuzanne, W. Paulus, A. Cousson , S. Hosoya, L. Le Dréau , O. Hernandez, C. Prestipino M. Ikbel
Houchati, J. Schefer, J Solid State Electrochem, Volume: 15 Issue: 2 Pages: 357-366 (2011)
ICNS 2013 International Conference on Neutron Scattering
[3]
[4]
L. LeDreau, C. Prestipino, O. Hernandez, J. Schefer, G.Vaughan, S. Paofai, J. Manuel Perez-Mato, S.
Hosoya, and W. Paulus, Inorganic Chemistry 2012, 51, 9789-9798
M. Ikbel Houchati, M. Ceretti, C. Ritter and W. Paulus,Chem. Mater. 2012, 24, 3811-3815
P.214 Incommensurate dynamic correlations and continuum scattering in the quantum-disordered BiCu2PO6
K Plumb1, Z Yamani2, M Matsuda3, A Savici3, G Granroth3, G J Shu4, F C Chou4 and Y-J Kim1
1
University of Toronto, Canada, 2National Research Council of Canada, Canada, 3Oak Ridge National Laboratory,
USA, 4National Taiwan University, Taiwan
The canonical spin-1/2 two-leg-ladder consists of pairs of spin half chains coupled via a short-range Heisenberg
"rung" exchange interaction. The rung coupling confines pairs of elementary spinon excitations and the dynamic
structure factor is dominated by a well-defined single particle peak. Additional further neighbour antiferromagentic
couplings along the chains may introduce frustration leading to very rich physical phenomena and a dramatically
altered magnetic excitation spectrum. Here, we report comprehensive inelastic neutron scattering measurements on
single crystals of the frustrated two-leg ladder BiCu2PO6, whose ground state is described as a spin liquid phase
with no static magnetic correlations down to 5 K. A combination of thermal triple-axis and time-of-flight
experiments were performed to explore magnetic excitations over a broad range of phase space. Operation of the
instruments in a high resolution configuration enabled a detailed measurement of the entire dynamical structure
factor over many Brillouin zones. Our measurements reveal an extremely rich, and highly unusual, magnetic
excitation spectrum in BiCu2PO6. Two branches of steeply dispersing long-lived spin excitations are observed with
gaps of 1.90(9) meV and 3.95(8) meV. Significant frustrating next-nearest-neighbor interactions along the ladderleg drive the minimum of each excitation branch to incommensurate wavevectors 0.574 and 0.553 for the lower
and upper energy branches respectively. Intriguingly, the spin excitations merge into a broad continuum near the
top of each excitation band which persists to an upper boundary of 40 meV.
P.215 The complex magnetic phase diagram of the quantum spin chain material, Linarite, PbCuSO 4(OH)2
K Rule1, B Willenberg2, M Schaepers3, M Reehuis2, B Ouladdiaf4, A Wolter-Giraud3 and S Suellow5
1
ANSTO - Bragg Institute, Australia, 2Helmholtz Zentrum Berlin for Materials and Energy, Germany, 3Leibniz Institute
for Solid State and Materials Research IFW Dresden, Germany, 4Institute Laue Langevin, France, 5Institute for
Condensed Matter Physics, Germany
One of the simplest models exhibiting 1D frustrated quantum interactions is the J1-J2 model where competing
ferromagnetic (FM) nearest-neighbour (NN) interactions (J1>0) and antiferromagnetic (AFM) next-nearestneighbours (NNN) (J2<0) can give rise to novel phenomena such as multiferroicity for spiral spin states or dimerized,
Luttinger liquid phases [1]. Linarite, PbCuSO4(OH)2 is a natural mineral ideally suited to the study of frustration in
J1-J2 systems due to an accessible saturation field and the availability of large single crystals well suited to neutron
investigations. In this material the Cu2+ ions form spin S = ½ chains along the b direction with dominant NN FM
interactions and a weaker NNN AFM coupling, resulting in a magnetically frustrated topology [2].
We present a neutron diffraction study of linarite revealing a helical magnetic ground state structure with an
incommensurate propagation vector of (0 0.186 ½) below TN = 2.8K in zero magnetic field [3]. Thermodynamic
data coupled with neutron diffraction in fields up to 10 T (B b) reveal a very rich magnetic phase diagram. Our data
establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic NN and
antiferromagnetic NNN interactions.
[1]
[2]
[2]
S. Furukawa et al., Phys Rev Lett 105 257205 (2010)
A.U.B. Wolter et al., Phys Rev B 84 184419 (2011)
B. Willenberg et al., Phys Rev Lett 108, 117202 (2012)
ICNS 2013 International Conference on Neutron Scattering
P.216 Impurity physics, long range order and excitations in the frustrated quantum spin ladder BiCu2(1x)Zn(2x)PO6 studied by neutron scattering
M Skoulatos1, P Merchant2, S Ward3, O Zaharko1, C Niedermayer1, E Faulhaber4, S Wang5, K Conder1, M
Kenzelmann1 and C Rueegg6
1
Paul Scherrer Institut, Switzerland, 2University College London, UK, 3University College London, UK, / Paul Scherrer
Institute, Switzerland, 4FRM-II, Germany, 5Paul Scherrer Institute,Switzerland / EPF Lausanne, Switzerland 6Paul
Scherrer Institute, Switzerland / University of Geneva, Switzerland
Neutron scattering is used to directly determine the ground state and the spin dynamics in single-crystal samples of
the Zn impurity-doped quantum spin ladder BiCu2(1-x)Zn(2x)PO6 [1,2]. Singlets on ladder rungs are broken and a
free moment appears alongside every Zn impurity. Long range order is found at incommensurate wave vectors,
weakly dependent upon Zn concentration. The data are best modeled by an amplitude modulated spin structure.
External magnetic field is applied along all principal directions and the H-T phase diagram is explored. Correlation
lengths are measured and compared to existing theory. Furthermore, Zn-induced sub-gap excitations were found,
showing a breakdown of the singlet-triplet gap as a function of increasing Zn concentration.
[1]
[2]
Y. Kohama, S. Wang, A. Uchida, K. Prsa, S. Zvyagin, Y. Skourski, R.D. McDonald, L. Balicas, H. Ronnow, Ch.
Rueegg and M. Jaime, Phys. Rev. Lett. 106, 167204 (2012).
F. Casola, T. Shiroka, A. Feiguin, S. Wang, M. S. Grbic, M. Horvatic, S. Kraemer, S. Mukhopadhyay, C.
Berthier, H.-R. Ott, H.M. Ronnow, Ch. Rueegg, and J. Mesot, arXiv:1211.5522 [cond-mat.str-el].
P.217 Thermal effects in quantum magnets
A Tennant1, B Lake1, M Telling2 and F Essler3
1
Helmholtz Center Berlin, Germany 2ISIS Facility, Rutherford Appleton Laboratory, UK 3 Oxford University, UK
Neutron scattering is important to understanding the nature of the ground states and excitations in quantum
magnets. Now the effects of temperature on the correlation functions are of increasing interest and importance
because of their relation to transport properties and quantum decoherence of states. To investigate this we have
undertaken extensive measurements of the correlation functions in a model magnet copper nitrate. This system is
an alternating chain which is equivalent to a hard core boson system in 1D. By exploiting the use of a magnetic field
to change the boson density we investigate the relationship of the scattering to that of an out of equilibrium excited
state. The measurements and theory show a close relationship to the problem of particle injection into a strongly
correlated state.
P.218 Excitations in bond disordered spin ladder systems
S Ward1, K Krämer2, M Boehm3, D Lee4, D Mcmorrow5, C Rüegg1
1
Paul Scherrer Institut, Switzerland, 2University of Bern, Switzerland, 3Institut Laue-Langevin, France, 4Helmholtz
Zentrum Berlin, Germany, 5University College London, UK
Studies of one dimensional spin systems are fundamental to our understanding of magnetism. One such
dimensionally constrained geometry is the spin ladder, which has been theoretically and experimentally studied in
recent years. (C5H12N)2CuBr4 is one such system which exhibits this spin geometry. It is well characterised with a
fully accessible phase diagram and is considered possibly the most prototypical spin ladder model material.
Alterations to the pure spin ladder geometry include the fascinating case of bond disorder, which can lead to
localisation, Griffihs phases and the elusive Bose Glass phase. By substituting Cl for Br it is possible to create new
bond disordered compounds [1]. In these the superexchange interactions transition from those of the pure Br case
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to the Cl case with typically lower exchange energies. Determination of the exchange interactions for both pure
cases will be provided from inelastic neutron scattering (INS). Neutron powder diffraction confirms that the series is
isostructural to both pure cases. The effect of bond disorder in these materials has been investigated by magnetic
susceptibility measurements and the average exchanges determined. INS is used to examine the excitation spectra
in these disordered systems. The measured spectrum is non-trivial as both multiple dispersive and non-dispersive
modes coexist. The results will be discussed in the context of several theoretical predictions for bond disordered
systems.
[1]
S. Ward etal. J. Cond. Matt. 25, 014004 (2013)
P.219 Magnetic behavior and crystal structure of one-dimensional quantum spin system Li2ZrCuO4
Y Yasui1, N Igawa2, K Kakurai2, A Hoshikawa3 and T Ishigaki3
1
Meiji University, Japan, 2Japan Atomic Energy Agency, Japan, 3Ibaraki University, Japan
Magnetic properties and crystal structure have been studied for quasi one-dimensional spin 1/2 system Li2ZrCuO4
with CuO2 ribbon chains which are formed of edge-sharing CuO4 square planes. Due to the geometrical
characteristic of the crystal structure of CuO2 ribbon chains, the nearest-neighbor exchange interaction J1 between
spins is ferromagnetic, and the second neighbor interaction J2 is antiferromagnetic. Under these situations, if the
spin system exhibits the magnetic transition, the system has often helical magnetic structure, and is often
accompanied with ferroelectricity called multiferroic. We have found that LiVCuO4 and PbCuSO4(OH)2 with the CuO2
ribbon chains have the helical magnetic structure and multiferroic behavior [1,2]. On the other hand, Li 2ZrCuO4 is
not accompanied with ferroelectricity at magnetic transition temperature [3]. Here, the powder neutron diffraction
measurements have been carried out for Li2ZrCuO4 using the neutron diffraction device (iMATERIA) installed at MLF
in J-PARC and the high resolution powder diffractometer (HRPD) installed at JRR-3 in Tokai. The analyzed results of
the magnetic structure and detailed crystal structure of Li2ZrCuO4 are presented. On the bases of the obtained data,
reasons of no appearance of ferroelectricity are discussed.
[1]
[2]
[3]
Y. Naito et al.: J. Phys. Soc. Jpn. 76 (2007) 023708.
Y. Yasui et al.: J. Phys. Soc. Jpn. 80 (2011) 033707.
Y. Tarui et al.: J. Phys. Soc. Jpn. 77 (2008) 043703.
P.220 Spin and hole dynamics in carrier doped quantum haldane chain
T Yokoo1, S Itoh1, D Kawana1 and J Akimitsu2
1
High Energy Accelerator Research Organization (KEK) 2Aoyama-Gakuin University, Japan
Spins in one-dimensional (1D) chains show unusual properties such as Haldane state and spin-Peierls, by strong
quantum nature. In particular, spin singlet is the basic starting point as a ground state of the quantum spin state.
Another interest in quantum spin systems is the cooperation between charges and spins. Practically it is hard to
realize the carrier doping in 1D material because the localization of carriers occur in low temperature. We present
spin and hole dynamical properties in Nd2-xCaxBaNiO5, which is successfully hole doped 1D Haldane system. The
lightly doped x=0.035 carrier content were measured by means of pulsed neutron inelastic scattering. It is clearly
observed the entire one-magnon band with spin gap (Haldane gap) at magnetic zone center. The energy at zone
boundary reaches 60 meV that is less comparing to undoped Haldane chain. On the other hand, the gap slightly
increases in its energy. Also, the structures within the gap were observed. This is possibly originated by the
dynamics of doped-hole.
ICNS 2013 International Conference on Neutron Scattering