Tuesday 9 July 2013, Strathblane & Cromdale Halls, 16:30-18:30
Poster session A - Magnetic oxides
P.086 Magnetic structure of TbMn2-xFexO5 for x=0.30
N Aliouane1, A Malyuk2, S Landsgesell3 and D Argyriou4
1
Paul Scherrer Institute, Laboratory for Neutron Scattering, Switzerland, 2Leibniz Institute for Solid state and
Materials Research, Germany, 3Helmoltz Zentrum, Germany, 4European Spallation Source ESS AB, Sweden
Manganite compounds present a large range of functional properties from colossal magnetoresitor to multiferroic
properties. TbMn2O5 is well known materials that exhibit complex magnetic phase transitions and multifunctional
properties[1]. All the magnetic properties in this system is controlled by frustrations. Magneto-striction is at the
origin of the ferroelectric properties below 25K. These frustrations are usually tuned by chemical
substitution/doping. Fe doped materials (TbMn2-xFexO5) in ceramics sample have shown enhancement of Ps [2]. The
frustration have been tuned by inserting Fe3+ (HS, S=5/2) for Mn3+ without distorting the structure at room
temperature. Large single crystals of TbMn2-xFexO5 (with x 0.30) have been grown by flux method and characterized
by magnetic susceptibility measurements, dielectric spectroscopy and single crystal neutron diffraction on 4 circles
diffractometer TriCs at SINQ PSI, (Switzerland) facility to probe nuclear and magnetic properties in relationship with
its multiferroic properties. Susceptibility measurements indicate that TbMn2-xFexO5 with x=0.3 have similar
anomalies and anisotropy as x=0 but higher temperatures. At Tc1 25K, it undergoes to ferroelectric transition
where a spontaneous electrical polarization (Ps) occurs along the b direction. The Ps is induced by the Mn long
range commensurate anti-ferromagnetic ordering. An additional transition is observed at T 180K which is linked
with a structural transition. Magnetic structure of Mn and Tb have been determined at 40, 25 and 5K respectively
and presented in this work and discuss in the light of its physical properties.
[1]
[2]
N. Hur et al., Nature 429, 392 (2004)
S.Kobayashi et al., J Phys Soc Jpn 73, 3439 (2007)
P.087 Charge, spin, vacancy and cation ordering in Sr(Cr1-xFex)O3-d (x = 0, 0.5) perovskite superstructures - new
hard-soft phases and substituted derivatives
A M Arevalo Lopez1, J A Rodgers2, M S Seen2, F Sher3 and J P Attfield1
1
CSEC & School of Chemistry, University of Edinburgh, UK, 2University of Edinburgh, UK, 3Lahore University of
Management Sciences, Pakistan
Low temperature reduction of the high pressure perovskite SrCrO3 (hard-soft chemistry) allows us to obtain two new
SrCrO3-δ phases (δ=0.2 and 0.25) with unusual superstructures and properties.[1] Both are re-oxidized to cubic
SrCrO3 on standing air and form long-period Cr3+/Cr4+ charge-density waves. Reconstruction from octahedral
geometry to tetrahedral environments in widely spaced (111) planes gives 15R and 6H repeat sequences for δ=0.2
and 0.25 respectively. D20@ILL data reveal a long range spin order in the 15R phase where ferromagnetic layers
are antiferromagnetically coupled to adjacent spin planes along c. Magnetic moments are parallel to the c-axis with
refined magnitudes of 2.4(5), 1.3(3) and 1.1(2) μB and demonstrate that the Cr charge-density wave gives rise to a
spin-density wave-type modulation of the magnetic moments with a long, doubled c-axis, periodicity (2c ≈ 69 Å).
The SrCrO3-δ vacancy mechanism may be relevant to related SOFC anode materials since Fe substitution stabilizes
the δ=0.2 superstructure at ambient pressure. Substituted Sr(Cr1-xFex)O3-δ phases with the same 15R structure were
obtained by solid state reaction at high temperature. HRPD@ISIS data show that the 15R-SrCr0.5Fe0.5O2.8 has a
partial cation ordering. The magnetic structure shows coexistence of two coupled magnetic propagation vectors (0,
0, 0) and (0, 0, 3/2) that vanish at TC=263(2) K.[2]
ICNS 2013 International Conference on Neutron Scattering
[1]
[2]
Arevalo-Lopez A. M. et al. Angew. Chem. Int. Ed. 51, 10791 (2012)
Arevalo-Lopez A. M. et al. Chem. Matter. Submitted
P.088 Frustration induced complex phase diagram in the spinel GeFe2O4
L Chaix1, E Ressouche2, C Colin3, V Simonet3, E Suard1, P Strobel3 and S de Brion3
1
Institut Laue Langevin, France, 2Institut de Nanosciences et Cryogénie, SPSMS/MDN, CEA-Grenoble,
France, 3Institut Néel, CNRS & Université Joseph Fourier, France
In the spinel compound GeFe2O4, crystallizing in the cubic space group Fd-3m, the magnetic Fe2+ ions are located
on a pyrochlore lattice. This material is thus potentially interesting in the fields of magnetic frustration and
multiferroicity. This study is part of a global project devoted to the Ge-based spinel family [1]. Macroscopic
measurements and neutron diffraction on GeFe2O4 powder and single-crystal under magnetic field up to 12 T, have
revealed a complex (H,T) phase diagram. In zero magnetic field, a first transition toward an incommensurate
magnetic arrangement with k2=(2/3+δ, 2/3+δ, 0) is observed at 8.4 K, followed by a second transition at 6.8 K to
a second magnetic phase with a commensurate k1=(2/3, 2/3, 0) propagation vector. In applied magnetic field
along different crystallographic axes, several transitions and domain reorientations are observed. A symmetry
analysis, using group theory, yields for the zero field magnetic structure 4 irreducible representations, all lacking an
inversion centre. The magnetic point group could then be non-centrosymmetric, a necessary condition for
multiferroicity.
[1]
Diaz et al., Phys Rev. B 74 (2006) 092404
P.089 Neutron diffraction and magnetic studies of La0.7La0.3Mn1-xMxO3 (M = Ni, Cr)
T Creel1, W Yelon1, O A Pringle1, W James1, M Kahveci1 and S Malik2
1
Missouri University of Science and Technology, USA, 2Universidade Federal de Rio Grande de Norte, Brazil
The effect of Ni and Cr substitution in La0.7La0.3Mn1-xMxO3 has been studied using neutron diffraction and
magnetization measurements. Neutron diffraction measurements were carried out on the position-sensitive detector
diffractometer at the University of Missouri Research Reactor. The Ni-substituted species show evolution from a
ferromagnetic metal to a charge ordered ferromagnet, while the Cr-substituted material evolves from a ferromagnetic
metal to a charge ordered ferromagnetic insulator and finally to a charge ordered antiferromagnet. Assuming that
the magnetic moments of each species remain constant, it is possible to model the fitted moments at all
concentrations. At low M concentration the Mn3+-Mn4+double exchange dominates and Ni (in the +3 state) couples
anti-parallel to the Mn moments. At x ≈ 0.2, the system undergoes a metal-insulator transition, and charge ordering
appears, leading to a doubled unit cell and new peaks (incorrectly identified by others as antiferromagnetic). The
Cr-doped system behaves quite differently. The Cr3+ moments couple parallel to the Mn3+ but anti-parallel to (and
flipping) the Mn4+ near neighbors. Charge ordering appears at x ≈ 0.2. At x ≈ 0.45 the system transforms to an
unusual charge ordered antiferromagnet in which the moments are anti-parallel in the successive layers, but the
concentrations of Mn3+ and Mn4+ are different in the two layers, leading to a small net moment.
2
ICNS 2013 International Conference on Neutron Scattering
P.090 Single crystal neutron diffraction study of the charge ordered phase of a true half-doped Pr1/2Ca1/2MnO3
charge ordered manganite
A Daoud-Aladine1, T Perring1, T Fernadez-Diaz2, J Rodriguez-Carvajal2 and R Ewings1
1
STFC Rutherford Appleton Laboratory, UK, 2Institut Laue Langevin, France
We have an expertise to treat diffraction data collected on micro-twinned manganites as if it was collected on a
single crystal. Back in 2002 [1], we’ve applied this to study the charge ordering (CO) phenomenon, discarding a
structural model seminally inferred by powder diffraction studies[2] reinterpreting CO as due to the formation of
ferromagnetic Mn+3.5-Mn+3.5 dimers sharing an electron (the Zener polarons)[1], rather than the admitted ionic CO of
Mn3+ and Mn4+ ions[2]. The distinction relied on our capacity, with our method, to measure and fit an order of
magnitude more superlattice reflections intensities than any other existing experimental technique, but a major
limitation was that we had only access to an “almost” prototype compound claimed to “a priori” show “almost” the
same CO phenomena than at half doping : it was indeed a Pr1-xCaxMnO3 crystal with x=0.4 slightly off the ideal
x=1/2 composition. For a decade, we could not verify if our structural model was valid at the right stoichiometry,
whilst most other techniques were still privileging the original CO scenario (resonant X-ray scattering, especially [3])
or more recently, apparently rule out any magnetic dimerization (inelastic neutron scattering [4]). We finally
obtained a truly half-doped Pr1/2Ca1/2MnO3 twinned crystal, from which we can very importantly ascertain that in its
paramagnetic phase at least, (TN<T<TCO) the ZP model obtained at x=0.4 [1] is still valid at x=1/2.
[1]
[2]
[3]
[4]
A.Daoud-Aladine et al, PRL 89 097205 (2002)
P.G.Radaelli et al, PRB 55 3015 (1997)
M. García-Fernández et al, PRL 103 097205 (2009)
G.E.Johnstone, et al, Phys. Rev. Lett. 109, 237202 (2012)
P.091 Study of spin and charge ordering in a single crystal of SrFeO3-d
C-H Du1, SH Lee1, T Frawley2, F C Chou3, P D Hatton2 and D J Huang4
1
Department of Physics, Tamkang University, Taiwan, 2Department of Physics, Durham University, UK, 3 CCMS,
National Taiwan University, Taiwan, 4National Synchrotron Radiation Research Center, Taiwan
Using magnetization, conductivity, and x-ray scattering measurements, we report the correlation between the giant
magnetoresistance and the charge and spin ordering in an iron-based oxide SrFeO3-d. SrFeO3 (SFO) has a cubic
structure with an isotropic metallic behavior. The cubic perovskite SrFeO3, in which iron is present as Fe4+, exhibits
the coexistence of metallic conductivity and screw-type antiferromagnetic ordering. However, the metallic state
found in SrFeO3 becomes unstable with respect to a charge disproportionation on Fe ions due to the oxygen
deficient. In order to understand this oxidation effect on the valance states of Fe and magnetoresistance, crystals
with different oxygen contents were grown by floating zone furnace. For this study, a crystal was characterized to
have a d 0.19 by transport measurements. From the conductivity and magnetization measurements, the crystal
shows two unusual transport behavior at T 120 K and 65 K. By the means of resonant x-ray scattering, including
soft and hard x-rays, the former is in accord with the formation of charge disproportionation distortion of Fe ions,
and the latter is the helical magnetic structure. The coupling of the helical magnetic structure and the lattice
distortion results in a complicated phase transition and a giant magnetoresistance at 65 K. A thermal hysteresis
transition is also observed, and can be understood as the consequence of the non-equilibrium thermal transition of
the domain-like charge modulations.
ICNS 2013 International Conference on Neutron Scattering
P.092 Temperature evolution of spin excitations of charge-strip ordered La2NiO4.11 into the disordered phase
P Freeman1, R Mole2, D Prabhakaran3 and C Niedermayer4
1
EPFL LQM, Switzerland, 2ANSTO, Australia, 3University of Oxford, UK, 4Paul Scherrer Institut, Switzerland
The importance of charge stripes for hole doped cuprate superconductivity has been under investigation since their
discovery in a hole doped cuprate[1]. Hole doped cuprates have a distinctive hourglass spin wave dispersion [2],
one way to understand the hourglass dispersion is in terms of the charge stripe picture[3,4]. While the ground state
magnetic excitations of many cuprate and charge-stripe order materials are known, far less is known about the
temperature evolution of the magnetic excitations. Here we report on the temperature dependence of the magnetic
excitations in La2NiO4.11 from base temperature to well above the magnetic ordering temperature into the stripe
liquid phase. We will concentrate on our latest results showing how the magnetic excitation spectrum adapts to the
well known change in the charge-stripe order periodicity as the magnetic order melts[5].
[1]
[2]
[3]
[4]
[5]
J. M. Tranquada et al. Nature (London) 375 (1995) 561
S. M. Hayden, et. al. , Nature London 429, (2004) 531
J. M. Tranquada, et. al., Nature London 429 (2004) 534
A. T. Boothroyd, et. al., Nature 375 (2011) 561
R. Kajimoto, et. al., Phys. Rev. B 64 (2011) 144432
P.093 One-dimensional dynamic symmetry in the cubic antiferromagnet RbMnF3
A Hoser1 and U Köbler2
1
Helmholtz-Zentrum Berlin, Germany, 2FZ Jülich, Germany
It is shown that thermal decrease of the order parameter of cubic RbMnF3 (TN=82.4 K) is excellent described by
universal T5/2 function up to ~70 K. T5/2 universality class is known from one-dimensional (1D) antiferromagnets
such as MnF2. Since magnon dispersions are isotropic in MnF2 and in RbMnF3 the dimensionalities of the order
parameter and magnon dispersions disagree. This shows that one has to distinguish between the local symmetry of
magnons and the global symmetry of the order parameter. As we know from Renormalization Group theory, spins
and interactions between spins are not important for the dynamics of the ordered state. This means that thermal
energy is no longer in the spin system but has changed to the delocalized excitations of the continuous magnetic
medium. Quite generally, the excitations of a continuous medium are bosons. The bosons of the continuous magnet
can be supposed to be essentially magnetic dipole radiation emitted upon precession of the ordered moments.
Change of thermal energy from interacting spins to the boson field is an example of a spontaneously broken
symmetry. In the isolated magnetic domain the boson field is one-dimensional. In order that the dynamics of the
macroscopic sample is isotropic an averaging process over all domains is necessary. Condition for the averaging
process is that the mean free path of the field bosons is larger than the size of the domains. In RbMnF3 domains are
larger than the mean free path of the GSW bosons. As a consequence, the macroscopic sample consists of
decoupled domains and shows 1D dynamic symmetry.
4
ICNS 2013 International Conference on Neutron Scattering
P.094 Modification of magnetic structure by intercalation of non-magnetic Na into FeOCl
S K Karna1, C M Wu1, C W Wang1, W H Li1, C G Wu2, I Jarrige3 and J W Lynn4
1
Department of Physics, National Central University, Taiwan, 2Department of Chemistry, National Central University,
Taiwan, 3Japan Atomic Energy Agency, Japan, 4NIST Center for Neutron Research, National Institute of Standards
and Technology, USA
Crystallographically layered compounds have recently received considerable attention, because of their
distinguished physical properties arising from the quasi-two-dimensional (Q2D) nature.The Q2D nature, resulting
from the presence of Van der Waals crystallographic gaps, has made this class of materials a good host for
accommodating guest molecules. In this article, we present on the magnetic ordering of the Fe ions in Naintercalated FeOCl by neutron diffraction and ac magnetic susceptibility measurements. The Na-intercalated FeOCl
compound crystallizes into an orthorhombic structure with space group Pmnm, as the parent compound does. Naintercalation results in the appearance of a peak at around 22 K in the temperature dependence of the in-phase
component of the ac magnetic susceptibility. This peak shifts to a lower temperature under an applied magnetic
field, indicating an antiferromagnetic character for these magnetic responses. Neutron magnetic diffraction
experiments reveal that ordering of the Fe spins develops below 90 K with a non-collinear spin configuration in
contrast to the spiral magnetic structure for the Fe spins in FeOCl. X-ray spectroscopic studies are also carried out to
observe the effects on the electronic structure of FeOCl due to Na intercalation.
P.095 Interplay between magnetism and charge correlation in highly-doped layered manganite
M Kubota1 and D Akahoshi2
1
JAEA, Japan, 2Toho University, Japan
Abstract unavailable
P.096 Crystal structure and magnetic ordering of new mixed valence LiMn2TeO6 compound
A Kurbakov1, V Nalbandyan2, V Chernyshev3, A Malyshev1 and E Tserkovnaya1
1
Petersburg Nuclear Physics Institute, National Research Centre, Russia, 2Southern Federal University,
Russia, 3Moscow State University, Russia
LiMn2TeO6 is a rare example of Mn compounds with mixed oxidation state <3, where Mn2+ and Mn3+ do not show
distinctly different coordination preferences. Possessing such Mn valency this compound is very differs from similar
materials exhibiting CMR, but with Mn oxidation degree between 3 and 4 which are intensively studied last years.
Crystal structure of LiMn2TeO6 by x-ray and neutron powder diffraction is triclinically distorted variant of well-known
orthorhombic Li2TiTeO6-type structure with another variant of cations ordering. Triclinic deformation is so big that
allows to consider LiMn2TeO6 as independent nonorthorhombic type. The structure is based on a distorted two-layer
close packing of O anions with Mn and Te occupying one half of the octahedral voids. It is established that the
model with two Mn2+ and two Mn3+ per unit cell is insufficient to describe the crystal structure, and it is necessary to
consider 5 possible Mn positions accepting the possibility of Mn and Li partitioning. Neutron diffraction data allow
to precisely define distribution of Mn ions and localize Li positions. Complex commensurate magnetic structure is
revealed in the range T=1.8-14K. Transition to incommensurable structures which finishes at 20K (TN) is observed
above 14K. Neutron results are in good agreement with temperature dependences of magnetic susceptibility and
specific heat which is complex and reveals the presence of two distinct anomalies at the same temperatures (14
and 20K). This work was supported by RFBR grant 11-03-01101.
ICNS 2013 International Conference on Neutron Scattering
P.097 Structural study of Tb3Fe5O12 using a newly built large area curved position-sensitive detector based
diffractometer at HANARO
C-H Lee1,2, Y Noda3, M Moon2, S A Kim2, S B Kim4 and H Haruhiro5
1
Korea Atomic Energy Research Institute, Korea, 2Neutron Science Division, Korea Atomic Energy Research Institute,
Korea, 3Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan, 4ACE Center,
Konyang University, Korea, 5Institute of Materials Research, Tohoku University, Japan
Neutron single crystal diffraction is indispensible for crystal and magnetic structure studies of materials. A new
neutron diffractometer with a large area, curved position-sensitive detector (C-2DPSD) has been installed recently
at HANARO under the collaboration with Tohoku university. The detector C-2DPSD covers 110° x 54° in horizontal
and vertical directions respectively with a nominal radius of 530mm, and its position decoding in (X, Y) positions is
done by the delay-line methods with a total delay-time of 270 ns, whose resolution is of 2mm/pixel, about 0.2
degree each. The diffractometer has mosaic Ge(311) surface normal monochromator with takeoff 41°, which
gives three wavelengths of 2.240, 1.153 and 0.780 Å. It is equipped with two m2 super-mirror vacuum beam paths
before and after the monochromator, 2 axis goniometers with an Euler cradle, and custom designed sample
chambers with a magnetic bearing for room temperature and low temperature measurements to reduce severe air
scattering toward the wide open area of C-2DPSD.
Raw data is analyzed by the program package, Reciprocal Analyzer. The perovskite type structure of the CMR
(Colossal Magneto Resistance) material of (Sm0.55Sr0.45)MnO3, and magnetic structure of terbium iron garnet of
cubic lattice constant of 12.436 Å are presented to demonstrate its performance and applications.
P.098 Reinvestigation of magnetic structure for Li2MnO3 with muons and neutrons
H Nozaki1, K Mukai1, M Harada1, M Mansson2, K Kamazawa3, D Andreica4, A Amato5 and J Sugiyama1
1
Toyota Central Research and Development Laboratories, Inc., Japan, 2ETH Zurich, Switzerland, 3Comprehensive
Research Organization for Science and Society, Japan, 4Babes-Bolyai University, Romania, 5Paul Scherrer Institut,
Switzerland
Magnetically, Li2MnO3 is known to be an antiferromagnetic (AF) insulator with TN 50 K. Past neutron work
proposed A-type AF order for Li2MnO3 [1]. However, since another possible structure was also suggested, the AF
spin structure is, to our knowledge, not fully understood at present. Therefore, we have performed muon-spin
rotation and relaxation (μ+SR) to deduce a correct AF spin structure from a microscopic view point [3]. Below TN,
the zero-field (ZF-) μ+SR spectrum showed a clear oscillation that consists of two muon-spin precession signals with
different frequencies. Combining with the dipole field calculations, it was found that the Cx-type AF order, in which
Mn moments align antiparallel along the c-axis both in the [Li1/3Mn2/3]O2 layer and between the adjacent
[Li1/3Mn2/3]O2 layers, but, in the [Li1/3Mn2/3]O2 layer, a ferromagnetic chain parallel to the a-axis aligns
antiferromagnetically along the b-axis, is the most probable spin structure for Li2MnO3.
[1]
[2]
6
M. H. Rossouw and M. M. Thackeray, Mat. Res. Bull. 26, 467 (1991)
J. Sugiyama et al., Phys. Rev. B 87, 024409 (2013)
ICNS 2013 International Conference on Neutron Scattering
P.099 Reverse Monte Carlo refinement of the nuclear and magnetic structure of FexO from total scattering data
P J Saines1, A K Cheetham2 and A L Goodwin1
1
Department of Chemistry, University of Oxford, UK 2Department of Materials Science and Metallurgy, University of
Cambridge, UK
Wüstite, FexO, is the most common non-silicate mineral in the earth and has an important affect on geological
processes [1]. Despite its simple rock salt structure it is universally non-stoichiometric, significantly affecting its
geologically relevant properties. The precise nature of the local defect structure, however, has been debated for the
last 50 years and remains unclear [2]. It is known that its Fe deficiency leads to vacancies on the octahedral Fe
sites and the formation of some Fe3+. Some of these Fe3+ cations occupy tetrahedral interstitial sites, which are
surrounded by four octahedral vacancies. Such defects agglomerate to form larger clusters and it is the preferred
growth directions of these larger clusters that lie at the heart of the debate.
In this study we have examined the nuclear and magnetic structures of Fe0.902O using Reverse Monte Carlo (RMC)
refinements of neutron total scattering powder diffraction data, which has been proven to be a powerful tool for
examining a wide range of materials. In this case the details of the refined models suggests a clear indication of the
preferred direction of growth of the larger clusters along with the bonding environments of the octahedral and
tetrahedral iron cations. Refinements of low temperature data also provide insight into the magnetic structure of
both the octahedral cations and, for the first time, the interstitial tetrahedral cations.
[1]
[2]
R.E. Cohen et al., Science 275, 654 (1997); b) J. Zhang, Phys. Rev. Lett.84, 507 (2000)
F. Koch et al., Acta Cryst.B25, 275 (1969); b) A.K. Cheetham et al., J. Phys. C4, 2160 (1971); c) T.R.
Welberry et al., Phys. Chem. Minerals24, 24 (1997)
P.100 Phase separation of complex half-doped 154Sm0.32Pr0.18Sr0.5MnO3 manganite
G Sarapin1, A Kurbakov1, V Ryzhov1, V Runov1, C Martin2 and A Maignan2
1
Petersburg Nuclear Physics Institute, National Research Centre, Russia, 2Laboratoire CRISMAT, Universite de Caen,
France
Earlier, from researches of Sm0.5Sr0.5MnO3 and Pr0.5Sr0.5MnO3 compounds were obtained that the replacement of Sm
by Pr or vice versa can drastically change the magneto-transport properties of manganites. By methods of neutron
powder diffraction, neutron depolarization, temperature dependences of magnetization, its second harmonic and
resistivity was studied phase separation and microscopic nature of the magnetoresistance in Sm 0.32Pr0.18Sr0.5MnO3
manganite. Existence of structural phase transition at 170K from high temperature Pbnm orthorhombic phase to a
mixture of two phases: orthorhombic Pbnm and monoclinic Р21/m, with coherently coupled by atomic in the unit
cell, but with different lattice parameters was revealed. Analysis of the magnetic contribution indicates that ground
magnetic state is a phase separate with a mixture of three magnetic phases: ferromagnetic (TC~300К), A-type
antiferromagnetic (TNA≈170К) and antiferromagnetic charge ordering pseudo-CE-type (TNCE≈120К) arising
because of the strong competition between the mechanisms of localization and delocalization of charges. F ordering
corresponds to the weakly deformed high-temperature Pbnm phase. Both AF states correspond to monoclinic
crystal structure, strongly compressed along c-axis. As a result, the microscopic nature of the
magnetoresistance,which is reflected in decrease the ρ by several orders at applying magnetic field 7T is described.
This work was supported by RFBR grant No. 12-02-00073.
ICNS 2013 International Conference on Neutron Scattering
P.101 Effect of Cr doping in the magnetic ordering of GaFeO3
R Singh1, A Das1, I Dhiman2, A K Nigam3 and S S Meena1
1
Bhabha Atomic Research Centre, India, 2Helmholtz-Zentrum Berlin für Materialien und Energie, Germany, 3Tata
Institute of Fundamental Research, India
Abstract unavailable
P.102 Magnetic ordering in Cu1-xNixCr2O4 mixed spinel
M Tovar, D M Toebbens and M Reehuis
Helmholtz-Zentrum Berlin für Materialien und Energie, Germany
The Jahn-Teller system Cu1-xNixCr2O4 exhibits several structural and magnetic phase transitions. At temperatures
between 310 and 865 K the cubic spinel structure (space group Fd3m) changes to a next lower symmetric
tetragonal structure with the space group I41/amd. In a narrow composition range of 0.75 < x < 0.90 one finds an
additional phase transition at about 300 K to an orthorhombic structure with the space group Fddd. In order to
investigate the interplay between the structural changes and the magnetic ordering we have determined the
ferrimagnetic structure of orthorhombic Cu0.15Ni0.85Cr2O4 from several neutron powder diffraction patterns collected
between 2 K and the ordering temperature of TC = 150 K. It was shown that the magnetic order of the ions located
at the tetrahedral Cu/Ni-site is much weaker pronounced than that of the octahedrally coordinated Cr-ions reaching
a saturation moment of 2.59(3) mB at 2 K. Here one finds a ferromagnetic component along the b-axis, while the
components within the ac-plane are antiferromagnetically coupled. The results are compared with those obtained
for the tetragonal phases as given in the magnetic phase diagram.
P.103 Complex magnetic couplings and in multiferroic Co3TeO6
C-W Wang, C-H Lee and W-H Li
Center for Neutron Beam Applications, National Central University, Taiwan
Cobalt tellurate Co3TeO6 has been characterized as a type-II multiferroic, where the close interplay between the
electric and magnetic order parameters may generate complex but interesting physical properties of the compound.
It is known that materials with magnetoelectric coupling, such as type-II multiferroics, are potentially important for
spintronics applications.
The powder and single crystal neutron diffraction experiments were conducted, exploring the magnetic and the
magnetoelectric properties of this compound. A non-collinear arrangement of the Co spins is found, and the
complex magnetic structure is understood by considering the geometrical arrangement of severely distorted CoO6
octahedra and CoO4 tetrahedra. The complex cobalt sublattice can be constructed with wavy honeycomb webs and
zigzag chains, which are composed of crystallographically distinct cobalt sites. We conclude the commensurate
magnetic order is described by a C2'/c symmetry. A Neel phased antiferromagnetic spin arrangement is observed
on the honeycombweb.
Measurements of the magnetic diffraction peak intensities from single crystal sample under an applied electric field
are carried out using the neutron triple axis spectrometer. Enhancement of the commensurate magnetic order
parameters by an applied electric field is also demonstrated, while the incommensurate component is found to be
insensitive to the applied electric field. In addition, a negative thermal expansion of the crystalline unit cell is
identified when electric polarization develops. Above observations suggest there exist complex magnetoelectric and
also the spin-lattice interactions in the compound.
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ICNS 2013 International Conference on Neutron Scattering