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We report two new rare-earth (R) ternary intermetallic compounds—Ho2Ni0.8T1.2 with T = Si and Ge—that correspond to the R5Ni2T3 phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr2Ni1–xP-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho2Ni0.8T1.2 with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R2Ni0.8T1.2 compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr2Ni1–xP structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at TC = 38 K for Ho2Ni0.8Si1.2 and TC = 37 K for Ho2Ni0.8Ge1.2, which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below TC with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ1 = [0, 0, 0]. Below TN ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ2 = [κx, 0, 0] appears to coexist with the first magnetic structure., The crystal structure of Ho2Ni0.8Si1.2 (and Ho2Ni0.8Ge1.2) [Zr2Ni0.48P-type (oP32-Pnma)] viewed along the b axis is given. The Ho, Ni1, Ni2/Si, Si1 and Si2 atoms are represented as red, turquoise, blue, light-gray, and dark-gray spheres, respectively. The distinctive structural fragment is built up of five differently oriented trigonal prisms. The magnetic structure of Ho2Ni0.8Ge1.2 with the antiferromagnetic component in the c direction and the ferromagnetic component along the a axis.

and presentation of a contributed talk at the MRS 2022 Spring Meeting in Symposium SF01: Materials Research Needs to Advance Nuclear Fuels, Structural Materials and Wasteforms ---Abstract--- The principal type of nuclear fuel material, which remains widely used today, is uranium dioxide (UO2). After discharge from a nuclear reactor some sort of disposal scenario needs to be considered to manage the spent fuel in a sustainable and safe way during extensive periods of time. However, in most countries which employ(ed) commercial nuclear energy, no political decision has yet been made, leading to prolonged intermediate storage periods up to several decades. As a result, oxidation and corrosion reactions due to accidental interaction between air, water, or moisture and the spent fuel need to be considered and understood. The response of conventional nuclear fuel to oxidation and corrosion is determined mainly by the physico-chemical properties of uranium. The binary uranium-oxygen system displays a very complex landscape of oxide phase fields. At temperatures below about 450 °C two single-valence compounds, uranium(IV) oxide (UO2) and uranium(VI) oxide (UO3), and several mixed-valence compounds (U4O9, U3O7, U3O8) can occur [1-4], characterized by particular associations of oxygen interstitials and vacancies. At higher temperature, long-range correlations among defects become less effective and the phase diagram becomes simpler, displaying a wide phase domain of nonstoichiometric UO2±x [5]. A characteristic feature of these higher oxide compounds lies in their crystallographic modifications, which occur almost exclusively in the anion sublattice, where point defects arrange into larger clusters to form complex long-range ordered structures [6-8]. However, despite sustained efforts for almost a century, the transition and structural relations between the different compounds is yet to be fully understood. New perspectives on the oxidation behavior of UO2 were obtained by investigating the kinetic mechanisms of these materials at the nanoscale, where fundamental differences were reported compared to the macroscale observations. Recent breakthroughs were made possible by using nanoscale imaging techniques like transmission electron microscopy [9], and by evaluating atomistic models of crystal structures [8,10,11]. A key instrument has been the application of neutron scattering techniques, owing to its sensitivity towards the anion sublattice [10], and its selectivity in probing magnetic transitions [12] and the local structure [13]. In this contribution we will report our current understanding of the uranium oxide systems U3O7 and U3O8 in ground state, based on latest neutron scattering data and ab-initio calculations. References [1] Grenthe I., et al., "Uranium", in: Morss L.R., Edelstein N.M., F. J. (Eds.) The Chemistry of the Actinide and Transactinide Elements, Springer, Dordrecht, 2008. [2] K.O. Kvashnina, et al., Phys. Rev. Lett., 111 (2013) 253002. [3] D.A. Andersson, et al., Inorg. Chem., 52 (2013) 2769. [4] S.D. Conradson, et al., Phys. Rev. B, 96 (2017) 125114. [5] P.Y. Chevalier, et al., J. Nucl. Mater., 303 (2002) 1. [6] B.T.M. Willis, J. Chem. Soc., Faraday Trans. II, 83 (1987) 1073. [7] L. Desgranges, et al., Inorg. Chem., 48 (2009) 7585. [8] G. Leinders, et al., Inorg. Chem., 55 (2016) 9923. [9] G. Leinders, et al., Inorg. Chem., 55 (2016) 3915. [10] G. Leinders, et al., Inorg. Chem., 60 (2021) 10550. [11] A. Soulié, et al., Inorg. Chem., 58 (2019) 12678. [12] A. Miskowiec, et al., Phys. Rev. B, 103 (2021) 205101. [13] L. Desgranges, et al., Inorg. Chem., 56 (2017) 321., {"references":["Grenthe I., et al., \"Uranium\", in: Morss L.R., Edelstein N.M., F. J. (Eds.) The Chemistry of the Actinide and Transactinide Elements, Springer, Dordrecht, 2008.","K.O. Kvashnina, et al., Phys. Rev. Lett., 111 (2013) 253002.","D.A. Andersson, et al., Inorg. Chem., 52 (2013) 2769.","S.D. Conradson, et al., Phys. Rev. B, 96 (2017) 125114.","P.Y. Chevalier, et al., J. Nucl. Mater., 303 (2002) 1.","B.T.M. Willis, J. Chem. Soc., Faraday Trans. II, 83 (1987) 1073.","L. Desgranges, et al., Inorg. Chem., 48 (2009) 7585.","G. Leinders, et al., Inorg. Chem., 55 (2016) 9923.","G. Leinders, et al., Inorg. Chem., 55 (2016) 3915.","G. Leinders, et al., Inorg. Chem., 60 (2021) 10550.","A. Soulié, et al., Inorg. Chem., 58 (2019) 12678.","A. Miskowiec, et al., Phys. Rev. B, 103 (2021) 205101.","L. Desgranges, et al., Inorg. Chem., 56 (2017) 321."]}

Two $\mathrm{CaMn}B\mathrm{Sb}{\mathrm{O}}_{6}$ ($B=\mathrm{Cr}$ and Fe) high-pressure double double perovskites are reported. Spins in $\mathrm{Ca}\mathrm{Mn}\mathrm{Cr}\mathrm{Sb}{\mathrm{O}}_{6}$ order below ${T}_{\mathrm{C}}=49\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ into a collinear ferrimagnetic arrangement with spins in the $xy$ plane. $\mathrm{Ca}\mathrm{Mn}\mathrm{Fe}\mathrm{Sb}{\mathrm{O}}_{6}$ has the same ordered magnetic structure below ${T}_{\mathrm{C}1}=55$ K, but also shows a second magnetic transition at ${T}_{\mathrm{C}2}=21\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ where the spins reorient towards the $z$ axis. This may reflect a greater degree of magnetic disorder for $B=\mathrm{Fe}$ and A-B intersite charge transfer may also be significant.

Ozone oxidation has allowed the stabilization of a very high iron oxidation state in the FeSr2YCu2O7.85 cuprate, in which a long-range magnetic ordering of the high valent iron cations coexists with the superconducting interactions (magnetic ordering temperature TN = 110 K > superconducting critical temperature Tc = 70 K). The somewhat unexpected A-type AFM structure, with a μ(Fe) ∼ 2 μB magnetic saturation moment associated with the hypervalent iron sublattice, suggests an unusual low spin state for the iron cations, while the low dimensionality of the magnetic structure results in a soft switching toward ferromagnetism under small external magnetic fields. The role of the crystal structure and of the high charge concentration in the stabilization of this unusual electronic configuration for the iron cations is discussed.

High resolution and high intensity neutron powder diffraction are used to determine the temperature dependence of the crystallographic and magnetic structure of the orthoferrite CeFeO3. The high temperature G x -type magnetic coupling of the Fe-sublattice described by the Γ4 (G x A y F z ) irreducible representation changes at the spin reorientation temperature T SR = 228 K to a G y -type coupling of Γ1 (A x G y C z ). The spin reorientation is of first order and sees a hysteresis of about 2.5 K at T SR. Below 35 K faint magnetic peaks reflecting C z type magnetic coupling appear and are argued to be related to the Ce-sublattice. Magnetic moments at 2 K amount to μ Fe = 4.15 μ B and μ Ce = 0.11 μ B. CeFeO3 is only the second RFeO3 compound after DyFeO3 showing this ground state magnetic structure of the Fe-sublattice. The orthorhombic structure Pbnm is kept over the whole temperature range.

The R 3TiSb5 ternary compounds, with R a light rare earth (La to Sm) have been reported to crystallize with the anti-Hf5CuSn3-type hexagonal structure (Pearson’s symbol hP18; space-group P63/mcm, N. 193). An early article that reported possible superconductivity in some of these intermetallic phases (namely those with R = La, Ce, and Nd) caught our attention. In this work, we have now refined the crystal structure of the R 3TiSb5 compounds with R = Ce, Pr and Nd by Rietveld methods using high-resolution neutron powder diffraction data. The magnetic ground states of these intermetallics have been investigated by low-temperature magnetization and high-intensity neutron diffraction. We find two different magnetic transitions corresponding to two related magnetic structures at T N1 = 4.8 K (k 1 = [0, 1/2, 1/8]) and T N2 = 3.4 K (k 2 = [0, 0, 1/8]), respectively for Ce3TiSb5. However, the magnetic ordering appears to occur following a peculiar hysteresis: the k 2-type magnetic structure develops only after the k 1-type phase fraction has first slowly ordered with time and the size of the ordered Ce3+ magnetic moment has become large enough to induce the second magnetic transition. At T = 1.5 K the maximum amplitude of the Ce moment in the coexisting phases amounts to μ Ce = 2.15 μ B. For Nd3TiSb5 an antiferromagnetic ordering below T N = 5.2 K into a relatively simpler commensurate magnetic structure with a magnetic moment of μ Nd = 2.14(3) μ B and magnetic propagation vector of k = [0, 0, 0], was determined. No evidence of superconductivity has been found in Nd3TiSb5. Finally, Pr3TiSb5 does not show any ordering down to 1.5 K in neutron diffraction while an antiferromagnetic ground state is detected in magnetization measurements. There is no sign of magnetic contribution from Ti atoms found in any of the studied compounds.

We report muon spin rotation (mu SR) and neutron diffraction on the rare-earth-based magnets (Mo2/3RE1/3)2AlC, also predicted as parent materials for two-dimensional (2D) derivatives, where the rare earth (RE) = Nd, Gd (only mu SR), Tb, Dy, Ho, and Er. By crossing information between the two techniques, we determine the magnetic moment (m), structure, and dynamic properties of all compounds. We find that only for RE = Nd and Gd the moments are frozen on a microsecond timescale. Out of these two, the most promising compound for a potential 2D high m magnet is the Gd variant, since the parent crystals are pristine with m = 6.5 +/- 0.5 mu B, Neel temperature of 29 +/- 1 K, and the magnetic anisotropy between out-of- and in-plane coupling is smaller than 10-8. This result suggests that magnetic ordering in the Gd variant is dominated by in-plane magnetic interactions and should therefore remain stable when exfoliated into 2D sheets. Funding Agencies|Israel Atomic Energy Commission Pazy Foundation grant; Knut and Alice Wallenberg (KAW) FoundationKnut & Alice Wallenberg Foundation; Flag-ERA JTC 2017 project "MORE-MXenes"

International audience; Two M2(SeO3)F2 fluoro-selenites (M = Mn 2+ , Ni 2+) have been synthesized using optimized hydrothermal reactions. Their 3D framework consists of 1D-[MO2F2] 4chains of edge-sharing octahedra with a rare topology of O-O and F-F alternating µ2 bridges. The inter-chain corner sharing connections are assisted by the mixed O vs. F anionic nature and develop a complex set of M-X-M super-exchanges calculated by LDA+U. Their interplay induce prominent in-chain antiferromagnetic frustration while the interchain exchanges are responsible for the cycloidal magnetic structure observed below TN ~21.5 K in the Ni 2+ case. For comparison the Mn 2+ compound develops a nearly collinear spin (canted) ordering below TN ~26 K with ferromagnetic chain-units.

We report magnetic properties of a $3{d}^{9}$ $({\mathrm{Cu}}^{2+})$ magnetic insulator ${\mathrm{Cu}}_{2}{\mathrm{OSO}}_{4}$ measured on both powder and single crystal. The magnetic atoms of this compound form layers whose geometry can be described either as a system of chains coupled through dimers or as a kagome lattice where every third spin is replaced by a dimer. Specific heat and DC susceptibility show a magnetic transition at 20 K, which is also confirmed by neutron scattering. Magnetic entropy extracted from the specific heat data is consistent with an $S=1/2$ degree of freedom per ${\mathrm{Cu}}^{2+}$, and so is the effective moment extracted from DC susceptibility. The ground state has been identified by means of neutron diffraction on both powder and single crystal and corresponds to an $\ensuremath{\sim}{120}^{\ensuremath{\circ}}$ spin structure in which ferromagnetic intradimer alignment results in a net ferrimagnetic moment. No evidence is found for a change in lattice symmetry down to 2 K. Our results suggest that ${\mathrm{Cu}}_{2}{\mathrm{OSO}}_{4}$ represents a type of model lattice with frustrated interactions where interplay between magnetic order, thermal and quantum fluctuations can be explored.

The GaV$_4$S$_{8-y}$Se$_y$ $(y = 0$ to $8)$ family of materials have been synthesized in both polycrystalline and single crystal form, and their structural and magnetic properties thoroughly investigated. Each of these materials crystallizes in the $F\bar{4}3m$ space group at ambient temperature. However, in contrast to the end members GaV$_4$S$_8$ and GaV$_4$Se$_8$, that undergo a structural transition to the $R3m$ space group at 42 and 41 K respectively, the solid solutions $(y = 1$ to $7)$ retain cubic symmetry down to 1.5 K. In zero applied field the end members of the family order ferromagnetically at 13 K (GaV$_4$S$_8$) and 18 K (GaV$_4$Se$_8$), while the intermediate compounds exhibit a spin-glass-like ground state. We demonstrate that the magnetic structure of GaV$_4$S$_8$ shows localization of spins on the V cations, indicating that a charge ordering mechanism drives the structural phase transition. We conclude that the observation of both structural and ferromagnetic transitions in the end members of the series in zero field is a prerequisite for the stabilization of a skyrmion phase, and discuss how the absence of these transitions in the $y = 1$ to $7$ materials can be explained by their structural properties., Main text: 14 pages, 5 figures, 1 table. Supplementary information: 10 pages, 6 figures, 6 tables

Acknowledgements We acknowledge the University of Aberdeen for provision of a studentship for Harriet Hopper and the Higher Education Commission of Pakistan for providing a visiting fellowship for Dr. Falak Sher.

Barlowite, ${\mathrm{Cu}}_{4}{(\mathrm{OH})}_{6}\mathrm{FBr}$, has attracted much attention as the parent compound of a new series of quantum spin-liquid candidates, ${\mathrm{Zn}}_{x}{\mathrm{Cu}}_{4\ensuremath{-}x}{(\mathrm{OH})}_{6}\mathrm{FBr}$. While it is known to undergo a magnetic phase transition to a long-range ordered state at ${T}_{N}=15$ K, there is still no consensus over either its nuclear or magnetic structures. Here, we use comprehensive, high-flux powder neutron diffraction studies on deuterated samples of barlowite to demonstrate that the only space group consistent with the observed nuclear and magnetic diffraction at low temperatures is the orthorhombic $Pnma$ space group. We furthermore conclude that the magnetic intensity at $Tl{T}_{N}$ is correctly described by the $P{n}^{\ensuremath{'}}{m}^{\ensuremath{'}}a$ magnetic space group, which crucially allows the ferromagnetic component observed in previous single-crystal and powder magnetization measurements. As such, the magnetic structure of barlowite resembles that of the related material clinoatacamite, ${\mathrm{Cu}}_{4}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}$, the parent compound of the well-known quantum spin-liquid candidate hebertsmithite, ${\mathrm{ZnCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}$.

We have investigated the magnetic properties of a polycrystalline sample of NdOs2Al10 using neutron diffraction and inelastic neutron scattering, magnetic susceptibility and heat capacity measurements. The magnetic susceptibility data reveal an antiferromagnetic transition at T N1 = 2.2 K while the heat capacity data which extend to lower temperatures show a further transition at T N2 = 1.1 K. The INS measurements detect four well-resolved crystal field excitations at 7.4, 12.4, 17.6 meV and 19.2 meV at 5 K. The positions and intensities of the observed CEF excitations and the temperature dependence of previously published single crystal susceptibility data are analysed based on the orthorhombic CEF model of the J = 9/2 ground state multiplet of Nd3+ ion. The neutron diffraction study reveals the magnetic structure at T = 1.6 K to be of sine wave type (κ = [0, 0.723, 0]) with an ordered state moment of μ Nd 3+ = 1.59(1) μ B aligned along the a-axis in agreement with the single ion crystal field anisotropy. This indicates that the magnetism of NdOs2Al10 is governed by the RKKY interactions in agreement with other RT 2Al10 (R = Nd, Sm, Tb, T = Fe, Ru and Os), but different to that of R = Ce based compounds where anisotropic two ions interaction as well as Kondo interaction govern the anomalous direction of the ordered state moment.

The perovskite polymorph of Mn(2)CrSbO(6) compound has been synthesized at 8 GPa and 1473 K. It crystallizes in the monoclinic P21/n space group with cell parameters a = 5.2180 (2) Å, b = 5.3710(2) Å, c = 7.5874(1) Å and β = 90.36(1)°. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn(2+) and Cr(3+) sublattices below TN = 55 K with a small canting. Low temperature powder neutron diffraction reveals a commensurate magnetic structure with spins confined to the ac-plane and a propagation vector κ = [1/2 0 1/2]. The thermal treatment of this compound induces an irreversible phase transition to the ilmenite polymorph, which has been isolated at 973 K and crystallizes in R3[combining macron] space group with cell parameters a = 5.2084 (4) Å and c = 14.4000 (11) Å. Magnetic susceptibility, magnetization and powder neutron diffraction data confirm the antiferromagnetic helical ordering of spins in an incommensurate magnetic structure with κ = [00 0.46] below 60 K, and the temperature dependence of the propagation vector up to κ = [00 0.54] at about 10 K.

An investigation on the ground state magnetism of CeScSi, CeScGe (tetragonal CeScSi-type, tI12, space group I4/mmm) by temperature-dependent powder neutron diffraction has been carried out, as debated and controversial data regarding the low temperature magnetic behaviours of these two compounds were reported. Our studies reveal that, while cooling, long-range magnetic ordering in CeScSi and CeScGe takes place by a two-step process. A first transition leads to a magnetic structure with the Ce moments aligned ferromagnetically onto two neighbouring tetragonal basal a-b planes of the CeScSi-type structure; the double layers are then antiferromagnetically coupled to each other along the c-axis. The transition temperature associated with the first ordering is T N ~ 26 K and T N ~ 48 K for the silicide and the germanide, respectively. Here the spin directions are rigorously confined to the basal plane, with values of the Ce magnetic moments of μ Ce = 0.8-1.0 μ B. A second magnetic transition, which takes place at slightly lower temperatures, results in a canting of the ordered magnetic moments out of the basal plane which is accompanied by an increase of the magnetic moment value of Ce to μ Ce = 1.4-1.5 μ B. Interestingly, the second magnetic transition leads to a structural distortion in both compounds from the higher-symmetry tetragonal space group I4/mmm to the lower-symmetry and triclinic I-1 (non-standard triclinic). Magnetic symmetry analysis shows that the canted structure would not be allowed in the I4/mmm space group; this result further confirms the structural transition. The transition temperatures T S from I4/mmm to I-1 are about 22 K in CeScSi and 36 K in CeScGe, i.e. well below the temperature of the first onset of antiferromagnetic order observed in this work (or below the ordering temperature, previously reported as either T C or T N). This result, along with the synchronism of the magnetic and structural transitions, suggests a magnetostructural origin of this structural distortion. We have also carried out powder neutron diffraction for LaScSi as a non-magnetically-ordering reference compound and compared the results with those of CeScSi and CeScGe compounds.

The commensurate crystal structure of the magnetic phase occurring below 7 K of the multiferroic Pb2MnWO6 perovskite has been solved by the introduction of the superspace approach. This lead based double perovskite is characterized by a complex ferrielectric non-centrosymmetric nuclear structure with orthorhombic symmetry stable in a wide temperature range. As indicated from the analysis of powder neutron diffraction data, the low temperature antiferromagnetic structure showing a propagation vector k 1/4 [1/4 0 0] is stabilized by a multi-step process involving the evolution from incommensurate to commensurate spin ordering with a concomitant change of the magnetic symmetry. The determination of the Pb2MnWO6 magnetic structure offers a meaningful example of the superspace application and provides a detailed phase diagram of the involved magnetic states. Nowadays this ordered perovskite could be considered as a new type of multiferroic material combining ferrielectric properties and a long period antiferromagnetic structure.

A systematic study of the physical properties and microscopic magnetism of Nd7Pd3 compound, which in the paramagnetic state crystallizes in the non-centrosymmetric hexagonal Th7Fe3-type structure (hP20-P63 mc; with a = 10.1367(1) A and c = 6.3847(1) A at 300 K), confirms multiple magnetic ordering transitions that occur upon cooling. Antiferromagnetic transition is observed at T N = 37 K, which is followed by ferromagnetic transformation at T C = 33 K. The first-order magnetic transition at T C is magnetoelastic: it involves a change of crystal symmetry from P63 mc to Cmc21 and leads to anisotropic changes of the unit cell parameters. While the antiferromagnetic structure is symmetry allowed in P63 mc, the ferromagnetic structure with magnetic moments along the a-direction of the original hexagonal unit cell induces the first order transition to Cmc21. Density functional theory calculations confirm the experimentally observed ground state with the a-axis as the easy magnetization direction.

The synthesis and structural and magnetic characterizations of K3Fe6F19, a new iron potassium fluoride with a complex tungsten bronze related structure, are presented. This phase was found during the investigation of relatively low-temperature (600 degrees C) synthesis conditions of classical tetragonal tungsten bronze (TTB) fluorides and can be considered an intermediate that forms at this temperature owing to faster crystallization kinetics. The K3Fe6F19 compound has an orthorhombic structure (space group Cmcm (63), a = 7.6975(3) angstrom, b = 18.2843(7) angstrom, c = 22.0603(9) angstrom) related to the TTB one, where the perovskite cage is substituted by a large S-shaped channel simultaneously occupied by two potassium atoms. The magnetic structure, characterized by magnetization measurements on an oriented single crystal and powder neutron diffraction, is dominated by the presence of interconnected double stripes of antiferromagnetic triangular exchange interaction patterns alternately rotated in clock- and anticlockwise fashion. The magnetic order takes place in a wide temperature range, by increasing progressively the interaction dimensionality.

We have investigated the magnetic properties of slightly doped multiferroic TbMnO3 after application of a magnetic field. The study focused on compositions TbMn1-xAxO3 (x ≤ 0.1) with A = Ga, Sc, Co and Al. The replacement of Mn by Ga, Al or Sc proved to be isovalent while the addition of Co leads to a partial charge transfer as Mn3+ + Co3+ → Mn4+ + Co2+. The samples with 10% of non-magnetic doping, TbMn0.9Sc0.1O3, TbMn0.9Al0.1O3 and TbMn0.9Ga 0.1O3, preserve the long range antiferromagnetic ordering of the Mn sublattice with, however, reduced transition temperatures compared to TbMnO3. New magnetic interactions in the Co-doped compound lead to the suppression of Mn ordering in TbMn0.9Co0.1O 3. The application of an external magnetic field produces similar metamagnetic transitions in all TbMn0.9A0.1O3 compounds that are ascribed to the Tb-sublattice. Powder neutron diffraction was used to determine the changes in the magnetic structure with applied magnetic field revealing a strong increase of F- and C-type magnetic reflections in these compounds. These results are accounted for by the anisotropic response of the Tb sublattice to a magnetic field while the Mn sublattice remains unchanged. © 2013 Published by Elsevier Masson SAS., Financial support from Spanish MEC (projects MAT2012-38213-C02-01 and MAT2011-27233-C02-02) and DGA (CAMRADS) is acknowledged.

The finding of new multiferroic materials, where electric and magnetic orders coexist, is a challenging task currently. The double perovskite Y${}_{2}$CoMnO${}_{6}$ shows spontaneous magnetization and electrical polarization at low temperature. Previous investigations of this compound did not reach agreement about the type of magnetic structure present. This study demonstrates that this compound exhibits a collinear ferromagnetic ordering of Co${}^{2+}$ and Mn${}^{4+}$ moments in the $a\phantom{\rule{0}{0ex}}c$ plane with a small antiferromagnetic canting along the $b$ axis. A thorough characterization of the dielectric properties reveals the absence of any related anomaly in the dielectric permittivity and the lack of spontaneous electrical polarization ($P$) in the $P$($E$, electric field) loops. The pyroelectric current is strongly dependent on the number of antisite defects in the Co/Mn arrangement, the heating rate, and the poling field. Thus, the observed electric polarization is due to thermally stimulated depolarization currents ascribed to defect dipoles mainly placed at the antiphase boundaries. No ferroelectric transition occurs in this material, disproving the existence of intrinsic magnetoelectric multiferroicity.

The thermal evolution of structural and magnetic details of the orthovanadate $\mathrm{TmV}{\mathrm{O}}_{3}$, studied in detail by neutron and synchrotron powder diffraction, is reported. Crystallizing in space group Pnma at room temperature, $\mathrm{TmV}{\mathrm{O}}_{3}$ undergoes a first structural phase transition to $P{2}_{1}/a$ at ${T}_{\mathrm{OO}}=180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, where a $G$-type orbital ordered state develops. At ${T}_{\mathrm{S}}=75\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, a change back to Pnma occurs, and the establishment of $C$-type orbital order takes place. The ${\mathrm{V}}^{3+}$ ions order antiferromagnetically with a magnetic propagation vector $\mathbf{k}=0$ below ${T}_{\mathrm{N}1}=105\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, while the $\mathrm{T}{\mathrm{m}}^{3+}$ sublattice orders at ${T}_{\mathrm{N}2}=20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ following the same propagation vector. Between ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{S}}$, a coexistence of $G$-type ($P{2}_{1}/a$) and $C$-type (Pnma) orbital ordered states exists. The $P{2}_{1}/a$ phase is magnetically separated into two fractions, which adopt a ${C}_{x}{C}_{y}0$ and ${G}_{x}00$ coupling, respectively, while the Pnma volume fraction follows a $0{G}_{y}0$ magnetic structure. At ${T}_{\mathrm{N}2}$, the appearance of the Tm sublattice magnetization ($0{C}_{y}0$) leads to a spin flop transition of the V sublattice from $0{G}_{y}0$ to ${G}_{x}00$. The results are presented and analyzed in the general context of the series of $R\mathrm{V}{\mathrm{O}}_{3}$ compounds, and they are used to discuss recent magnetization results.

The synthesis of the new compounds RMgSn (R = La–Nd, Sm, Gd–Tm, Lu and Y) has been recently reported. The compounds formed by La and Ce crystallise in the TiNiSi structure type ( oP 12, Pnma ), while from Nd they adopt the CeScSi-type ( tI 12, I 4/ mmm ); PrMgSn is dimorphic: its high-temperature form (HT) is TiNiSi-type while the low-temperature one (LT) is CeScSi-type. In this paper we now report the results of a neutron diffraction investigation which has been performed in order to refine the crystal as well as the magnetic structures for the RMgSn compounds with R = Ce, Pr, Nd and Tb. All these compounds see at low temperature the establishment of long range magnetic ordering with a predominantly antiferromagnetic interaction; only PrMgSn-HT orders ferromagnetically. These results agree with those from magnetic measurements recently reported. The magnetic structure of CeMgSn is of the amplitude-modulated type, the value of the magnetic propagation vector refined at 2 K is τ = [0, 0.1886(4), 0.3384(8)]. The PrMgSn-HT phase below T = 52 K adopts first a purely ferromagnetic structure, then at about T = 15 K a second magnetic coupling leads to a spin-canted magnetic structure. Both PrMgSn-LT and NdMgSn have the same antiferromagnetic commensurate magnetic structure. The TbMgSn compound below T N = 35 K orders antiferromagnetically with an equal moment cycloidal structure; however a second magnetic transition at a temperature corresponding to T N 2 = 65 K is likely also present.

In 1949 Shull et al. [1] used for the first time neutrons for the determination of a magnetic structure. Ever since, the need for neutrons for the study of magnetism has increased. Two main reasons can be brought forward to explain this ongoing success: First of all a strong rise in research on functional materials (founding obliges) and secondly the increasing availability of easy to use programmes for the treatment of magnetic neutron diffraction data. The giant magnetoresistance effect, multiferroic materials, magnetoelasticity, magnetic shape memory alloys, magnetocaloric materials, high temperature superconductivity or spin polarized half metals: The last 15 years have seen the event of all these “hot topics” where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms. Refinement programs like FULLPROF or GSAS and programs for magnetic symmetry analysis like BASIREPS or SARAH make the determination of magnetic structures accessible for non specialists. Following a historical overview on the use of neutron powder diffraction for the determination of magnetic structures, I will try to convince you of the easiness of using magnetic symmetry analysis for the determination of magnetic structures using some recent examples of own research on the rare earth iron borate TbFe3(BO3)4 and the rare earth transition metal telluride Ho6FeTe2.

Samples of mesoporous Co 3 O 4 , created by using mesoporous silicas KIT-6 and SBA-16 as hard templates to control the growth of Co 3 O 4 have been investigated with SQUID magnetometry and neutron powder diffraction, to reveal the effects of high surface area on the magnetic and electronic properties. DC magnetic susceptibility measurements show lower Neel ordering temperatures and lower magnetic moments than in a “bulk” reference. A lower second transition temperature is also observed in the mesoporous samples, associated with the freezing of the surface (shell) magnetic moments. Measurements taken with increasing applied field at constant temperature show the materials to be antiferromagnetic as expected. Complementary parametric neutron powder diffraction studies show similar trends between the two mesoporous samples when looking at their Neel temperatures, and verify long range order within the samples.

The ground state magnetic behaviour of Ce2(Pd0.8Ag0.2)2In and Ce2(Pd0.5Ag0.5)2In, found in the ferromagnetic branch of Ce2Pd2In, has been investigated by neutron powder diffraction at low temperature. Ce2(Pd0.8Ag0.2)2In is characterized by a ferromagnetic structure with the Ce moments aligned along the c-axis and values of 0.96(2) mB. The compound retains the P4/mbm throughout the magnetic transition, although the magnetic ordering is accompanied by a significant decrease of the lattice strain along [00l], suggesting a magnetostructural contribution. The magnetic behaviour of Ce2(Pd0.5Ag0.5)2In is very different; this compound exhibits an extremely reduced magnetic scattering contribution in the diffraction pattern, that can be ascribed to a different kind of ferromagnetic ordering, with extremely reduced magnetic moments (~ 0.1 mB) aligned along [0l0]. These results point to a competition between different types of magnetic correlations induced by Ag-substitution, giving rise to a magnetically frustrated scenario in Ce2(Pd0.5Ag0.5)2In., to be published in Journal of Physics: Condensed Matter

The magnetic structure of the Fe 2 P-type R 6 CoTe 2 phases ( R =Gd–Er, space group P 6¯2 m ) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: T C =220 K and T CN =180 K for Gd 6 CoTe 2 , T C =174 K and T CN =52 K for Tb 6 CoTe 2 , T C =125 K and T CN =26 K for Dy 6 CoTe 2 , T CN =60 K and T N =22 K for Ho 6 CoTe 2 and T CN ∼30 K and T N ∼14 K for Er 6 CoTe 2 . Between 174 and 52 K Tb 6 CoTe 2 has a collinear magnetic structure with K 0 =[0, 0, 0] and with magnetic moments along the c -axis, whereas below 52 K it adopts a non-collinear ferromagnetic one. Below 60 K the magnetic structure of Ho 6 CoTe 2 is that of a non-collinear ferromagnet. The holmium magnetic components with a K 0 =[0, 0, 0] wave vector are aligned ferromagneticaly along the c -axis, whereas the magnetic component with a K 1 =[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22 K coincides with the reorientation of the Ho magnetic component with the K 0 vector from the collinear to the non-collinear state. Below 30 K Er 6 CoTe 2 shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K 0 =[0, 0, 0] and K 1 =[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14 K corresponds to the variation in the magnitudes of the M Er K0 and M Er K1 magnetic components. In these phases, no local moment was detected on the cobalt site. The magnetic entropy of Gd 6 CoTe 2 increases from Δ S mag =−4.5 J/kg K at 220 K up to Δ S mag =−6.5 J/kg K at 180 K for the field change Δ μ 0 H =0–5 T.

The temperature magnetic phase diagrams, of the dimorphic DySi compound, have been studied in terms of wave vectors in the range 1.5–45 K, by neutron diffraction. The polycrystalline sample consists of 26% of CrB-type ( Cmcm no. 63, all atoms at 4c site: (0, y , 1/4)) and of 74% of FeB-type ( Pnma no. 62, all atoms at 4c site: ( x , 1/4, z )). The CrB-ordering is described by the wave vector: q 1 =(0, 0, 1/2) over the entire magnetically ordered regime with a uniaxial magnetic structure along the shortest axis c. The FeB-type magnetic phase diagram reveals three distinct regions of magnetic ordering below T N and one first order transition at T 2 =23.5 K (on heating). The ordering is described by two symmetry independent magnetic vectors q 2 =(0, 1/2, 1/6) and q 3 =(0, q 3 y , q 3 z ) with a temperature variable length. At 1.5 K q 3 y ≈1/2 and q 3 z ≈1/11. The two phases coexist in the form of domains. They differ in the moment orientation of the q 3 phase that deviates by ∼22° from the b -axis in the (0, 0, 1) plane. The low temperature range ( LT ) 1.5 K— T 2 subdivides into two regions: (i) LT -1, between 1.5 K— T 1 where the relative amount of the two phases remains unchanged and in (ii) LT -2: T 1 – T 2 where the amount of the incommensurate q 3 phase increases at the cost of the commensurate q 2 amplitude modulated structure which remains unchanged but fully disappears at the first order transition at T 2 =23.5 K. The q 3 phase undergoes minor changes until 22 K and gets destabilised at T 2 where the q 3 z component jumps from the LT value q 3 z ≈1/11 to the HT value ≈1/7 and the q 3 y component increases from 0.484(1) to 0.495(1). (iii) The high temperature ( HT ) range T 2 – T N ( T N =40±1 K) is described by a single wave vector q 3 . The disproportionation of the HT magnetic phase q 3 below T 2 into two coexisting distinct phases q 2 , q 3 down to 1.5 K is an unusual phenomenon, to our knowledge observed for the first time. Various mechanisms are discussed.

The low-temperature magnetic ordering of the dimorphic DySi compound has been studied at 1.5 K by neutron diffraction on two polycrystalline samples. The samples comprise various amounts of the two orthorhombic modifications: CrB-type (Cmcm Nr. 63, all atoms at 4c site: (0, y, 1 4 )) and FeB-type (Pnma Nr. 62, all atoms at 4c site: (x, 1 4 , z)), both order antiferromagnetically (TN≈38 K). The CrB-type phase orders with a uniaxial structure with the wave vector q1=(0, 0, 1 2 ) requiring a doubling of the c-axis. The Dy moments point along the linear chain with the shortest distance c. At 1.5 K, the ordered moment value is 8.57(1) μB/Dy atom. Two symmetry independent wave vectors describe the 1.5 K magnetic ordering of the FeB-type phase: q2=(0, 1 2 , 1 6 ) and q3=(0, 0.484(1), 0.0892(1)), coexisting in form of domains. In both structures the magnetic moments are confined to the (0 0 1) plane at an angle of 2(2)° and 22(3)° from the shortest axis b, respectively. Both structures correspond to sine wave modulations. The amplitude of the q2 wave is mo=7.5(1) μB/Dy atom and that of q3 8.2(1) μB/Dy atom. The wave vector q2 when referring to the (a, 2b, c) cell and the wave vector q=(0, 0, 1 6 ) corresponds to a transversal modulation, which by a proper origin choice can be also described as an antiphase domain structure with two amplitudes. The moments point to the b-axis and are stacked in the sequence (+mo/2, −mo/2, −mo, −mo/2, +mo/2, +mo, …) along the c-direction, while tb acts as an antitranslation. For the q3 phase, the local moment value depends on the atom position in the wave. We also discuss the case where q3 and q2 act simultaneously in physical space.

The crystallographic and magnetic structures of polycrystalline Ba2(Fe,W)2O6 and Ba2(Fe,W0.5Mo0.5)2O6 double-perovskites have been investigated by X-ray and neutron powder diffraction (NPD), magnetization and Mossbauer spectroscopy. The samples were synthesized by conventional solid-state reaction at temperatures about 1273 K. The compounds crystallize in the cubic structure with space group F m 3 ¯ m . The magnetic structures were determined by neutron powder diffraction between 5 K and 310 K. Evidence for an antiferromagnetic behavior has been observed for Ba2(Fe,W)2O6 with TN = 24.7 K and a two-phase separation for Ba2(Fe,W0.5Mo0.5)2O6 into an antiferromagnetic structure of the W-type with TN = 24.7 K and the ferromagnetic Mo-type with TC = 270 K.

Magnetic structures and magnetic phase transitions in natural-layered TbMn2(GexSi1−x)2 compounds have been studied by magnetisation, low-field AC-susceptibility, electrical resistivity and neutron-diffraction experiments. Non-collinear magnetic structures were observed in the concentration range 0 < x < 0.88. In compounds with x

We report measurements performed on a polycrystalline sample of the pyrochlore compound ${\mathrm{Nd}}_{2}{\mathrm{Sn}}_{2}{\mathrm{O}}_{7}$. It undergoes a second order magnetic phase transition at ${T}_{c}\ensuremath{\approx}0.91$ K to a noncoplanar all-in--all-out magnetic structure of the ${\mathrm{Nd}}^{3+}$ magnetic moments. The thermal behavior of the low temperature specific heat fingerprints excitations with linear dispersion in a three-dimensional lattice. The temperature independent spin-lattice relaxation rate measured below ${T}_{c}$ and the anomalously slow paramagnetic spin dynamics detected up to $\ensuremath{\approx}30{T}_{c}$ are suggested to be due to magnetic short-range correlations in unidimensional spin clusters, i.e., spin loops. The observation of a spontaneous field in muon spin relaxation measurements is associated with the absence of a divergence-free field for the ground state of an all-in--all-out pyrochlore magnet as predicted recently.

We present the (x, T) phase diagram of the ferromagnetic Y2Co17−xCrx (x = 1.17, 1.76, 2.34, 3) compounds with rhombohedral structure (space group R 3 ¯ m , Th2Zn17-type), determined for the entire magnetically ordered regime from high-resolution neutron-diffraction data. Substitution of small amounts of Cr for Co was found to have drastic effects on the magnetic properties such as a decrease of the Curie (TC) and spin reorientation (TSR) temperatures as well as a decrease of the ordered-moment values. These effects could be brought into connection to the fact that Cr was found to have a preference for the four Co sites in the following order 6c > 18f > 9d > 18h. The number of Cr atoms found occupying the latter two sites, however, is within experimental error negligible. The magnetic phase diagram comprises three distinct regions of magnetic order in addition to the paramagnetic state: (a) the HT range (easy axis), (b) the LT (easy plane) for 0

The joint power of neutron diffraction and pressure techniques allows us to characterize under unique conditions th en ature and different role of basic interactions in solids. We have covere dab road phenomenology in archetypical compounds: intermetallics and magnetic oxides. We have selected compounds in which the effect of moderate pressure is able to modify the electronic structure and bond angles that in turn are in the bases of magnetic and structural transitions. Complex magnetic and structural phase diagrams are reported for compounds with magnetic (Tb1−X YX Mn2) and structural (RE5Si4−X GeX ) instabilities. Pressure-induced change of the magnetic structure in (R2Fe17) intermetallics and the effect on the colossal magnetoresistance manganites are described.

High-resolution neutron powder diffraction has been used to determine the crystal and magnetic structures of Ba2PrRuO6 and Ba2PrRu0.90Cu0.10O6. Both materials are 2116 distorted double perovskites and the magnetic structure, which develops below ∼110 K, consists of two interpenetrating Type I antiferromagnetic sublattices of the Ru5+ and Pr3+ ions. When saturated, the moments are ∼1.9 μB for Ru5+ and ∼1.1 μB for Pr3+ in the c-direction, though copper doping introduces an extra ab-component of ∼0.65 μB. From the study of variable temperature neutron diffraction data the principal magnetic interactions in the materials have been determined. Although an overall antiferromagnetic structure is adopted, the Ru–O–Pr ferromagnetic interaction is a factor of ∼4 times stronger than the Ru–O–O–Ru antiferromagnetic interaction.

Neutron powder diffraction has been used to study the two title compounds, Sr2HoRuO6 and Sr2TbRuO6, in order to determine the crystal and magnetic structures of the materials. Both materials have a distorted double perovskite structure and at temperatures below 30-40 K long-range magnetic order is observed. The. magnetic. structure for each compound consists of two interpenetrating Type I arrangements, one for the ruthenium sublattice and one for the rare earth sublattice, which are antiferromagnetically coupled to each other and order at the same temperature. From variable temperature measurements the combination of magnetic interactions and their relative strengths was deduced. The antiferromagnetic Ru-O-O-Ru interaction is approximately constant in the compounds, but it is a factor of 2.5 and 0.7 times stronger than the antiferromagnetic Ru-O-Ho and Ru-O-Tb interactions respectively.

The re-entrant magneto-elastic transition of the antiferromagnetic HoFe 4 Ge 2 compound has been studied by neutron powder diffraction as a function of temperature. The magnetic phase diagram comprises the wave vectors: ( q 1o , q 2o , q 1t ) and three magnetic transitions, two of them occurring simultaneously with the structural changes at T c , T N =52 and T c′ , T i c1 =15 K, the third being purely magnetic at T i c2 =40 K. The first transition is of second order while the latter two of first order . The sequence of phases follows the path: P4 2 /mnm (HT), T c , T N =52 K→ Cmmm (IT): ( q 1o =(0,1/2,0) , T i c 2 =40 K ⇒ q 2o =(0,q y ,0)) , T c′ , T i c 1 =15 K ⇒ P4 2 /mnm (LT): q 1t =(0,1/2,0) . The magnetic structures described by the wave vectors ( q 1o , q 2o and q 1t ), where the components are referred to the reciprocal basis of the conventional Cmmm cell, correspond to canted multi-axial arrangements. The q 2o wave vector length of the amplitude modulated phase varies non-monotonously, decreasing fast just below T i c2 ,—slowly between 36 K— T c′ , T i c1 and jumping to the q 1t =(0,1/2,0) lock-in value at T c′ , T i c1 simultaneously with the first order re-entrant transition to the (LT) tetragonal phase. In the coexisting meta-stable orthorhombic phase from T c′ , T i c1 down to 1.5 K the length of the wave vector q 2o continues to decrease. To solve the magnetic structures of all the phases appearing in this complex situation, arising from competing ordering mechanisms and anisotropies of the underlying sublattices, we have used the simulated annealing method of global optimisation on high-resolution neutron powder diffraction data.

The magnetic structure of Fe 2 Mo 3 O 12 was determined by neutron powder diffraction and magnetization studies. The magnetic unit cell is identical with the monoclinic chemical one ( Z =8), and the magnetic space group is P2 1 /a. The magnetic moments are ferromagnetically aligned along the b -axis for each sublattice corresponding to each Fe-site. There are four different Fe-sites, and the magnetic moments are parallel within two of them, but antiparallel to those of the other two sublattices, so that a ferrimagnetic structure results. The dominant antiferromagnetic supersuperexchange couplings are those along Fe–O–O–Fe paths with the two bridging oxygens belonging to one [MoO 4 ]-tetrahedron and forming large Fe–O–O and O–O–Fe angles.

The magnetic ordering of the tetragonal (I4/mmm) HoCo 2 X 2 (X=Ge, Si) and DyCo 2 Ge 2 compounds with the ThCr 2 Si 2 type of structure has been reinvestigated by neutron powder diffraction. The HoCo 2 Si 2 compound orders exclusively with the type-I antiferromagnetic structure with the wave vector q =(0, 0, 1) and the moments confined to the c -axis, while the magnetic phase diagrams of the DyCo 2 Ge 2 and HoCo 2 Ge 2 compounds comprise three distinct regions of magnetic ordering: a low-temperature structure also of type-I ( q 1 =(0, 0, 1)), stable in the range between 2 K and T IC , a high-temperature longitudinal sine wave modulated structure with the wave vector q 2 =(0 ,0, 1− q z ), stable in the range T IC – T N and a coexistence region of q 1 and q 2 around T IC . The wave vector component q z has a temperature-dependent length and locks-in by a first-order transition to the value q z =0 at T IC . In the case of the DyCo 2 Ge 2 compound a spin reorientation transition was detected in the low-temperature range. The ordered moment values at 1.5 K are 7.8(1) μ B /Dy and 9.33(1) μ B /Ho for the RCo 2 Ge 2 compounds and 8.8(1) μ B /Ho atom for the HoCo 2 Si 2 compound at 3 K.

A series of mixed ruthenium–copper oxides of general formulae A2YRu1−xCuxO6 with A = Sr, Ba and x = 0.05 to 0.15 were prepared by high temperature synthesis. Electrical and magnetic measurements confirmed the samples were superconducting. Variable temperature neutron powder diffraction studies were undertaken to determine the crystal and magnetic structures of the materials in the temperature range 2–100 K. Both series are double perovskites with the Sr compounds adopting a distorted structure with space group P21/n and the Ba materials in the cubic space group Fm3m. The neutron diffraction patterns clearly show the development of extra peaks at temperatures ∼30–40 K indicative of long-range magnetic order. Refinements of the data indicate that the Ru5+ ions adopt a Type I magnetic structure for both series with a magnetic moment at 2 K of ∼2.4(1) μB in the ab plane. The magnetic moment is found to increase slightly with increased copper doping in the Sr series, whereas the Ba series has a higher magnetic ordering temperature due to higher symmetry of the crystal structure.

The influence of hydrostatic pressure (up to 5 kbar) on the magnetic structure of Ce2Fe17 was investigated using neutron diffraction in the temperature range from 2 to 300 K. The existence of a collinear ferromagnetic phase below 95 K with a magnetic moment of Fe, mFe=2.0 μB, was confirmed at ambient pressure. Magnetic peaks present between 95 and 205 K correspond to an incommensurate antiferromagnetic structure with a wave vector changing its value from τ1=0.026 A−1 at 100 K to τ1=0.034 A−1 at 205 K. A helical model is used to describe the magnetic structure. Application of high pressures leads to significant changes of the magnetic structure. The ferromagnetic phase, suppressed in the studied temperature range by pressures higher than 3 kbar, gets substituted by a new incommensurate antiferromagnetic phase. This phase can be described as a superposition of the helical structure with a second antiferromagnetic coupling with propagation vector τ2≈0.078 A−1 at 40 K under pressures above 3 kbar. The correla...

The series of Sr 2 Fe 1− x Cr x MoO 6− y has been synthesized and studied by means of a wide set of experimental techniques. These samples belong to the family of A 2 BB′O 6 double perovskites with a ferrimagnetic ground state. The replacement of Fe by Cr leads to samples with a high oxygen deficiency and to increasing cation disorder between B and B′ sites. The magnetic moments of these samples decrease as the iron content does. Electrical properties change as well strongly along the series: while Sr 2 FeMoO 6 is metallic, the rest of the samples show a semiconducting behavior with an activation energy that increases as the content of Cr does. Only Fe-rich samples exhibit large negative magnetoresistance with the low-field response characteristic of a half-metallic system. The Cr-rich samples display instead a small linear negative magnetoresistance.

The influence of external pressure (P ⩽ 5 GPa) on both the structural and magnetic ordering in MnV2O4 has been investigated using neutron diffraction technique. The volume and the V-V distance decrease with pressure while the c/a ratio increases, suggesting a lowering of the distortion with pressure. Under ambient conditions this compound exhibits a structural transition (T S) from tetragonal to cubic at ~53 K and a magnetic transition (T N ) at ~56 K. It is found that with an increase in pressure to 5 GPa, T N increases (from 56 K to 80 K), dT N /dP > 0, while T S decreases (from 53 K to 37 K). The non collinear magnetic structure in the tetragonal phase at 5 GPa and 10 K remains the same as at ambient pressure. However, the Mn and V sublattice, now exhibits distinct transition temperatures, [Formula: see text] ~ 80 K, and [Formula: see text] ~ 60 K. The transition to the cubic phase at T S is accompanied by a collinear alignment of the Mn and V spins and a reduction in the Mn moment. The region in which the structure remains in the cubic phase with collinear magnetic structure increases with pressure from ~3 K at ambient pressure to ~43 K at 5 GPa pressure.

We report on the thermodynamic, magnetic properties and the magnetic structure of ludwigite-type Cu2MnBO5. The specific heat, the low-field magnetization and the paramagnetic susceptibility were studied on a single crystal and combined with powder neutron diffraction data. The temperature dependence of the specific heat and the neutron diffraction pattern reveal a single magnetic phase transition at T=92 K, which corresponds to the magnetic ordering into a ferromagnetic phase. The cation distribution and the values and directions of magnetic moments of ions in different crystallographic sites are established. The magnetic moments of Cu2+ and Mn3+ ions occupying different magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their directions do not coincide with the directions of the principal crystallographic axes.The small value of the magnetic moment of copper ions occupying site 2a is indicative of partial disordering of the magnetic moments on this site. The magnetization measurements show a strong temperature hysteresis of magnetization, which evidences for field-dependent transitions below the phase transition temperature., 15 pages, 10 figures

The synthesis of the new equiatomic RScSb (R = La-Nd, Sm, Gd-Tm, Lu, Y) compounds has been recently reported. These rare earth compounds crystallize in two different crystal structures, adopting the CeScSi-type (I4/mmm) for the lighter R (La-Nd, Sm) and the CeFeSi-type (P4/nmm) structure for the heavier R (R = Gd-Tm, Lu, Y). Here we report the results of neutron diffraction, magnetization and heat capacity measurements on some of these compounds (R = Ce, Pr, Nd, Gd and Tb). Band structure calculations have also been performed on CeScSb and GdScGe (CeScSi-type), and on GdScSb and TbScSb (CeFeSi-type) to compare and understand the exchange interactions in CeScSi and CeFeSi structure types. The neutron diffraction investigation shows that all five compounds order magnetically, with the highest transition temperature of 66 K in TbScSb and the lowest of about 9 K in CeScSb. The magnetic ground state is simple ferromagnetic (τ = [0 0 0]) in CeScSb, as well in NdScSb for 32 > T > 22 K. Below 22 K a second magnetic transition, with propagation vector τ = [¼ ¼ 0], appears in NdScSb. PrScSb has a magnetic structure within, determined by mostly ferromagnetic interactions and antiferromagnetic alignment of the Pr-sites connected through the I-centering (τ = [1 0 0]). A cycloidal spiral structure with a temperature dependent propagation vector τ = [δ δ ½] is found in TbScSb. The results of magnetization and heat capacity lend support to the main conclusions derived from neutron diffraction. As inferred from a sharp peak in magnetization, GdScSb orders antiferromagnetically at 56 K. First principles calculations show lateral shift of spin split bands towards lower energy from the Fermi level as the CeScSi-type structure changes to the CeFeSi-type structure. This rigid shift may force the system to transform from exchange split ferromagnetic state to the antiferromagnetic state in RScSb compounds (as seen for example in GdScSb and TbScSb) and is proposed to explain the change-over from a ferromagnetic structure as found in the CeScSi-type compounds CeScSb and NdScSb to the antiferromagnetic state as found in TbScSb and GdScSb.

Neutron scattering and AC susceptibility measurements have been made on isotopically enriched 154 SmMn 2 ( Ge 0.9 Si 0.1 ) 2 . A temperature versus pressure magnetic phase diagram is proposed. The incommensurate cone structures detected in SmMn2Ge2 at low temperatures and pressures do not appear in the phase diagram of the Si-substituted system. There is no evidence of a change in the magnetic structure associated with a small peak in susceptibility observed at around 145 K which has previously been interpreted in terms of changes to the cone structure. However, as with SmMn2Ge2, the non-collinear magnetic structures of these magnetic phases are such that a larger antiferromagnetic component appears within (0 0 1) ab -planes in the ferromagnetic states than in the antiferromagnetic state. With increasing Si substitution, the antiferromagnetic phase becomes the magnetic equilibrium state over a wider temperature range. The observed changes in the Mn–Mn spacing and magnetic coupling are largely consistent with previous related observations, although under a pressure of ∼8 kbar, low-temperature magnetic structures are found below the critical lattice spacing of a =4.031 A which are similar to those observed at ambient pressure.

The magnetic structures of TlCr5Se8 and Tl0.2Cr5Se8 were determined at 2 K using neutron scattering experiments. In the antiferromagnetic state the stoichiometric sample shows monoclinic symmetry with the magnetic cell exhibiting a doubling of the c-axis. All Cr atoms have magnetic moments in the b direction with magnitudes in accordance with Cr(III). As a consequence of direct and indirect superexchange, antiferromagnetic as well as ferromagnetic links between the different Cr atoms are observed. In Tl0.2Cr5Se8 in the antiferromagnetic state the symmetry is still monoclinic also showing a doubled c-axis. The Cr atoms have magnetic moments in the a–c-plane. Drastic changes of the Cr–Cr interatomic distances lead to a spin structure being significantly different from that observed for the stoichiometric sample. At about 70 K additional magnetic reflections which are due to the occurrence of an intermediate magnetic phase are observed in the powder pattern. The transition between the antiferromagnetic and the intermediate phase is accompanied by abrupt changes of the lattice parameters.

Variable-temperature powder neutron diffraction data demonstrate that FeV{sub 2}S{sub 4} undergoes a transition to a long-range magnetically ordered state at 135(7) K, in agreement with magnetic susceptibility data. High-resolution neutron diffraction data collected at 1.9 K reveal that magnetic ordering results in a doubling of the crystallographic unit-cell dimensions (I2/m a = 5.8303(2), b = 3.2761(1), c = 11.2398(4) {angstrom}, {beta} = 92.046(2){degree}) in the a and c directions and that the magnetic structure is described by a propagation vector of ({1/2}, 0, {1/2}). Cations in an ordered defect layer, 76% of which are Fe(II), possess an average ordered moment of 1.86(5) {mu}{sub B}, which is directed at an angle of 75{degree} to the layer. Cation-cation interactions reduce the average moment of cations in the MS{sub 2} unit to 0.17(4) {mu}{sub B}. The complex magnetic structure involves essentially collinear antiferromagnetic ordering between nearest-neighbor cations.

Powder neutron diffraction data for NixCr3−xS4(x= 1 4 , 1 2 , 3 4 ) collected over the temperature range 1.8≤T≤286 K demonstrate that all phases exhibit long-range magnetic order at low temperatures. The magnetic ordering temperature is composition dependent and increases with decreasing nickel content (205, 210, and 218 K forx= 3 4 , 1 2 , and 1 4 , respectively). The magnetic structure determined at 1.8 K involves a doubling of the unit cell in both theaand thecdirections. Moments associated with cations in a fully occupied metal layer, directed parallel to the cation layers, show little compositional dependence, whereas those associated with cations in an ordered vacancy layer are directed toward the anion layers and have a maximum value at the composition corresponding tox= 1 2 . At temperatures between 1.8 K and the ordering temperature, materials with compositions corresponding tox= 1 4 ; and 3 4 show a gradual 90° reorientation of the direction of the vacancy layer moments such that at temperatures just below the ordering temperature, moments lie parallel to the crystallographicb-axis.

The magnetic structure of the compounds Pr6Fe13Si and Nd6Fe13Au has been studied by powder neutron diffraction. The magnetic structures are very similar, revealing the same collinear antiferromagnetic ordering of the Fe (four) and the R (two) sublattices associated with the wavevector q = (001) and an IP type magnetic lattice with anticentring translation. The moments of all sublattices located in (xy0) layers and sandwiched between successive Si (Au) layers perpendicular to z at z = -0.25, 0.25, are confined to the same direction within the (xy0) plane. They change their direction collectively when going to the next Au (Si) layers at z = 0.25, 0.75, thus producing antiferromagnetic ordering within all eight sublattices. At 1.5 K, the rare earth moments in Nd6Fe13Au are equal to 3.4(2) µB for Nd1 and 2.5(1) µB for Nd2. In Pr6Fe13Si the two Pr sites have almost the same moment of 2.8(1) µB at 1.5 K. The average ordered Fe moment value is lower in Pr6Fe13Si (1.57 µB/Fe atom) than in Nd6Fe13Au (2.3 µB/Fe atom).

The magnetic phase diagram of the compound ErNiSi2 of CeNiSi2 structure type (Cmcm, space group) has been studied by neutron diffraction and magnetic measurements. The paramagnetic neutron data confirmed the sample homogeneity. The analysis of the data collected in the magnetically ordered regime (TN=3.4 K) showed the existence of two distinct types of magnetic ordering associated with the wave vectors q1=(1/2, 0, 0) and q2=(qx, qy, qz) which are not related by symmetry. The q1 phase corresponds to a uniaxial antiferromagnetic arrangement of the Er moments along b associated with a 2a cell enlargement. The refined moment value at 1.5 K is μEr=7.6(1) μB. This ordering is stable only below T1=1.8 K. Above T1, a first-order transition accompanied by hysteresis effects, leads to the appearance of a second set of magnetic reflections. These reflections are associated with a wave vector in a general reciprocal lattice position q2=(qx, qy, qz) that has a temperature dependent length and orientation. At T1 the two phases coexist and are present in equal amounts. The wave vector components of the q2 phase at T1 are qx=0.1262(3), qy=0.022(2) and qz=0.2273(3) r.l.u. The structure corresponds to a sine wave modulated structure with an amplitude of 5.31 μB polarized along b. This structure dominates the high-temperature region, T>T1. Below T1 it is still present as a metastable phase but its relative amount decreases with decreasing temperature. The same holds for the q1 phase which exists as a metastable phase above T1. The coexistence region on heating spans the interval T1±0.45 K.