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The interplay between a topological electronic structure and magnetism may result in intricate physics. In this work, we describe a case of rather peculiar coexistence or competition of several magnetic phases below seemingly single antiferromagnetic transition in

Monoclinic Li

The interplay between topological electronic structure and magnetism may result in intricate physics. In this work, we describe a case of rather peculiar coexistence or competition of several magnetic phases below a seemingly single antiferromagnetic transition in LnSbTe (Ln = Ho and Tb) topological semimetals, the magnetic members of the ZrSiS/PbFCl structure type (space group P4/nmm). Neutron diffraction experiments reveal a complex multi-step order below TN = 3.8 K (Ln = Ho) and TN = 6.4 K (Ln = Tb). Magnetic phases can be described using four propagation vectors: k1 = (1/2 0 0) and k2 = (1/2 0 1/4) at the base temperature of 1.7 K, which transform into incommensurate vectors k1' = (1/2 - d 0 0), k3 = (1/2 - d 0 1/2) at elevated temperatures in both compounds. Together with the refined models of magnetic structures, we present the group-theoretical analysis of the magnetic symmetry of the proposed solutions. These results prompt further investigations of the relation between the electronic structure of those semimetals and the determined antiferromagnetic ordering existing therein.

International audience; Solid electrolytes have regained tremendous interest recently in light of the exposed vulnerability of current rechargeable battery technologies. While designing solid electrolytes, most efforts concentrated on creating structural disorder (vacancies, interstitials, etc.) in a cationic Li/Na sublattice to increase ionic conductivity. In phosphates, the ionic conductivity can also be increased by rotational disorder in the anionic sublattice, via a paddle-wheel mechanism. Herein, we report on Na4Zn(PO4)(2) which is designed from Na3PO4, replacing Na+ with Zn2+ and introducing a vacancy for charge balance. We show that Na4Zn(PO4)(2) undergoes a series of structural transitions under temperature, which are associated with an increase in ionic conductivity by several orders of magnitude. Our detailed crystallographic study, combining electron, neutron, and X-ray powder diffraction, reveals that the room-temperature form, alpha-Na4Zn(PO4)(2), contains orientationally ordered PO4 groups, which undergo partial and full rotational disorder in the high-temperature beta- and gamma-polymorphs, respectively. We furthermore showed that the highly conducting gamma-polymorph could be stabilized at room temperature by ball-milling, whereas the beta-polymorph can be stabilized by partial substitution of Zn2+ with Ga2+ and Al3+. These findings emphasize the role of rotational disorder as an extra parameter to design new solid electrolytes.

LiFePO$_4$ (LFPO) is an archetypical and well-known cathode material for rechargeable Li-ion batteries. However, its quasi-one-dimensional (Q1D) structure along with the Fe ions, LFPO also displays interesting low-temperature magnetic properties. Our team has previously utilized the muon spin rotation ($\mu^+$SR) technique to investigate both magnetic spin order as well as Li-ion diffusion in LFPO. In this initial study we extend our investigation and make use of high-pressure $\mu^+$SR to investigate effects on the low-$T$ magnetic order. Contrary to theoretical predictions we find that the magnetic ordering temperature as well as the ordered magnetic moment increase at high pressure (compressive strain)., Comment: 8 pages, 6 figures, submitted as a part of the International Conference on Muon Spin Rotation, Relaxation and Resonance 2022. Accepted Dec 2022

Monoclinic Li$_3$Co$_2$SbO$_6$ has been proposed as a Kitaev spin liquid candidate and investigated intensively, whereas the properties of its polymorph, the orthorhombic phase, is less known. Here we report the magnetic properties of the orthorhombic Li$_3$Co$_2$SbO$_6$ as revealed by dc and ac magnetic susceptibility, muon spin relaxation ($\mu$SR) and neutron diffraction measurements. Successive magnetic transitions at (115, 89 and 71) K were observed in the low field dc susceptibility measurements. The transitions below $T_N$ (= 115 K), are suppressed in higher applied fields. However, zero field, ac susceptibility measurements reveals distinct frequency independent transitions at about (114, 107, 97, 79 and 71) K. A long range magnetic ordered state was confirmed by specific heat, $\mu$SR and neutron diffraction measurements, all indicating a single transition at about 115 K. The discrepancy between different measurements is attributed to possible stacking faults and/or local disorders of the ferromagnetic zig-zag chains, resulting in ferromagnetic boundaries within the overall antiferromagnetic matrix., Comment: 9 pages, 9 figures. Accepted by Inor. Chem

The antiferromagnetic structure of Tb

International audience; The high penetration ability of neutrons and dramatic character of crystal structure modifications occurring in battery materials during electrochemical cycling make neutron powder diffraction an obvious method to study the reaction mechanisms in rechargeable cells. Unfortunately, a typical balance of the available intensities of neutron beams and the amounts of active materials in commercial battery systems often limits the area of study to slow cycling rates or forces the use of too large amounts of materials, which in turn is incompatible with reliable electrochemistry. Herein we present a practical implementation of stroboscopic operando neutron diffraction to allow studying the structural changes occurring in a battery composed of a next generation 5 V disordered LiNi0.5Mn1.5O4 spinel cathode versus graphite during repetitive cycles at incredibly fast rates (up to 15C). We demonstrate that the graphite lithiation mechanisms at fast rates are different from those observed at reasonable rates. In particular, the earlier appearance and disappearance of lithiated graphite stages 1 and 2 in the charge and discharge processes, and also the suppression of the formation of the LiC18 phase can be associated with cell degradation at fast charge rates. This result is in agreement with the theoretical ‘shrinking-annuli’ model developed to simulate the electrochemical processes occurring during graphite lithiation at fast rates.

The magnetic ground states in highly ordered double perovskites LaSr1−xCaxNiReO6 (x = 0.0, 0.5, 1.0) are studied in view of the Goodenough-Kanamori rules of superexchange interactions in this paper. In LaSrNiReO6, Ni and Re sublattices are found to exhibit curious magnetic states separately, but no long range magnetic ordering is achieved. The magnetic transition at ~255 K is identified with the independent Re sublattice magnetic ordering. Interestingly, the sublattice interactions are tuned by modifying the Ni-O-Re bond angles through Ca doping. Upon Ca doping, the Ni and Re sublattices start to display a ferrimagnetically ordered state at low temperature. The neutron powder diffraction data reveals long range ferrimagnetic ordering of the Ni and Re magnetic sublattices along the crystallographic b-axis. The transition temperature of the ferrimagnetic phase increases monotonically with increasing Ca concentration.

We present a study of Cu-substitution effects in 4f-Ce intermetallic compound CeAu1-xCuxGe, with potentially unusual electronic states, in the whole concentration range (x = 0.0 - 1.0). The parent CeAuGe compound, crystallizing in a non-centrosymmetric hexagonal structure, is a ferromagnetic semimetal with Curie temperature 10 K. Cu-doping on Au-site of CeAuGe, CeAu1-xCuxGe, changes the crystal structure from the non-centrosymmetric (P63mc) to centrosymmetric (P63/mmc) space group at the concentration x ~ 0.5, where the c-lattice constant has a maximum value. Magnetic susceptibility and electrical resistivity measurements reveal that all Cu-doped compounds undergo magnetic phase transition near 10 K, with the maximum transition temperature of 12 K for x = 0.5. The neutron powder diffraction experiments show the ferromagnetic ordering of Ce3+ magnetic moments with a value of ~ 1.2 Bohr magneton at 1.8 K, oriented perpendicular to the hexagonal c-axis. By using symmetry analysis, we have found the solutions for the magnetic structure in the ferromagnetic Shubnikov space groups Cmc'21' and P21'/m' for x < 0.5 and x >= 0.5, respectively. Electrical resistivity exhibits a metallic temperature behaviour in all compounds. The resistivity has a local minimum in the paramagnetic state due to Kondo effects at high doping x = 0.8 and 1.0. At the small Cu-doping level, x = 0.2, the resistivity shows a broad feature at the ferromagnetic transition temperature and an additional transition-like peculiarity at 2.5 K in the ferromagnetic state., article including supplementary material

In this paper, we study the magnetic properties of orthorhombic (Pbnm) perovskites $\mathrm{Lu}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$ with $x=0.25$, 0.45, 0.55, and 0.75 by magnetization vs temperature and neutron powder diffraction measurements at room temperature. The magnetic moments are oriented along the $x$ direction with a G-type antiferromagnetic (AFM) arrangement that corresponds to irreducible representation ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${G}_{x}{A}_{y}{F}_{z}$). Magnetization reversal (MR) is observed for $0.45\ensuremath{\le}x\ensuremath{\le}0.75$. The MR phenomenon was modeled using Monte Carlo simulations, modeling both homogeneous and inhomogeneous cation distributions. For $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$, the presence of MR could only be explained using an inhomogeneous distribution with well-defined magnetic clusters. Looking at the staggered magnetization of each cluster, we propose a superparamagnetic regime of ${\mathrm{Fe}}^{3+}$ clusters in a ${\mathrm{Cr}}^{3+}$-rich matrix for $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$. By calculating the specific heat, we found that, in $\mathrm{Lu}{\mathrm{Fe}}_{0.45}{\mathrm{Cr}}_{0.55}{\mathrm{O}}_{3}$ and $\mathrm{Lu}{\mathrm{Fe}}_{0.25}{\mathrm{Cr}}_{0.75}{\mathrm{O}}_{3}$ the clusters order at nearly the same temperature ${T}_{N}^{\mathrm{Clus}}\ensuremath{\sim}535$ and 520 K, respectively, while the matrix orders at ${T}_{N}^{\mathrm{Mat}}\ensuremath{\sim}115\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. There is considerable reduction in the cluster ordering temperature as compared with the bulk, as ${T}_{N}\ensuremath{\sim}628\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{LuFe}{\mathrm{O}}_{3}$, while the matrix orders at the expected temperature as ${T}_{N}\ensuremath{\sim}115\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{LuCr}{\mathrm{O}}_{3}$.

The authors study a charge-orbital-spin correlation of high-pressure synthesized quasi-one-dimensional NaMn${}_{2}$O${}_{4}$ and Li${}_{0.92}$Mn${}_{2}$O${}_{4}$ using a low-temperature neutron powder diffraction.

We report on our evaluation of field-induced magnetic moments in the paramagnetic state of the $\text{spin-}\frac{1}{2}$ antiferromagnetic trimerized (${J}_{1}\ensuremath{-}{J}_{2}\ensuremath{-}{J}_{2}$) chain compound ${\mathrm{Cu}}_{3}{({\mathrm{P}}_{2}{\mathrm{O}}_{6}\mathrm{OD})}_{2}$ with ${J}_{1}=111\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${J}_{2}=30\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ [M. Hase et al., Phys. Rev. B 76, 064431 (2007)]. Magnetic reflections with integer indices, generated by field-induced magnetic moments, were observed at neutron-diffraction experiments performed in an applied magnetic field, and we evaluated the magnitudes of the moments to be ${M}_{1}=0.43(2)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Cu}$ and ${M}_{2}=0.013(10)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Cu}$ on the two crystallographic ${\mathrm{Cu}}^{2+}$ (Cu1 and Cu2) sites, respectively, at 6 T and 1.6 K. The resulting ratio ${M}_{2}/{M}_{1}=0.03(2)$ is in good agreement with the theoretical value for the ratio of the magnetization at the two sites. We thus conclude that for this well-understood spin system (which has the advantage of being amenable to detailed theoretical calculations) the extracted field-induced magnetic moments reproduce the correct information on the magnetization. Our result leads us to believe that we can precisely evaluate exchange interactions in paramagnets with multiple exchange interactions and multiple crystallographic magnetic-ion sites by using field-induced magnetic moments in combination with macroscopic physical quantities. This idea is expected to be applicable to a wide variety of quantum and frustrated magnets without long-range order.

Spin liquids are highly correlated yet disordered states formed by the entanglement of magnetic dipoles$^1$. Theories typically define such states using gauge fields and deconfined quasiparticle excitations that emerge from a simple rule governing the local ground state of a frustrated magnet. For example, the '2-in-2-out' ice rule for dipole moments on a tetrahedron can lead to a quantum spin ice in rare-earth pyrochlores - a state described by a lattice gauge theory of quantum electrodynamics$^{2-4}$. However, f-electron ions often carry multipole degrees of freedom of higher rank than dipoles, leading to intriguing behaviours and 'hidden' orders$^{5-6}$. Here we show that the correlated ground state of a Ce$^{3+}$-based pyrochlore, Ce$_2$Sn$_2$O$_7$, is a quantum liquid of magnetic octupoles. Our neutron scattering results are consistent with the formation of a fluid-like state of matter, but the intensity distribution is weighted to larger scattering vectors, which indicates that the correlated degrees of freedom have a more complex magnetization density than that typical of magnetic dipoles in a spin liquid. The temperature evolution of the bulk properties in the correlated regime below 1 Kelvin is well reproduced using a model of dipole-octupole doublets on a pyrochlore lattice$^{7-8}$. The nature and strength of the octupole-octupole couplings, together with the existence of a continuum of excitations attributed to spinons, provides further evidence for a quantum ice of octupoles governed by a '2-plus-2-minus' rule. Our work identifies Ce$_2$Sn$_2$O$_7$ as a unique example of a material where frustrated multipoles form a 'hidden' topological order, thus generalizing observations on quantum spin liquids to multipolar phases that can support novel types of emergent fields and excitations.

Solid electrolytes have regained tremendous interest recently in light of the exposed vulnerability of current rechargeable battery technologies. While designing solid electrolytes, most efforts concentrated on creating structural disorder (vacancies, interstitials, etc.) in a cationic Li/Na sublattice to increase ionic conductivity. In phosphates, the ionic conductivity can also be increased by rotational disorder in the anionic sublattice, via a paddle-wheel mechanism. Herein, we report on Na

We have investigated the magnetic ground state of a novel one-dimensional compound, NaCr 2 O 4 , in which Cr 2 O 4 double chains, i.e. zig-zag chains are aligned parallel to the b -axis, by means of both muon-spin rotation and relaxation ( μ + SR) and neutron diffraction (ND) measurements. The μ + SR results reveal the formation of static antiferromagnetic order below Neel temperature ( T N = 124 K ). The ND measurements also demonstrate the appearance of magnetic Bragg peaks with the propagation vector k → = ( 1, 0, 1 ) below T N . Combined analyses of the μ + SR and ND data clarify that the Cr moments in each zig-zag chain are aligned ferromagnetically along the c -axis, whereas antiferromagnetically along the a -axis between the adjacent zig-zag chains.

(Lu1–xMnx)MnO3 solid solutions, having the perovskite-type structure and Pnma space group, with 0 ≤ x ≤ 0.4 were synthesized by a high-pressure, high-temperature method at 6 GPa and about 1670 K fr...

Ionic conductivity in a compound is rooted in a delicate interplay between its crystal structure and its structural defects (vacancies, interstitials, etc.). Hence, understanding this interplay is of utmost importance to design new solid state electrolytes. To shed some light on the above query, we investigated the rich crystal chemistry of Li6Zn(P2O7)2. This compound undergoes multiple structural transitions under the influence of temperature, which increases the conductivity by several orders and lowers the activation energy. We explained this jump in conductivity by the increased disorder associated with cation mixing. Our structural exploration indicates that both the room-temperature α-polymorph and the high-temperature ζ-polymorph crystallize in a C2/c space group but with a much smaller unit cell volume for the latter. While their structural framework based on P2O74– is similar, the ζ-polymorph presents a fully disordered Li/Zn sublattice, while it is fully ordered for the α-polymorph. Furthermore,...

Angle-resolved photoelectron spectroscopy has been used to follow the valence band and near Fermi edge electronic band structure in the quasi-1D compound NaV 2 O 4 . In this current study we have acquired the very first high-quality, high-resolution ARPES data from this material. Our data clearly reveal two distinct dispersive bands that cross the Fermi level at different k F . This is a clear signature that the electronic properties of this material is affected by the presence of a mixed valence state on the different vanadium chains and possibly also the low-temperature magnetic spin order.

The hydrogenation properties of the intermetallic compounds MgPd2 and Pd2Zn, crystallizing in the Co2Si type, were studied by in situ thermal analysis (DSC) under hydrogen pressure. Pd2Zn does not show any reaction with hydrogen while MgPd2 reversibly forms the hydride MgPd2H. Neutron diffraction on the deuterides reveals the compositions MgPd2D0.861(6) (ambient) and MgPd2D0.97(1) [308(2) K, 2.56(5) MPa deuterium] with hydrogen (deuterium) occupying distorted [MgPd5] octahedral voids. Quantum mechanical calculations support the structure models and show the hydrogenation to be exergonic for MgPd2 and endergonic for Pd2Zn. MgPd2H releases hydrogen under normal conditions or vacuum. Heating under hydrogen pressure leads first reversibly to MgPd2H≈0.2 and subsequently irreversibly to MgPd3H≈1 and MgH2. MgPd2, Pd2Zn, and MgPd2H were classified in a structure map. Trends of axial ratio changes upon hydrogenation of TiNiSi type and ZrBeSi type compounds are discussed.

International audience; We report on a thorough structural study on two members of layered fluorocarbonates KMCO3F (M = Ca, Mn). The Ca-based member demonstrates a phase transition at similar to 320 degrees C, evidenced for the first time. The crystal structure of the high temperature phase (HT-KCaCO3F) was solved using neutron powder diffraction. A new Mn-based phase KMnCO3F was synthesized, and its crystal structure was solved from electron diffraction tomography data and refined from a combination of X-ray synchrotron and neutron powder diffraction. In contrast to other members of the fluorocarbonate family, the carbonate groups in the KMnCO3F and HT-KCaCO3F structures are not fixed to two distinct orientations corresponding to mono- and bidentate coordinations of the M cation. In KMnCO3F, the carbonate group can be considered as nearly "monodentate", forming one short (2.14 angstrom) and one long (3.01 angstrom) MnO contact. This topology provides more flexibility to the MCO3 layer and enables diminishing the mismatch between the MCO3 and KF layers. This conclusion is corroborated by the HT-KCaCO3F structure, in which the carbonate groups can additionally be tilted away from the layer plane thus relieving the strain arising from geometrical mismatch between the layers. The correlation between denticity of the carbonate groups, their mobility, and cation size variance is discussed. KMnCO3 orders antiferromagnetically below T-N = 40 K.

A detailed neutron scattering study of the Shastry–Sutherland material SrCu2(BO3)2 verifies the existence of a 4-spin plaquette singlet phase in this system.

We investigate the magnetic structure and the electric properties of $\mathrm{YC}{\mathrm{r}}_{0.5}\mathrm{F}{\mathrm{e}}_{0.5}{\mathrm{O}}_{3}$, which was earlier reported to feature ferroelectricity from nonequivalent spins due to the cation disorder. We find a centrosymmetric magnetic order at all temperatures below ${T}_{N}$, which is incompatible with magnetically induced ferroelectricity. Our dielectric and pyroelectric studies also do not support intrinsic ferroelectricity in this system.

A high-pressure synthesis method was employed to prepare Mn-self-doped perovskites (R 0.667Mn0.333)MnO3 (R = Yb, Lu) at about 6 GPa and 1670 K. Crystal and magnetic structures of (Yb0.667Mn0.333)MnO3 have been studied by combining neutron powder diffraction, magnetic susceptibility and specific heat measurements. Within the orthorhombic space group Pnma, magnetic cations are located on site 4c (A site, occupied by two thirds of Yb3+ and one third of Mn2+) and on site 4b (B site, occupied by two thirds of Mn3+ and one third of Mn4+). The degree of structural distortion of the MnO6 octahedra follows the general trend of (R1−x Mn x )MnO3 compounds which shows a decrease with increasing amount of Jahn–Teller inactive Mn4+ cations. Mn–Mn interactions produce a collinear ferrimagnetic structure (T C,Mn = 106 K) with ferromagnetically ordered Mn moments at the B site being coupled antiferromagnetically with ordered Mn moments at the A site. Mn–Yb interactions induce a small but non-zero ferromagnetic Yb3+ moment which can explain a small decrease of the magnetic susceptibility at low temperature. Yb–Yb interactions create an antiferromagnetic structure at T N,Yb ≈ 40 K. Ordered moments of the ferrimagnetic and antiferromagnetic structures are oriented perpendicular to each other within the ac-plane and Yb3+ moments contribute to both structures. The appearance of ordered Yb3+ moments induced by Mn–Yb interactions in perovskite (Yb0.667Mn0.333)MnO3 is a result of the Mn self-doping on the A site and has not been observed in the orthorhombic perovskite modification (space group Pnma) of the undoped parent compound YbMnO3, but interestingly, it also appears in the hexagonal non-perovskite modification (space group P63 cm) of YbMnO3.

A high-pressure synthesis method was employed to prepare (Ho1-xMnx)MnO3 solid solutions with x = 0.2 and 0.3 (at about 6 GPa and 1,670 K) and magnetic properties and structures were investigated by magnetic, dielectric and neutron diffraction measurements. Both samples crystallize in the GdFeO3-type Pnma perovskite structure, and both samples show magnetization reversal behavior below the compensation temperature of about 35 K (at H = 100 Oe). The magnetization reversal phenomena are originated from a ferrimagnetic (FiM) structure which takes place below TC = 76 K (x = 0.2) and 102 K (x = 0.3) and is built from ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site which are antiferromagnetically (AFM) coupled with Ho3+ and Mn2+ cations at the A site. The magnetic moment of Ho3+ cations increases significantly with deceasing temperature, and it overcomes the saturated magnetic moment of Mn3+ and Mn4+ cations at the B site. Field-induced first-order transitions were found in both compounds below about 35 K. Neutron diffraction measurements on the x = 0.2 sample found a collinear FiM structure between 76 K and 40 K, and the development of spin canting at the A site below 40 K. The coexistence of Ho3+ and Mn2+ at the A-site gives rise to additional short-range magnetic ordering of Ho3+ and to strain effects along the a-direction which are stronger than in (R1−xMnx)MnO3 materials with heavier and smaller rare-earths cations.

Cationic rearrangement is a compelling strategy for producing desirable physical properties by atomic-scale manipulation. However, activating ionic diffusion typically requires high temperature, and in some cases also high pressure in bulk oxide materials. Herein, we present the cationic rearrangement in bulk Mn2 FeMoO6 at unparalleled low temperatures of 150-300 (o) C. The irreversible ionic motion at ambient pressure, as evidenced by real-time powder synchrotron X-ray and neutron diffraction, and second harmonic generation, leads to a transition from a Ni3 TeO6 -type to an ordered-ilmenite structure, and dramatic changes of the electrical and magnetic properties. This work demonstrates a remarkable cationic rearrangement, with corresponding large changes in the physical properties in a bulk oxide at unprecedented low temperatures.

Quantum materials that feature magnetic long-range order often reveal complex phase diagrams when localized electrons become mobile. In many materials magnetism is rapidly suppressed as electronic charges dissolve into the conduction band. In materials where magnetism persists, it is unclear how the magnetic properties are affected. Here we study the evolution of the magnetic structure in Nd_{1-x}Ce_{x}CoIn_{5} from the localized to the highly itinerant limit. We observe two magnetic ground states inside a heavy-fermion phase that are detached from unconventional superconductivity. The presence of two different magnetic phases provides evidence that increasing charge delocalization affects the magnetic interactions via anisotropic band hybridization.

The compounds ${A}_{2}\mathrm{C}{\mathrm{u}}_{3}\mathrm{O}{(\mathrm{S}{\mathrm{O}}_{4})}_{3}\phantom{\rule{0.28em}{0ex}}(A=\mathrm{Na},\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ are characterized by copper hexamers which are weakly coupled along the $b$ axis to realize one-dimensional antiferromagnetic chains below ${T}_{\mathrm{N}}\ensuremath{\approx}3\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, whereas the interchain interactions along the $a$ and $c$ axes are negligible. We investigated the energy-level splittings of the copper hexamers by inelastic neutron scattering below and above ${T}_{\mathrm{N}}$. The eight lowest-lying hexamer states could be unambiguously assigned and parametrized in terms of a Heisenberg exchange Hamiltonian, providing direct experimental evidence for an $S=1$ triplet ground-state associated with the copper hexamers. Therefore, the compounds ${A}_{2}\mathrm{C}{\mathrm{u}}_{3}\mathrm{O}{(\mathrm{S}{\mathrm{O}}_{4})}_{3}$ serve as cluster-based spin-1 antiferromagnets to support Haldane's conjecture that a gap appears in the excitation spectrum below ${T}_{\mathrm{N}}$, which was verified by inelastic neutron scattering.

The compounds ${\mathrm{BaDy}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{BaHo}}_{2}{\mathrm{O}}_{4}$ are part of a family of frustrated systems exhibiting interesting properties, including spin-liquid-type ground states, magnetic-field-induced phases, and the coexistence of short- and long-range magnetic order, with dominant one-dimensional correlations, which can be described as Ising ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ zigzag chains along the $c$ axis. We have investigated polycrystalline samples of ${\mathrm{BaDy}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{BaHo}}_{2}{\mathrm{O}}_{4}$ with both neutron diffraction and neutron spectroscopy, coupled to detailed crystalline electric field calculations. The latter points to site-dependent anisotropic magnetism in both materials, which is corroborated by the magnetic structures we determined. The two systems show the coexistence of two different long-range orders: two double N\'eel $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$ orders in the $ab$ plane with propagation vectors ${\mathbf{k}}_{1}=(\frac{1}{2},0,\frac{1}{2})$ and ${\mathbf{k}}_{2}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ for ${\mathrm{BaDy}}_{2}{\mathrm{O}}_{4}$, and two distinct arrangements of simple N\'eel $\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\uparrow}\ensuremath{\downarrow}$ orders along the $c$ axis, both with the propagation vector ${\mathbf{k}}_{0}=(0,0,0)$ for ${\mathrm{BaHo}}_{2}{\mathrm{O}}_{4}$. The order for both wave vectors in ${\mathrm{BaDy}}_{2}{\mathrm{O}}_{4}$ occurs at ${T}_{\mathrm{N}}=0.48\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, while in ${\mathrm{BaHo}}_{2}{\mathrm{O}}_{4}$ the first order sets in at ${T}_{\mathrm{N}}\ensuremath{\sim}\phantom{\rule{3.33333pt}{0ex}}1.3\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and the second one has a lower ordering temperature of 0.84 K. Both compounds show extensive diffuse scattering which we successfully modeled with a one-dimensional axial next-nearest neighbor Ising (ANNNI) model. In both materials, strong diffusive scattering persists to temperatures well below where the magnetic order is fully saturated.

In this work we present the magnetic structures and spin reorientation (SR) transitions of the mixed orthochromite-orthoferrite perovskites $R\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ ($R=\mathrm{Tb}$, Dy, Ho, Er). Magnetization as a function of temperature and external magnetic field as well as neutron powder diffraction measurements were used to characterize the magnetic transitions, including the SR transitions in the transition metal sublattice and the ordering of the rare earth sublattice. The studied compounds order antiferromagnetically below 270 K in a ${\mathbf{G}}_{\mathbf{x}}$ configuration compatible with the ${\mathrm{\ensuremath{\Gamma}}}_{4}$ representation. As temperature decreases, all the compounds show a SR transition from ${\mathbf{G}}_{\mathbf{x}}$ (${\mathrm{\ensuremath{\Gamma}}}_{4}$) to ${\mathbf{G}}_{\mathbf{z}}$ (${\mathrm{\ensuremath{\Gamma}}}_{2}$). This transition occurs in a wide temperature range, where both magnetic configurations coexist. Below this SR, the behavior in each case depends on the rare earth. $\mathrm{HoF}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ shows $\mathrm{H}{\mathrm{o}}^{3+}$ sublattice ordering at a relatively high temperature (45 K). $\mathrm{DyF}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ and $\mathrm{ErF}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ show a second SR transition of the transition metal sublattice, from ${\mathbf{G}}_{\mathbf{z}}$ (${\mathrm{\ensuremath{\Gamma}}}_{2}$) to ${\mathbf{G}}_{\mathbf{y}}$ (${\mathrm{\ensuremath{\Gamma}}}_{1}$) at low temperatures (15 and 8 K, respectively). Below these temperatures a metamagnetic (MM) transition is observed for these two compounds at an external magnetic field of H \ensuremath{\approx} 7 kOe. The fact that this is only observed for compounds showing ${\mathbf{G}}_{\mathbf{z}}$ (${\mathrm{\ensuremath{\Gamma}}}_{2}$) to ${\mathbf{G}}_{\mathbf{y}}$ (${\mathrm{\ensuremath{\Gamma}}}_{1}$) transition suggests that there is a correlation between the ${\mathbf{G}}_{\mathbf{y}}$ (${\mathrm{\ensuremath{\Gamma}}}_{1}$) order and the MM transition. Finally, $\mathrm{TbF}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ is a peculiar case, since it is the only compound in this family that shows a re-entrant SR to ${\mathbf{G}}_{\mathbf{x}}$ (${\mathrm{\ensuremath{\Gamma}}}_{4}$) at very low temperatures. By combining these results with previous reports on $R\mathrm{Fe}{\mathrm{O}}_{3}$, $R\mathrm{Cr}{\mathrm{O}}_{3}$, and $R\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$, we develop a method to qualitatively estimate the SR temperature and the type of transition. We also propose a complete magnetic phase diagram containing the SR transitions and ${R}^{3+}$ ordering temperatures for all the $R\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ ($R=\mathrm{Tb}$, Dy, Ho, Er, Tm, Yb, and Lu) compounds.

We present a detailed study of the thermal dependence of the neutron powder diffraction (NPD) of $R\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{o}}_{0.5}{\mathrm{O}}_{3}$ perovskites ($R=\mathrm{Tm}$, Er, Ho, Dy, and Tb) combined with a complete characterization of their magnetic, electric transport and ferroelectric properties. All samples are described with an orthorhombic (Pbnm) crystallographic structure. The inverse of magnetic susceptibility at high temperature shows an effective magnetic moment with contributions of high-spin $\mathrm{C}{\mathrm{o}}^{3+}$, $\mathrm{F}{\mathrm{e}}^{3+}$, and the corresponding rare-earth cations (${R}^{3+}$) moments. Negative Curie-Weiss temperatures indicate antiferromagnetic (AFM) correlations between the magnetic ions. At low temperature, the reduced magnetic saturation values are associated with crystal-field effects on ${R}^{3+}$ ions. Below 300 K, magnetic reflections in NPD data show that the spin configuration in the ordered state is AFM type-G with a weak ferromagnetic component along the $c$ axis (${\mathrm{\ensuremath{\Gamma}}}_{4}$) for transition metal ions. Spin reorientation (SR) transitions are observed, changing the irreducible representation from ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${G}_{x}$) to ${\mathrm{\ensuremath{\Gamma}}}_{2}({G}_{z})$ at low temperatures, except for the Ho compound where it changes from ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${G}_{x}$) to ${\mathrm{\ensuremath{\Gamma}}}_{1}({G}_{y})$. Magnetization data under field cooling (FC) and zero field cooling (ZFC) protocols show reversal magnetization for $R=\mathrm{Er}$ and Tb. A significant change of the slope of the M vs T curves is associated with the onset of magnetic order (${T}_{N1}\ensuremath{\sim}250\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) of Fe/Co sublattice. The electric conductivity at room temperature shows that Tm value is ten times less than the other rare earths. The temperature dependence of the electrical conductivity can be described with a variable range hopping model ($\mathrm{ln}\ensuremath{\sigma}\ensuremath{\sim}{T}^{\ensuremath{-}1/4}$). Also, in the Tm case, the complex electrical permittivity shows a different behavior in comparison with the other members of the series. Finally, the Tm sample can be polarized when the specimen is cooled under different values of electrical field (E). Pyroelectric current can be detected while the sample is warming and depolarized, showing the ferroelectric critical temperature (${T}_{C}$) at ${T}_{N1}$. A low electric polarization of $400\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ was measured for $\mathrm{TmF}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{o}}_{0.5}{\mathrm{O}}_{3}$.

Ionic conductivity in a compound is rooted in a delicate interplay between its crystal structure and its structural defects (vacancies, interstitials, etc.). Hence, understanding this interplay is of utmost importance to design new solid state electrolytes. To shed some light on the above query, we investigated the rich crystal chemistry of Li

The magnetic ordering of ${\mathrm{La}}_{1/3}{\mathrm{Sr}}_{2/3}{\mathrm{FeO}}_{3}$ perovskite has been studied by neutron powder diffraction and $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy down to 2 K. From symmetry analysis, a chiral helical model and a collinear model are proposed to describe the magnetic structure. Both are commensurate, with propagation vector $\mathbf{k}=(0,0,1)$ in $R\overline{3}c$ space group. In the former model, the magnetic moments of Fe adopt the magnetic space group $P{3}_{2}21$ and have helical and antiferromagnetic ordering propagating along the $c$ axis. The model allows only a single Fe site, with a magnetic moment of 3.46(2)${\ensuremath{\mu}}_{\mathrm{B}}$ at 2 K. In the latter model, the magnetic moments of iron ions adopt the magnetic space group $C2/c$ or $C{2}^{\ensuremath{'}}/{c}^{\ensuremath{'}}$ and are aligned collinearly. The model allows the presence of two inequivalent Fe sites with magnetic moments of amplitude 3.26(3)${\ensuremath{\mu}}_{\mathrm{B}}$ and 3.67(2)${\ensuremath{\mu}}_{\mathrm{B}}$, respectively. The neutron-diffraction pattern is equally well fitted by either model. The M\"ossbauer spectroscopy study suggests a single charge state ${\mathrm{Fe}}^{3.66+}$ above the magnetic transition and a charge disproportionation into ${\mathrm{Fe}}^{(3.66\ensuremath{-}\ensuremath{\zeta})+}$ and ${\mathrm{Fe}}^{(3.66+2\ensuremath{\zeta})+}$ below the magnetic transition. The compatibility of the magnetic structure models with the M\"ossbauer spectroscopy results is discussed.

We present an experimental study for polycrystalline samples of the diluted magnetic semiconductor MnxGa1−xN (x 0.04) in order to address some of the existing controversial issues. X-ray and neutron diffraction, x-ray absorption near-edge structure, and electron paramagnetic resonance experiments were used to characterize the structural, electronic, and magnetic properties of the samples, and inelastic neutron scattering was employed to determine the magnetic excitations associated with Mn monomers and dimers. Our main conclusions are as follows: (i) The valence of the Mn ions is 2+. (ii) The Mn2+ ions experience a substantial single-ion axial anisotropy with parameter D = 0.027(3) meV. (iii) Nearest-neighbor Mn2+ ions are coupled antiferromagnetically. The exchange parameter J = −0.140(7) meV is independent of the Mn content x; i.e., there is no evidence for hole-induced modifications of J towards a potentially high Curie temperature postulated in the literature.

Polycrystalline samples of Fe3−yGeTe2(0.08 ≤y≤ 0.29) and the solid solutions Fe3−x−yNixGeTe2(0.24 ≤x≤ 1.32; 0.14 ≤y≤ 0.41) were synthesized at 898–973 K in a resistance furnace and characterized by X-ray and neutron powder diffraction with Rietveld analysis (Fe3GeTe2type,P63/mmc,a= 402.665(3),c= 1632.820(14) pm forx= 0,y= 0.08). Fe3Ge layers with planar FeGe hexagons and additional iron atoms above and below the rings are separated by double layers of tellurium atoms. Fe3GeTe2is ferromagnetic belowTC= 230 K with magnetic moments aligned along thecaxis.TCdepends on the iron content and decreases with increasing iron vacancies continuously to 153 K in Fe2.71GeTe2. Further reduction ofTCis possible by nickel substitution until magnetic ordering is nearly absent in Fe1.33Ni1.32GeTe2. The suppression of the magnetic ordering is caused by random dilution of the magnetic iron atoms either by vacancies or by non-magnetic nickel atoms.

We describe the preparation, crystal structure determination and magnetic properties of a new series of ordered double perovskite oxides Sr2LnMoO6 (Ln = Eu, Gd, Dy, Ho, Er, Yb) with Mo5+ and Ln3+ electronic configurations. These compounds have been obtained by solid state reaction under reducing conditions in order to stabilize Mo5+ cations. Structural characterization by XRPD and NPD was performed when Ln = Ho, Er, Yb and just XRPD for absorbing Ln = Eu, Gd, Dy. At room temperature, an excellent Rietveld fit was obtained for all the samples in a monoclinic symmetry, space group P21/n, with long-range ordering of Ln and Mo atoms. Magnetic susceptibility measurements show that some of these materials present magnetic ordering below 25 K and the determined effective magnetic moments are consistent with those expected for the pair Ln3+-Mo5+. All the phases have negative dominance of the Weiss temperature indicating dominance of antiferromagnetic interactions., S.A.L. and C.A.L. thank CONICET fellowships. J.C.P. and RDS thanks the CONICET (Projects PIP 01360/08, PIP 00912/12 and PIP 00450/11) and SECyT-UNSL (Projects PROICO 7707 and PROICO 2-1612). J.C.P. and R.D.S are members of CONICET. J.A.A. acknowledges the financial support of the Spanish Ministry of Science and Innovation to the project MAT2010-16404.

The magnetic nature of a novel one-dimensional compound NaCr 2 O 4 with zigzag CrO 2 chains has been studied by muon spin rotation and relaxation ( μ +SR) and neutron diffraction (ND). It is found that NaCr 2 O 4 undergoes an antiferromagnetic transition at T N = 125 K, below which the Cr moments in each zigzag chain align ferromagnetically along the c -axis but antiferromagnetically along the a -axis between adjacent zigzag chains. For the solid solution system Ca 1-x Na x Cr 2 O 4 , μ + SR measurements reveal the evolution of a complex magnetic order with increasing Ca content (1- x ), which finally enters into an incommensurate AF ordered state below T N = 21 for CaCr 2 O 4 .

We report an extensive study on the zero field ground state of a powder sample of the pyrochlore ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$. A sharp heat capacity anomaly that labels a low temperature phase transition in this material is observed at 280 mK. Neutron diffraction shows that a quasicollinear ferromagnetic order develops below ${T}_{\mathrm{c}}$ with a magnetic moment of $0.87(2){\ensuremath{\mu}}_{\mathrm{B}}$. High resolution inelastic neutron scattering measurements show, below the phase transition temperature, sharp gapped low-lying magnetic excitations coexisting with a remnant quasielastic contribution likely associated with persistent spin fluctuations. Moreover, a broad inelastic continuum of excitations at $\ensuremath{\sim}0.6$ meV is observed from the lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has vanished and a broad quasielastic conventional paramagnetic scattering takes place at the observed energy range. Finally, we show that the exchange parameters obtained within the framework of linear spin-wave theory do not accurately describe the observed zero field inelastic neutron scattering data.

The charge ordered structure of ions and vacancies characterizing rare-earth pyrochlore oxides serves as a model for the study of geometrically frustrated magnetism. The organization of magnetic ions into networks of corner-sharing tetrahedra gives rise to highly correlated magnetic phases with strong fluctuations, including spin liquids and spin ices. It is an open question how these ground states governed by local rules are affected by disorder. In the pyrochlore Tb$_2$Hf$_2$O$_7$, we demonstrate that the vicinity of the disordering transition towards a defective fluorite structure translates into a tunable density of anion Frenkel disorder while cations remain ordered. Quenched random crystal fields and disordered exchange interactions can therefore be introduced into otherwise perfect pyrochlore lattices of magnetic ions. We show that disorder can play a crucial role in preventing long-range magnetic order at low temperatures, and instead induces a strongly-fluctuating Coulomb spin liquid with defect-induced frozen magnetic degrees of freedom., 18 pages, 4 figures, + Supplementary Information (4 figures)

We report on a thorough structural study on two members of layered fluorocarbonates KMCO

Magnetic frustration and low dimensionality can prevent long range magnetic order and lead to exotic correlated ground states. SrDy$_2$O$_4$ consists of magnetic Dy$^{3+}$ ions forming magnetically frustrated zig-zag chains along the c-axis and shows no long range order to temperatures as low as $T=60$ mK. We carried out neutron scattering and AC magnetic susceptibility measurements using powder and single crystals of SrDy$_2$O$_4$. Diffuse neutron scattering indicates strong one-dimensional (1D) magnetic correlations along the chain direction that can be qualitatively accounted for by the axial next-nearest neighbour Ising (ANNNI) model with nearest-neighbor and next-nearest-neighbor exchange $J_1=0.3$ meV and $J_2=0.2$ meV, respectively. Three-dimensional (3D) correlations become important below $T^*\approx0.7$ K. At $T=60$ mK, the short range correlations are characterized by a putative propagation vector $\textbf{k}_{1/2}=(0,\frac{1}{2},\frac{1}{2})$. We argue that the absence of long range order arises from the presence of slowly decaying 1D domain walls that are trapped due to 3D correlations. This stabilizes a low-temperature phase without long range magnetic order, but with well-ordered chain segments separated by slowly-moving domain walls.

Strontium doping transforms manganites of type La(1-x)Sr(x)MnO(3) from an insulating antiferromagnet (x=0) to a metallic ferromagnet (x>0.16) due to the induced charge carriers (holes). Neutron scattering experiments were employed to investigate the effect of Sr doping on a tailor-made compound of composition La(0.7)Sr(0.3)Mn(0.1)Ti(0.3)Ga(0.6)O(3). By the simultaneous doping with Sr2+ and Ti4+ ions the compound remains in the insulating state, so that the magnetic interactions for large Sr doping can be studied in the absence of charge carriers. At TC=215 K there is a first-order reconstructive phase transition from the trigonal R-3c structure to the orthorhombic Pnma structure via an intermediate virtual configuration described by the common monoclinic subgroup P21/c. The magnetic excitations associated with Mn3+ dimers give evidence for two different nearest-neighbor ferromagnetic exchange interactions, in contrast to the undoped compound LaMnyA(1-y)O(3) where both ferromagnetic and antiferromagnetic interactions are present. The doping induced changes of the exchange coupling originates from different Mn-O-Mn bond angles determined by neutron diffraction. The large fourth-nearest-neighbor interaction found for metallic manganites is absent in the insulating state. We argue that the Ruderman-Kittel-Kasuya-Yosida interaction reasonably accounts for all the exchange couplings derived from the spin-wave dispersion in metallic manganites.