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Competition among exchange interactions is able to induce novel spin correlations on a bipartite lattice without geometrical frustration. A prototype example is the spiral spin liquid, which is a correlated paramagnetic state characterized by sub-dimensional degenerate propagation vectors. Here, using spectral graph theory, we show that spiral spin liquids on a bipartite lattice can be approximated by a further-neighbor model on the corresponding line-graph lattice that is non-bipartite, thus broadening the space of candidate materials that may support the spiral spin liquid phases. As illustrations, we examine neutron scattering experiments performed on two spinel compounds, ZnCr$_2$Se$_4$ and CuInCr$_4$Se$_8$, to demonstrate the feasibility of this new approach and expose its possible limitations in experimental realizations., Comment: 20 pages, 18 figures

Geometrically frustrated systems play an important role in studying new physical phenomena and unconventional thermodynamics. Charge ordered defect pyrochlores AM2+M3+F6 offer a convenient platform for probing the interplay between electron distribution over M2+ and M3+ sites and structural distortions; however, they are limited to compounds with M2+/3+ = V, Fe, Ni, and Cu due to difficulties in the simultaneous stabilization of other 3d elements in the +2 and +3 oxidation states. Herein, we employ Cl- anions under hydrothermal conditions for the mild reduction of Mn2O3 in concentrated HF to obtain the CsMn2+Mn3+F6 composition as a phase pure sample and study its properties. The magnetism of CsMn2F6 was characterized by measuring the magnetic susceptibility and isothermal magnetization data, and a magnetic transition to a canted antiferromagnet state was found at 24.1 K. We determined the magnetic structure of CsMn2F6 using powder neutron diffraction, which revealed successive long-range ordering of the Mn2+ and Mn3+ sites that is accompanied by a second transition. The role and strength of magnetic exchange interactions were characterized using DFT calculations.

We present a study on the nuclear and magnetic structures of two iron-based garnets with magnetic cations isolated on tetrahedral sites. Ca\(_2\)YZr\(_2\)Fe\(_3\)O\(_{12}\) and Ca\(_2\)LaZr\(_2\)Fe\(_3\)O\(_{12}\) offer an interesting comparison for examining the effect of increasing cation size within the diamagnetic backbone of the garnet crystal structure, and how such changes affect the magnetic order. Despite both systems exhibiting well-pronounced magnetic transitions at low temperatures, we also find evidence for diffuse magnetic scattering due to a competition between the nearest-neighbor, next nearest-neighbor, and so on, within the tetrahedral sites. This competition results in a complex noncollinear magnetic structure on the tetrahedral sublattice creating a mixture of ferro- and antiferromagnetic interactions above the long-range ordering temperature near 20 K and suggests that the cubic site of the garnet plays a significant role in mediating the superexchange interactions between tetrahedral cations.

The VERsatile DIffractometer will set a new standard for a world-class magnetic diffractometer with versatility for both powder and single crystal samples and capability for wide-angle polarization analysis. The instrument will utilize a large single-frame bandwidth and will offer high-resolution at low momentum transfers and excellent signal-to-noise ratio. A horizontal elliptical mirror concept with interchangeable guide pieces will provide high flexibility in beam divergence to allow for a high-resolution powder mode, a high-intensity single crystal mode, and a polarized beam option. A major science focus will be quantum materials that exhibit emergent properties arising from collective effects in condensed matter. The unique use of polarized neutrons to isolate the magnetic signature will provide optimal experimental input to state-of-the-art modeling approaches to access detailed insight into local magnetic ordering.

Hexagonal iron sulfide exhibits a fascinating coexistence of metal–insulator, structural and magnetic transitions, reflecting an intimate interplay of its spin, phonon and charge degrees of freedom. Here, we show how a subtle competition of energetic and entropic free-energy components governs its thermodynamics and the sequence of phase transitions it undergoes upon cooling. By means of comprehensive neutron and X-ray scattering measurements, and supported by first-principles electronic structure simulations, we identify the critical role of the coupling between antiferromagnetic ordering and instabilities of anharmonic phonons in the metallic phase in driving the metal–insulator transition. The antiferromagnetic ordering enables the emergence of two zone-boundary soft phonons, whose coupling to a zone-centre mode drives the lattice distortion opening the electronic bandgap. Simultaneously, spin–lattice coupling opens a gap in the magnon spectrum that controls the entropy component of the metal–insulator transition free energy. These results reveal the importance of spin–phonon coupling to tune anharmonic effects, thus opening new avenues to design novel technologically important materials harbouring the metal–insulator transition and magnetoelectric behaviours. A detailed and systematic X-ray and neutron scattering study of hexagonal iron sulfide uncovers the critical role of spin–phonon coupling in promoting the metal–insulator transition in this system.

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo2/3RE1/3)(2)AlC with RE = Dy and Tb. Temperature and field-dependent magnetization as well as heat capacity were measured on a powder sample and on a single crystal allowing the construction of the magnetic field-temperature phase diagram. To study the magnetic structure of each magnetic phase, we applied neutron diffraction in a magnetic field up to 6 T. For (Mo2/3Dy1/3)(2)AlC in zero field, a spin density wave is stabilized at 16 K, with antiferromagnetic ordering at 13 K. Furthermore, we identify the coexistence of ferromagnetic and antiferromagnetic phases induced by magnetic fields for both RE = Tb and Dy. The origin of the field induced phases is resulting from the competing ferromagnetic and antiferromagnetic interactions. Funding Agencies|Knut and AliceWallenberg (KAW) FoundationKnut & Alice Wallenberg Foundation [KAW 2020.0033]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [CRC/TRR 270, 405553726]; ANR projectFrench National Research Agency (ANR) [ANR-18-CE09-0041]; government of the Russian Federation [075-15-2019-1886]; Flag-ERA JTC 2017

Geometrically frustrated systems play an important role in studying new physical phenomena and unconventional thermodynamics. Charge ordered defect pyrochlores

We report a comprehensive investigation of $L{n}_{2}{\mathrm{NiIrO}}_{6}$ ($Ln=\text{La}$, Pr, Nd) using thermodynamic and transport properties, neutron powder diffraction, resonant inelastic x-ray scattering, and density-functional theory (DFT) calculations to investigate the role of A-site cations on the magnetic interactions in this family of hybrid $3d\text{\ensuremath{-}}5d\text{\ensuremath{-}}4f$ compositions. Magnetic structure determination using neutron diffraction reveals antiferromagnetism for ${\mathrm{La}}_{2}{\mathrm{NiIrO}}_{6}$, a collinear ferrimagnetic Ni and Ir state that is driven to long-range antiferromagnetism upon the onset of Nd ordering in ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$, and a noncollinear ferrimagnetic Ni and Ir sublattice interpenetrated by a ferromagnetic Pr lattice for ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$. For ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$, heat-capacity results reveal the presence of two independent magnetic sublattices, and transport resistivity indicates insulating behavior and a conduction pathway that is thermally mediated. A first principles DFT calculation elucidates the existence of the two independent magnetic sublattices within ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and offers insight into the behavior in ${\mathrm{La}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$. Resonant inelastic x-ray scattering is consistent with spin-orbit coupling splitting the ${t}_{2g}$ manifold of octahedral ${\mathrm{Ir}}^{4+}$ into a ${J}_{\mathrm{eff}}=\frac{1}{2}$ and ${J}_{\mathrm{eff}}=\frac{3}{2}$ state for all members of the series considered.

Nd-based pyrochlore oxides have garnered significant interest owing to the moment-fragmentation physics observed in Nd${}_{2}$Zr${}_{2}$O${}_{7}$ and speculated in Nd${}_{2}$Hf${}_{2}$O${}_{7}$. Notably, this phenomenon is absent in Nd${}_{2}$Sn${}_{2}$O${}_{7}$, which features a smaller $B$-site ionic radius. Here, bulk characterization and neutron scattering measurements reveal a similar absence of moment fragmentation in Nd${}_{2}$GaSbO${}_{7}$, which is characterized by significant $B$-site disorder and an extremely small average ionic radius on the $B$ site. These results may indicate that chemical pressure (and not necessarily the $B$-site disorder) plays a key role in the presence or absence of this exotic phenomenon.

We report for the first time the magnetic structure of the high entropy oxide $(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})O$ using neutron powder diffraction. This material exhibits a sluggish magnetic transition but possesses a long-range ordered antiferromagnetic ground state, as revealed by DC and AC magnetic susceptibility, elastic and inelastic neutron scattering measurements. The magnetic propagation wavevector is k=(1/2, 1/2, 1/2) based on the cubic structure Fm-3m, and the magnetic structure consists of ferromagnetic sheets in the (111) planes with spins antiparallel between two neighboring planes. Inelastic neutron scattering reveals strong magnetic excitations at 100 K that survive up to room temperature. This work demonstrates that entropy-stabilized oxides represent a unique platform to study long range magnetic order with extreme chemical disorder., Comment: 13 pages, 4 figures, supplemental material is upon request

Two-dimensional materials with intrinsic functionality are becoming increasingly important in exploring fundamental condensed matter science and for developing advanced technologies. Bulk crystals that can be exfoliated are particularly relevant to these pursuits as they provide the opportunity to study the role of physical dimensionality and explore device physics in highly crystalline samples and designer heterostructures in a routine manner. Magnetism is a key element in these endeavors; however, relatively few cleavable materials are magnetic and none possess magnetic order at ambient conditions. Here, we introduce Fe5- xGeTe2 as a cleavable material with ferromagnetic behavior at room temperature. We established intrinsic magnetic order at room temperature in bulk crystals ([Formula: see text] = 310 K) through magnetization measurements and in exfoliated, thin flakes ([Formula: see text] ≈ 280 K) using the anomalous Hall effect. Our work reveals Fe5GeTe2 as a prime candidate for incorporating intrinsic magnetism into functional van der Waals heterostructures and devices near room temperature.

We present the results of a crystallographic analysis, magnetic characterization including neutron powder diffraction, and theoretical assessment of K2ReI6 prepared using solvent reactions. K2ReI6 crystallizes in the space group P21/n with an inversion center. Magnetic measurements of K2ReI6 sample indicate dominant antiferromagnetic coupling with a Curie–Weiss temperature of θW = −63.3(1) K, effective magnetic moment ∼2.64 μB/Re but show a weak ferromagnetism ordered at ∼24 K. Neutron powder diffraction indicates long-range order of the Re spins below 24 K, with an ordered magnetic moment of 2.2(1) μB/Re at 1.5 K. Therefore, a canted antiferromagnetic structure is concluded. The electronic structures using first-principles calculations suggest that the antiferromagnetic model of K2ReI6 yields the lowest total energy and opens a band gap with ∼1.0 eV width, which is consistent with the UV–vis–NIR optical measurements. After including the spin–orbit coupling (SOC) into the calculation, the band degeneracie...

The magnetic ground state of the pyrochlore Yb2GaSbO7 has not been established. The persistent spin fluctuations observed by muon spin-relaxation measurements at low temperatures have not been adequately explained for this material using existing theories for quantum magnetism. Here we report on the synthesis and characterisation of Yb2GaSbO7 to revisit the nature of the magnetic ground state. Through DC and AC magnetic susceptibility, heat capacity, and neutron scattering experiments, we observe evidence for a dynamical ground state that makes Yb2GaSbO7 a promising candidate for disorder-induced spin-liquid or spin-singlet behaviour. This state is quite fragile, being tuned to a splayed ferromagnet in a modest magnetic field μ0Hc ~ 1.5 T.

Using neutron powder diffraction and magnetic susceptibility measurements, we report on the preparation and characterization of the temperature- and field-dependent properties of CaY2ZrFe4O12, a co...

Thermomagnetic and inelastic neutron-scattering measurements on ${\mathrm{Na}}_{2}\mathrm{Pr}{\mathrm{O}}_{3}$ are reported. This material is an antiferromagnetic honeycomb magnet based on the tetravalent lanthanide ${\mathrm{Pr}}^{4+}$ and has been proposed to host dominant antiferromagnetic Kitaev interactions. These measurements reveal magnetic fluctuations in ${\mathrm{Na}}_{2}\mathrm{Pr}{\mathrm{O}}_{3}$ below an energy of 2 meV as well as crystal-field excitations around 230 meV. The latter energy is comparable to the scale of the spin-orbit interaction and explains both the very small effective moment of around $1.0\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per ${\mathrm{Pr}}^{4+}$ and the difficulty to uncover any static magnetic scattering below the ordering transition at ${T}_{\mathrm{N}}=$ 4.6 K. By comparing the low-energy magnetic excitations in ${\mathrm{Na}}_{2}\mathrm{Pr}{\mathrm{O}}_{3}$ to those of the isostructural spin-only compound, ${\mathrm{Na}}_{2}\mathrm{Tb}{\mathrm{O}}_{3}$, a microscopic model of exchange interactions is developed that implicates dominant and surprisingly large Heisenberg exchange interactions $J\ensuremath{\approx}1.1(1)$ meV. Although antiferromagnetic Kitaev interactions with $\mathit{\text{K}}\ensuremath{\le}0.2J$ cannot be excluded, the inelastic neutron-scattering data of ${\mathrm{Na}}_{2}\mathrm{Pr}{\mathrm{O}}_{3}$ is best explained with a $\mathrm{\ensuremath{\Delta}}=1.22$ easy-axis XXZ exchange anisotropy.

PbMO3 (M = 3d transition metals) family shows systematic variations in charge distribution and intriguing physical properties due to its delicate energy balance between Pb 6s and transition metal 3d orbitals. However, the detailed structure and physical properties of PbFeO3 remain unclear. Herein, we reveal that PbFeO3 crystallizes into an unusual 2ap × 6ap × 2ap orthorhombic perovskite super unit cell with space group Cmcm. The distinctive crystal construction and valence distribution of Pb2+0.5Pb4+0.5FeO3 lead to a long range charge ordering of the -A-B-B- type of the layers with two different oxidation states of Pb (Pb2+ and Pb4+) in them. A weak ferromagnetic transition with canted antiferromagnetic spins along the a-axis is found to occur at 600 K. In addition, decreasing the temperature causes a spin reorientation transition towards a collinear antiferromagnetic structure with spin moments along the b-axis near 418 K. Our theoretical investigations reveal that the peculiar charge ordering of Pb generates two Fe3+ magnetic sublattices with competing anisotropic energies, giving rise to the spin reorientation at such a high critical temperature., PbFeO3 is part of a family of lead based perovskites with many intriguing properties; however, difficulties in synthesis have hampered investigation. Here, the authors present a detailed study of the structure of PbFeO3 observing unique charge ordering and spin orientation among the constituent ions.

Two-dimensional van der Waals compounds with magnetic ions on a honeycomb lattice are hosts to a variety of exotic behavior. The magnetic interactions in one such compound, $\mathrm{Mn}\mathrm{P}{\mathrm{Se}}_{3}$, are investigated with elastic and inelastic neutron scattering. Magnetic excitations are observed in the magnetically ordered regime and persist to temperatures well above the ordering temperature, ${T}_{\text{N}}=74\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, consistent with low dimensional magnetic interactions. The inelastic neutron scattering results allow a model spin Hamiltonian to be presented that includes dominant intralayer interactions of ${J}_{1ab}=0.45$ meV, ${J}_{2ab}=0.03$ meV, ${J}_{3ab}=0.19$ meV, consistent with theoretical predictions. Despite the quasi-2D behavior, appreciable interlayer interactions of ${J}_{c}=0.031(5)$ meV are required to model the data. No evidence for anisotropy in the form of a spin gap is observed in the data collected. The measurements on $\mathrm{Mn}\mathrm{P}{\mathrm{Se}}_{3}$ are contrasted with those on $\mathrm{Mn}\mathrm{P}{\mathrm{S}}_{3}$ and reveal a large increase in the interlayer exchange interaction in $\mathrm{Mn}\mathrm{P}{\mathrm{Se}}_{3}$ that may stabilize the similar ordering temperatures in the bulk compounds.

We investigate the physical properties of the Shastry-Sutherland lattice material BaNd$_2$ZnO$_5$. Neutron diffraction, magnetic susceptibility, and specific heat measurements reveal antiferromagnetic order below 1.65 K. The magnetic order is found to be a 2-$\boldsymbol{Q}$ magnetic structure with the magnetic moments lying in the Shastry-Sutherland lattice planes comprising the tetragonal crystal structure of BaNd$_2$ZnO$_5$. The ordered moment for this structure is 1.9(1) $\mu_B$ per Nd ion. Inelastic neutron scattering measurements reveal that the crystal field ground state doublet is well separated from the first excited state at 8 meV. The crystal field Hamiltonian is determined through simultaneous refinement of models with both the LS coupling and intermediate coupling approximations to the inelastic neutron scattering and magnetic susceptibility data. The ground state doublet indicates that the magnetic moments lie primarily in the basal plane with magnitude consistent with the size of the determined ordered moment., Comment: 13 pages, 8 figures

Heavy transition metal magnets with ${J}_{eff}=\frac{1}{2}$ electronic ground states have attracted recent interest due to their penchant for hosting new classes of quantum spin liquids and superconductors. Unfortunately, model systems with ideal ${J}_{eff}=\frac{1}{2}$ states are scarce due to the importance of noncubic local distortions in most candidate materials. In this work, we identify a family of iridium halide systems [i.e., ${\mathrm{K}}_{2}\mathrm{Ir}{\mathrm{Cl}}_{6}$, ${\mathrm{K}}_{2}\mathrm{Ir}{\mathrm{Br}}_{6}$, ${({\mathrm{NH}}_{4})}_{2}\mathrm{Ir}{\mathrm{Cl}}_{6}$, and ${\mathrm{Na}}_{2}\mathrm{Ir}{\mathrm{Cl}}_{6}\ifmmode\cdot\else\textperiodcentered\fi{}6({\mathrm{H}}_{2}\mathrm{O})]$ with ${\mathrm{Ir}}^{4+}$ electronic ground states exhibiting extremely small deviations from the ideal ${J}_{eff}=\frac{1}{2}$ limit. We also find ordered magnetic ground states for the three anhydrous systems, with single-crystal neutron diffraction on ${\mathrm{K}}_{2}\mathrm{Ir}{\mathrm{Br}}_{6}$ revealing type-I antiferromagnetism. This spin configuration is consistent with expectations for significant Kitaev exchange in a face-centered-cubic magnet. This work establishes that incorporating isolated $\mathrm{Ir}{X}_{6}$ octahedra in materials, where $X$ is a halogen ion with a low electronegativity, is an effective design principle for realizing unprecedented proximity to the pure ${J}_{eff}=\frac{1}{2}$ state. At the same time, we highlight undeniable deviations from this ideal state, even in clean materials with ideal $\mathrm{Ir}{X}_{6}$ octahedra as inferred from the global cubic crystal structures.

We present a comprehensive neutron scattering study of the breathing pyrochlore magnet LiGaCr_{4}S_{8}. We observe an unconventional magnetic excitation spectrum with a separation of high- and low-energy spin dynamics in the correlated paramagnetic regime above a spin-freezing transition at 12(2) K. By fitting to magnetic diffuse-scattering data, we parametrize the spin Hamiltonian. We find that interactions are ferromagnetic within the large and small tetrahedra of the breathing pyrochlore lattice, but antiferromagnetic further-neighbor interactions are also essential to explain our data, in qualitative agreement with density-functional-theory predictions [Ghosh et al., npj Quantum Mater. 4, 63 (2019)2397-464810.1038/s41535-019-0202-z]. We explain the origin of geometrical frustration in LiGaCr_{4}S_{8} in terms of net antiferromagnetic coupling between emergent tetrahedral spin clusters that occupy a face-centered-cubic lattice. Our results provide insight into the emergence of frustration in the presence of strong further-neighbor couplings, and a blueprint for the determination of magnetic interactions in classical spin liquids.

Spin-$1/2$ antiferromagnetic triangular lattice models are paradigms of geometrical frustration, revealing very different ground states and quantum effects depending on the nature of anisotropies in the model. Due to strong spin orbit coupling and crystal field effects, rare-earth ions can form pseudospin-$1/2$ magnetic moments with anisotropic single-ion and exchange properties. Thus, rare-earth-based triangular lattices enable the exploration of this interplay between frustration and anisotropy. Here we study one such case, the rare-earth double vanadate glaserite material ${\mathrm{K}}_{3}\mathrm{Er}{({\mathrm{VO}}_{4})}_{2}$, which is a quasi-two-dimensional (2D) isosceles triangular antiferromagnet. Our specific heat and neutron powder diffraction data from ${\mathrm{K}}_{3}{\mathrm{Er}(\mathrm{VO}}_{4}{)}_{2}$ reveal a transition to long range magnetic order at ${T}_{N}=155\ifmmode\pm\else\textpm\fi{}5$ mK which accounts for all $Rln2$ entropy. We observe what appears to be a coexistence of three-dimensional (3D) and quasi-2D order below ${T}_{N}$. The quasi-2D order leads to an anisotropic Warren-like peak profile for $(hk0)$ reflections, while the 3D order is best-described by layers of antiferromagnetic $b$-aligned moments alternating with layers of zero moment. Our magnetic susceptibility data reveal that ${\mathrm{Er}}^{3+}$ takes on a strong $XY$ single-ion anisotropy in ${\mathrm{K}}_{3}\mathrm{Er}{({\mathrm{VO}}_{4})}_{2}$, leading to vanishing moments when pseudospins are oriented along $c$. Thus, the magnetic structure, when considered from the pseudospin point of view could comprise of alternating layers of $b$-axis and $c$-axis aligned antiferromagnetism.

Molecular magnets based on heavy transition metals have recently attracted significant interest in the quest for novel magnetic properties. For systems with an odd number of valence electrons per molecule, high or low molecular spin states are typically expected in the double exchange or quasimolecular orbital limits, respectively. In this work, we use bulk characterization, muon spin relaxation, neutron diffraction, and inelastic neutron scattering to identify a rare intermediate spin-3/2 per dimer state in the 6H-perovskite ${\mathrm{Ba}}_{3}{\mathrm{LaRu}}_{2}{\mathrm{O}}_{9}$ that cannot be understood in a double exchange or quasimolecular orbital picture and instead arises from orbital-selective Mott insulating behavior at the molecular level. Our measurements are also indicative of collinear stripe magnetic order below ${T}_{N}=26(1)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ for these molecular spin-3/2 degrees-of-freedom, which is consistent with expectations for an ideal triangular lattice with significant in-plane next nearest-neighbor exchange. Finally, we present neutron diffraction and Raman scattering data under applied pressure that reveal low-lying structural and spin state transitions at modest pressures $P\phantom{\rule{4pt}{0ex}}\ensuremath{\le}$ 1 GPa, which highlights the delicate balance between competing energy scales in this system.

We present a comprehensive neutron scattering study of the breathing pyrochlore magnet LiGaCr_{4}S_{8}. We observe an unconventional magnetic excitation spectrum with a separation of high- and low-energy spin dynamics in the correlated paramagnetic regime above a spin-freezing transition at 12(2) K. By fitting to magnetic diffuse-scattering data, we parametrize the spin Hamiltonian. We find that interactions are ferromagnetic within the large and small tetrahedra of the breathing pyrochlore lattice, but antiferromagnetic further-neighbor interactions are also essential to explain our data, in qualitative agreement with density-functional-theory predictions [Ghosh et al., npj Quantum Mater. 4, 63 (2019)2397-464810.1038/s41535-019-0202-z]. We explain the origin of geometrical frustration in LiGaCr_{4}S_{8} in terms of net antiferromagnetic coupling between emergent tetrahedral spin clusters that occupy a face-centered-cubic lattice. Our results provide insight into the emergence of frustration in the presence of strong further-neighbor couplings, and a blueprint for the determination of magnetic interactions in classical spin liquids.

High-resolution resonant inelastic x-ray scattering measurements ($\mathrm{\ensuremath{\Delta}}E=46\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$) have been performed on ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$ through the metal-to-insulator transition (MIT). A magnetic excitation at 125 meV evolves continuously through the MIT, in agreement with recent Raman-scattering results, and provides further confirmation for an all-in all-out magnetic ground state. Asymmetry of this feature is likely a result of coupling between the electronic and the magnetic degrees of freedom. We also observe a broad continuum of interband excitations centered at 0.3 eV energy loss. This is indicative of significant hybridization between Os $5d$ and O $2p$ states and the concurrent itinerant nature of the system. In turn, this suggests a possible breakdown of the free-ion model for ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$.

${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ is a layered van der Waals magnetic material with a relatively high ordering temperature and large anisotropy. While most studies have concluded the interlayer ordering to be ferromagnetic, there have also been reports of interlayer antiferromagnetism in ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$. Here, we investigate the interlayer magnetic ordering by neutron diffraction experiments, scanning tunneling microscopy (STM) and spin-polarized STM measurements, density functional theory plus U calculations, and STM simulations. We conclude that the layers of ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ are coupled ferromagnetically and that in order to capture the magnetic and electronic properties of ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ within density functional theory, Hubbard U corrections need to be taken into account.

Ising-like spin-1/2 magnetic materials are of interest for their ready connection to theory, particularly in the context of quantum critical behavior. In this work we report detailed studies of the magnetic properties of a member of the rare earth pyrosilicate family, D-Er$_{2}$Si$_{2}$O$_{7}$, which is known to display a highly anisotropic Ising-like g-tensor and effective spin-1/2 magnetic moments. We used powder neutron diffraction, powder inelastic neutron spectroscopy (INS), and single crystal AC susceptibility to characterize its magnetic properties. Neutron diffraction enabled us to determine the magnetic structure below the known transition temperature ($T_{N}$ = 1.9 K) in zero field, confirming that the magnetic state is a four-sublattice antiferromagnetic structure with two non-collinear Ising axes, as was previously hypothesized. Our powder INS data revealed a gapped excitation at zero field, consistent with anisotropic (possibly Ising) exchange. An applied field of 1 T produces a mode softening, which is consistent with a field-induced second order phase transition. To assess the relevance of D-Er$_{2}$Si$_{2}$O$_{7}$ to the transverse field Ising model, we performed AC susceptibility measurements on a single crystal with the magnetic field oriented in the direction transverse to the Ising axes. This revealed a transition at 2.65 T at 0.1 K, a field significantly higher than the mode-softening field observed by powder INS, showing that the field-induced phase transitions are highly field-direction dependent as expected. These measurements suggest that D-Er$_{2}$Si$_{2}$O$_{7}$ may be a candidate for further exploration related to the transverse field Ising model., Comment: AC suscep. data presented in the last version was incorrect. Revised with new data and conclusions

Y2CoRuO6 was synthesized as a B-site ordered double perovskite with distorted monoclinic P21/n symmetry and an average tilting of the CoO6 and RuO6 octahedra of ψ = 19.7°. DC magnetization measure...

A new uranium fluoride phosphate, UFPO4, was synthesized via a mild hydrothermal route and characterized optically, thermally, and magnetically. Two thermal transformation products, U2O(PO4)2 and U...

Li3((LiCr)(Te/Sb))O6 compounds where Cr atoms along with Li and Te or Sb are part of a honeycomb and are studied using magnetic susceptibility, specific heat, x-ray photoelectron spectroscopy and neutron diffraction. The oxides stoichiometries as determined from the neutron diffraction studies are Li4.47Cr0.53TeO6 and Li3.88Cr1.12SbO6 with a stable oxidation state of +3 for Cr. Both the compounds crystallize in space group C2/m with intermixing of cations at the 4g sites leaving the 2a sites preferentially for Te or Sb. Again, the Li+ ions alone predominantly occur in the interlayer sites. Both the compounds show a broad anomaly in specific heat at 8 K, which is robust against 8 T. A corresponding anomaly is absent in the magnetic susceptibility but recovers from its derivative, dχ(T)/dT. We ascertain the magnetic anomaly temperatures (T a ) of Li4.47Cr0.53TeO6 and Li3.88Cr1.12SbO6 as 5.9 K and 6.7 K respectively from specific heat. Although the physical properties indicated a low temperature anomaly, neutron diffraction data did not reveal a magnetic signal or a structural anomaly down to 1.5 K. This rules out a conventional long-range ordered magnetic ground state in either compounds. Combining the results from specific heat, neutron diffraction and electron paramagnetic resonance, we put forth a scenario of depleted honeycomb lattice of Cr3+ with predominant short-range magnetic correlations as the magnetic ground states of the title compounds.

Research on low-dimensional materials has increased drastically in the last decade, with the discovery of two-dimensional transition metal carbides and nitrides (MXenes) produced by atom-selective chemical etching of laminated parent ${M}_{n+1}A{X}_{n}$ (MAX) phases. Here, we apply density functional theory and subsequent materials synthesis and analysis to explore the phase stability and Mo/Sc intermixing on the M site in the chemically ordered quaternary $i\ensuremath{-}\mathrm{MAX}$ phase (${\mathrm{Mo}}_{x}{\mathrm{Sc}}_{1\ensuremath{-}x}{)}_{2}\mathrm{AlC}$. Transmission electron microscopy confirms the theoretical predictions of preferential in-plane ordering of Mo and Sc, with the highest crystal quality obtained for the ideal Mo:Sc ratio of 2:1 (predicted as the most stable), as well as a retained $i\ensuremath{-}\mathrm{MAX}$ structure even for an increased relative Sc content, with Sc partially occupying Mo sites. The results are supported by refined neutron diffraction data, which show space group $C2/c$ (no. 15), and a C occupancy of 1. Subsequent chemical etching produces MXene for $x=0.66$, while for $x=0.33$ and 0.5 no MXene is observed. These results demonstrate that a precise control of the $i\ensuremath{-}\mathrm{MAX}$ composition is crucial for derivation of MXene, with a MXene quality optimized for a Mo:Sc ratio of 2:1 with minimal intermixing between Mo and Sc.

We have synthesized the high-pressure form of $\mathrm{CrS}{\mathrm{b}}_{2}$ with $\mathrm{CuA}{\mathrm{l}}_{2}$-type structure under 7 GPa and 700 \ifmmode^\circ\else\textdegree\fi{}C, and characterized its structural, transport, and magnetic properties by a suite of measurement techniques over a broad range of temperature, magnetic field, and pressure. In addition to previously reported ferromagnetic (FM) transition at ${T}_{\mathrm{C}}\ensuremath{\approx}160$ K, we discover another antiferromagnetic spin-density-wave (SDW) transition at ${T}_{\mathrm{s}}\ensuremath{\approx}90$ K, which is characterized by FM sheets of spins in the $ab$ plane that vary along the $c$ axis as determined by neutron powered diffraction. Pronounced anomalies around these two magnetic transitions are visible only in the lattice parameter $c$, signaling a strong spin-lattice coupling along the -Cr-Cr-Cr- infinite linear chain. We find that the application of magnetic field can suppress the SDW phase and stabilize the FM state down to the lowest temperature above ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}}\ensuremath{\approx}3$ T, around which a peculiar non-Fermi-liquid behavior with reduced effective mass emerges. On the other hand, the application of high pressure induces complex evolution of the magnetic states, i.e., the FM order is lowered while the SDW order is enhanced quickly until they merge together into a single antiferromagnetic transition, which is suppressed completely at ${P}_{\mathrm{c}}\ensuremath{\approx}9$ GPa. We observe near ${P}_{\mathrm{c}}$ non-Fermi-liquid behavior and enhancement of effective mass, which indicates the possible occurrence of magnetic quantum critical point. No superconductivity was observed down to 2 K around ${P}_{\mathrm{c}}$.

Kitaev materials, based on bond-directional Ising interactions, offer an intriguing platform for hosting exotic magnetic ground states and excitations. Significant Kitaev interactions are most commonly realized in heavy transition metal magnets with so-called ${J}_{\mathrm{eff}}$ = \textonehalf{} electronic ground states for the transition metal and local geometries consisting of metal-ligand edge-sharing octahedra. Here, the authors show that Kitaev materials can also be realized in ${J}_{\mathrm{eff}}$ = \textonehalf{} magnets via extended superexchange pathways mediated by more than one anion.

The negative thermal expansion (NTE) in CuO is explained via electron-transfer-driven superexchange interaction. The elusive connection between the spin-lattice coupling and NTE of CuO is investigated by neutron scattering and principal strain axes analysis. The density functional theory calculations show as the temperature decreases, the continuously increasing electron transfer accounts for enhancing the superexchange interaction along [101̅], the principal NTE direction. It is further rationalized that only when the interaction along [101̅] is preferably enhanced to a certain level compared to the other competing antiferromagnetic exchange pathways can the corresponding NTE occur. Outcomes from this work have implications for controlling the thermal expansion through superexchange interaction, via, for example, optical manipulation, electron or hole doping, etc.

${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ is an itinerant ferromagnet composed of two-dimensional layers weakly connected by van der Waals bonding that shows a variety of intriguing phenomena. Inelastic neutron scattering measurements on bulk single crystals of ${\mathrm{Fe}}_{2.75}{\mathrm{GeTe}}_{2}$ were performed to quantify the magnetic exchange interaction energies and anisotropy. The observed inelastic excitations, which extend to a maximum energy of $\ensuremath{\sim}75$ meV, are indicative of dominant in-plane correlations with negligible magnetic interactions between the layers. A spin gap of 3.7 meV is observed, allowing a measure of the magnetic anisotropy. The excitations are damped, reflective of both the magnetic site occupancy reduction of 25% on one Fe sublattice and the itinerant interactions. A minimal model is employed to describe the excitation spectra and extract magnetic exchange interaction values. The temperature evolution of the excitations are probed and correlations shown to persist above ${T}_{c}$, further supporting the low-dimensional nature of the magnetism.

Two-dimensional materials with intrinsic functionality are becoming increasingly important in exploring fundamental condensed matter science and for developing advanced technologies. Bulk crystals that can be exfoliated are particularly relevant to these pursuits as they provide the opportunity to study the role of physical dimensionality and explore device physics in highly crystalline samples and designer heterostructures in a routine manner. Magnetism is a key element in these endeavors; however, relatively few cleavable materials are magnetic and none possess magnetic order at ambient conditions. Here, we introduce Fe