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The desire to increase the energy density of stoichiometric layered LiTMO2 (TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true O-redox, as observed in Li-excess cathodes. Through a high-resolution O K-edge resonant inelastic X-ray spectroscopy (RIXS) study of the Mn-free Ni-rich layered oxide, LiNi0.98W0.02O2, we demonstrate that the same oxidized oxygen environment exists in both Li-excess and non-Li-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.

Resonant inelastic x-ray scattering (RIXS) using an incident energy tuned to the uranium N 4,5 absorption edges is reported from epitaxial films of α-U3O8 and UN. Theory shows that for U3O8 the multiplets associated with a 5f 1 configuration with a ground state of 2 F 5/2 and the excited state of 2 F 7/2 are observed. However, the strong transition predicted at a transfer energy of 1.67 eV is not observed. We assume this is a consequence of the intermediate state lifetime broadening due to interaction with continuum states when the transferred energy exceeds the onset of the continuum in the presence of the core hole. This hypothesis is supported by the results obtained for the 5f-itinerant system UN, where no sharp transitions have been observed, although the broad scattering response centered at ∼ 1 eV is considered a signature of a predominantly 5f 3 configuration in this band-like semi-metallic system. These experiments and theory add important information on these materials, both of which have been investigated since the 1960s, as well as whether RIXS at the uranium N edge can become a valuable tool for actinide research.

Single lanthanide atoms and molecules are promising candidates for atomic data storage and quantum logic due to the long lifetime of their magnetic quantum states. Accessing and controlling these states through electrical transport requires precise knowledge of their electronic configuration at the level of individual atomic orbitals, especially of the outer shells involved in transport. However, no experimental techniques have so far shown the required sensitivity to probe single atoms with orbital selectivity. Here we resolve the magnetism of individual orbitals in Gd and Ho single atoms on MgO/Ag(100) by combining X-ray magnetic circular dichroism with multiplet calculations and density functional theory. In contrast to the usual assumption of bulk-like occupation of the different electronic shells, we establish a charge transfer mechanism leading to an unconventional singly ionized configuration. Our work identifies the role of the valence electrons in determining the quantum level structure and spin-dependent transport properties of lanthanide-based nanomagnets.

B-site Os-doped quadruple perovskite oxides LaCu3Fe4-xOsxO12 (x = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCu3Fe4O12 experiences Cu-Fe intermetallic charge transfer that changes the Cu3+/Fe3+ charge combination to Cu2+/Fe3.75+ at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os6+ and mixed Os4.5+ valence states are determined by X-ray absorption spectroscopy for x = 1 and x = 2 compositions, respectively. The x = 1 sample crystallizes in an Fe/Os disordered structure with the Im3 space group. It experiences a spin-glass transition around 480 K. With further Os substitution up to x = 2, the crystal symmetry changes to Pn3, where Fe and Os are orderly distributed in a rocksalt-type fashion at the B site. Moreover, this composition shows a long-range Cu2+(↑)Fe3+(↑)Os4.5+(↓) ferrimagnetic ordering near 520 K. This work provides a rare example for 5d substitution-suppressed intermetallic charge transfer as well as induced structural and magnetic phase transitions with high spin ordering temperature.

Complex oxides show extreme sensitivity to structural distortions and defects, and the intricate balance of competing interactions which emerge at atomically defined interfaces may give rise to unexpected physics. In the interfaces of non-magnetic complex oxides, one of the most intriguing properties is the emergence of magnetism which is sensitive to chemical defects. Particularly, it is unclear which defects are responsible for the emergent magnetic interfaces. Here, we show direct and clear experimental evidence, supported by theoretical explanation, that the B-site cation stoichiometry is crucial for the creation and control of magnetism at the interface between non-magnetic ABO3-perovskite oxides, LaAlO3 and SrTiO3. We find that consecutive defect formation, driven by atomic charge compensation, establishes the formation of robust perpendicular magnetic moments at the interface. Our observations propose a route to tune these emerging magnetoelectric structures, which are strongly coupled at the polar-nonpolar complex oxide interfaces., In the interfaces of non-magnetic complex oxides, it is unclear which defects are responsible for the magnetic interfaces. Here, the authors find the B-site cation stoichiometry is crucial for the creation and control of magnetism at the interface between non-magnetic ABO3-perovskite oxides.

The report on the superconductivity of the two-legged spin ladders BaFe2S3 and BaFe2Se3 has established 123-type iron chalcogenides as a novel subgroup in the iron-based superconductor family and has stimulated the continuous exploration of other iron-based materials with new structures and potentially novel properties. In this paper, we report the systematic study of a new quasi-one-dimensional (1D) iron-based compound, Ba9Fe3Te15, including its synthesis and magnetic properties. The high-pressure synthesized Ba9Fe3Te15 crystallized in a hexagonal structure that mainly consisted of face-sharing FeTe6 octahedral chains running along the c axis, with a lattice constant of a = 10.23668 A; this led to weak interchain coupling and an enhanced one-dimensionality. The systematic static and dynamic magnetic properties were comprehensively studied experimentally. The dc magnetic susceptibility showed typical 1D antiferromagnetic characteristics, with a Tmax at 190 K followed by a spin glass (SG) state with freezing at Tf ≈ 6.0 K, which were also unambiguously proved by ac susceptibility measurements. Additionally, X-ray magnetic circular dichroism (XMCD) experiments revealed an unexpected orbital moment for Fe2+, i.e., 0.84 μB per Fe in Ba9Fe3Te15. The transport property is electrically insulating, with a thermal activation gap of 0.32 eV. These features mark Ba9Fe3Te15 as an alternative type of iron-based compound, providing a diverse candidate for high-pressure studies in order to pursue some emerging physics.

In materials science, much effort has been devoted to the reproduction of superconductivity in chemical compositions, analogous to cuprate superconductors since their discovery over 30 years ago. This approach was recently successful in realising superconductivity in infinite-layer nickelates

International audience; Using a highly stoichiometric magnetite, the pressure-induced phase transitions of Fe3O4 have been revisited here by performing Fe K-edge X-ray absorption and magnetic circular dichroism measurements up to P = 65 GPa at room temperature and 71 GPa at 20 K. We have observed a structural transition at around 27 GPa from magnetite to a high-pressure phase h-Fe3O4 with the loss of the net ordered magnetic moments for both temperatures. The orthorhombic CaTi2O4-type (Bbmm) structure of the high-pressure phase h-Fe3O4 has been determined by combining experimental studies and theoretical simulations of the Fe K-edge X-ray absorption near-edge structure spectra. The long-time discussed pressure induced spin crossover, and inverse to normal spinel structure transitions in Fe3O4 can be deterministically excluded from the present study up to ∼65 GPa.

The discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a new material class that mirrors the cuprate superconductors. Here, we report on magnetic excitations in these nickelates, measured using resonant inelastic x-ray scattering (RIXS) at the Ni L3-edge, to shed light on the material complexity and microscopic physics. Undoped NdNiO2 possesses a branch of dispersive excitations with a bandwidth of approximately 200 meV, reminiscent of strongly-coupled, antiferromagnetically aligned spins on a square lattice, despite a lack of evidence for long range magnetic order. The significant damping of these modes indicates the importance of coupling to rare-earth itinerant electrons. Upon doping, the spectral weight and energy decrease slightly, while the modes become overdamped. Our results highlight the role of Mottness in infinite-layer nickelates., This is the initially submitted version before revising for reviewers' comments. The peer-reviewed version has been accepted at Science and will be published soon

Layered Li-rich transition metal oxides undergo O-redox, involving the oxidation of the O2− ions charge compensated by extraction of Li+ ions. Recent results have shown that for 3d transition metal oxides the oxidized O2− forms molecular O2 trapped in the bulk particles. Other forms of oxidised O2− such as O22− or (O–O)n− with long bonds have been proposed, based especially on work on 4 and 5d transition metal oxides, where TM–O bonding is more covalent. Here, we show, using high resolution RIXS that molecular O2 is formed in the bulk particles on O2‒ oxidation in the archetypal Li-rich ruthenates and iridate compounds, Li2RuO3, Li2Ru0.5Sn0.5O3 and Li2Ir0.5Sn0.5O3. The results indicate that O-redox occurs across 3, 4, and 5d transition metal oxides, forming O2, i.e. the greater covalency of the 4d and 5d compounds still favours O2. RIXS and XAS data for Li2IrO3 are consistent with a charge compensation mechanism associated primarily with Ir redox up to and beyond the 5+ oxidation state, with no evidence of O–O dimerization., In this work, authors show that O-redox in 4d and 5d transition metal oxides involves the formation of molecular oxygen trapped in the particles. These results are in accord with observations in 3d oxides and show that the greater covalency of the 4d and 5d oxides does not stabilise peroxo-like species.

We have investigated the multiferroicity and magnetoelectric (ME) coupling in HoFeWO6. With a noncentrosymmetric polar structure (space group Pna21) at room temperature, this compound shows an onset of electric polarization with an antiferromagnetic ordering at the Néel temperature (TN ) of 17.8 K. The magnetic properties of the polycrystalline samples were studied by DC and AC magnetization and heat capacity measurements. The metamagnetic behavior at low temperatures was found to be directly related to the dielectric properties of the compound. In particular, field-dependent measurements of capacitance show a magnetocapacitance (MC) effect with double-hysteresis loop behavior in direct correspondence with the magnetization. Our x-ray diffraction results show the Pna21 structure down to 8 K and suggest the absence of a structural phase transition across TN . Soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism (XMCD) measurements at the Fe L2,3 and Ho M4,5 edges revealed the oxidation state of Fe and Ho cations to be 3+. Fe L2,3 XMCD further shows that Fe3+ cations are antiferromagnetically ordered in a noncollinear fashion with spins arranged 90◦ with respect to each other. Our findings show that HoFeWO6 is a type-II multiferroic exhibiting a MC effect. The observed MC effect and the change in polarization by the magnetic field, as well as their direct correspondence with magnetization, further support the strong ME coupling in this compound., The work at University of Houston (UH) is supported by U. S. Air Force Office of Scientific Research Grants FA9550-15-1-0236 and FA9550-20-1-0068, the T. L. L. Temple Foundation, the John J. and Rebecca Moores Endowment, and the State of Texas through the Texas Center for Superconductivity at the University of Houston. The XRD patterns were collected at the National Synchrotron Radiation Research Center at Taiwan. The synchrotron XAS/XMCD experiments were performed at the BOREAS beamline of the ALBA Synchrotron Light Facility in collaboration with ALBA staff. Computational resources were provided by the Extreme Science and Engineering Discovery Environment (XSEDE) [55] supported by the National Science Foundation (ACI-1548562) and the National Energy Research Scientific Computing (NERSC) Center, a DOE Office of Science User Facility supported by the Office of Science, U. S. Department of Energy, under Contract No. DE-AC02-05CH11231. Additional support for this work was provided through resources of the uHPC cluster managed by UH and acquired through NSF Award 1531814. The authors acknowledge the use of the Maxwell/Opuntia/Sabine Cluster and the advanced support from the Research Computing Data Core at UH. The work at National Sun Yat-Sen University was partially supported by the Ministry of Science and Technology of Taiwan under Grant No. MOST 109-2112-M-110-019.

A quadruple perovskite oxide $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{2}{\mathrm{Re}}_{2}{\mathrm{O}}_{12}$ was synthesized by high-pressure annealing. This compound crystallizes in an $A$- and $B$-site ordered quadruple perovskite structure with space group $Pn\text{\ensuremath{-}}3$. The charge combination is determined to be $\mathrm{Ca}{{\mathrm{Cu}}^{2+}}_{3}{{\mathrm{Co}}^{2+}}_{2}{{\mathrm{Re}}^{6+}}_{2}{\mathrm{O}}_{12}$ by bond valence sum analysis and x-ray absorption spectroscopy. In contrast to other isostructural $A{\mathrm{Cu}}_{3}{B}_{2}{B}_{2}^{\ensuremath{'}}{O}_{12}$ compounds with a single magnetic transition, a long-range antiferromagnetic phase transition originating from the ${A}^{\ensuremath{'}}$-site ${\mathrm{Cu}}^{2+}$ sublattice is found to occur at ${T}_{N}\ensuremath{\approx}28\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Subsequently, the spin coupling between the $B$-site ${\mathrm{Co}}^{2+}$ and ${B}^{\ensuremath{'}}$-site ${\mathrm{Re}}^{6+}$ ions contributes to a ferrimagnetic transition around ${T}_{\mathrm{C}}\ensuremath{\approx}20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Strong electrical insulating behavior is identified by optical measurement with an energy gap of approximately 3.75 eV. The mechanisms of the spin interactions are discussed in detail.

In materials science, much effort has been devoted to reproduce superconductivity in chemical compositions analogous to cuprate superconductors since their discovery over thirty years ago. This approach was recently successful in realising superconductivity in infinite-layer nickelates. Although differing from cuprates in electronic and magnetic properties, strong Coulomb interactions suggest infinite-layer nickelates have a propensity to various symmetry-breaking orders that populate the cuprates. Here we report the observation of charge density waves (CDWs) in infinite-layer NdNiO$_2$ films using Ni-$L_3$ resonant x-ray scattering. Remarkably, CDWs form in Nd 5$d$ and Ni 3$d$ orbitals at the same commensurate wavevector $(0.333, 0)\;r.l.u.$, with non-negligible out-of-plane dependence, and an in-plane correlation length up to $\sim$ 60 Angstrom. Spectroscopic studies reveal a strong connection between CDWs and the Nd 5$d$ - Ni 3$d$ orbital hybridisation. Upon entering the superconducting state at 20\% Sr doping, the CDWs disappear. Our work demonstrates the existence of CDWs in infinite-layer nickelates with a multi-orbital character distinct from cuprates, which establishes their low-energy physics., Comment: 9 pages, 4 figures, and Supplementary Information

The double perovskite oxide ${\mathrm{Sr}}_{2}\mathrm{CrOs}{\mathrm{O}}_{6}$ with a $3{d}^{3}\text{\ensuremath{-}}5{d}^{3}$ configuration exhibits very high-${T}_{C}$ ferrimagnetism (\ensuremath{\sim}725 K) at the end point of half-metallicity. Many substitution studies have been conducted theoretically and experimentally over the last two decades to shed more light on the open issue of how the $3{d}^{3}\text{\ensuremath{-}}5{d}^{3}$ configuration generates the high-${T}_{C}$ ferrimagnetic state and to accelerate development toward applications. We have succeeded in synthesizing a solid solution of ${\mathrm{Sr}}_{2}{\mathrm{Cr}}_{1--x}{\mathrm{Ni}}_{x}\mathrm{Os}{\mathrm{O}}_{6}$ under high-pressure and high-temperature conditions. ${\mathrm{Sr}}_{2}{\mathrm{Cr}}_{0.5}{\mathrm{Ni}}_{0.5}\mathrm{Os}{\mathrm{O}}_{6}$ exhibits magnetization sixfold greater ($\ensuremath{\sim}1.2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$/formula unit at 5 K) than that of ${\mathrm{Sr}}_{2}\mathrm{CrOs}{\mathrm{O}}_{6}$. This enhancement is preserved even at room temperature. X-ray absorption spectroscopy revealed that the electronic configuration is ${\mathrm{Sr}}_{2}{({{\mathrm{Cr}}^{3+}}_{2/3}{{\mathrm{Cr}}^{6+}}_{1/3})}_{0.5}{{\mathrm{Ni}}^{2+}}_{0.5}{\mathrm{Os}}^{5+}{\mathrm{O}}_{6}$, indicating that the valence state of Os does not change from the host state $[{\mathrm{Os}}^{5+}(5{d}^{3})]$. Instead, nonmagnetic ${\mathrm{Cr}}^{6+}(3{d}^{0})$ is partly generated among coexisting ${\mathrm{Cr}}^{3+}(3{d}^{3})$. X-ray magnetic circular dichroism measurements showed that the Os ions are antiferromagnetically coupled to the Cr and ferromagnetically to the Ni. The replacement of antiferromagnetic Cr by ferromagnetic Ni explains the increase of the net magnetism in this ferrimagnetic system. We infer that the strong antiferromagnetic exchange interaction of the $3{d}^{3}\text{\ensuremath{-}}5{d}^{3}$ configuration associated with the ${\mathrm{Cr}}^{3+}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}{\mathrm{Os}}^{5+}$ bond still accounts for the robust high-${T}_{C}$ ferrimagnetism of the Ni-substituted series. We deduce from the experiments that the ferromagnetic exchange interaction of the $3{d}^{8}\text{\ensuremath{-}}5{d}^{3}$ configuration of the ${\mathrm{Ni}}^{2+}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}{\mathrm{Os}}^{5+}$ is stronger than that of the $3{d}^{8}\text{\ensuremath{-}}3{d}^{3}$ configuration of the ${\mathrm{Ni}}^{2+}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}{\mathrm{Cr}}^{3+}$, suggesting that the larger 5d orbital of the Os allows for a stronger virtual hopping from the Ni than the smaller $3d$ orbital of the Cr. The present results can help to further develop practical materials and to resolve open issues concerning the relative strengths of the various exchange interactions.

The crystal-field ground state wave function of CeCu$_2$Si$_2$ has been investigated with linear polarized $M$-edge x-ray absorption spectroscopy from 250mK to 250K, thus covering the superconducting ($T_{\text{c}}$=0.6K), the Kondo ($T_{\text{K}}$$\approx$20K) as well as the Curie-Weiss regime. The comparison with full-multiplet calculations shows that the temperature dependence of the experimental linear dichroism is well explained with a $\Gamma_7^{(1)}$ crystal-field ground-state and the thermal population of excited states at around 30meV. The crystal-field scheme does not change throughout the entire temperature range thus making the scenario of orbital switching unlikely. Spectroscopic evidence for the presence of the Ce 4$f^0$ configuration in the ground state is consistent with the possibility for a multi-orbital character of the ground state. We estimate from the Kondo temperature and crystal-field splitting energies that several percents of the higher lying $\Gamma_6$ state and $\Gamma_7^{(2)}$ crystal-field states are mixed into the primarily $\Gamma_7^{(1)}$ ground state. This estimate is also supported by re-normalized band-structure calculations that uses the experimentally determined crystal-field scheme., Comment: 8 pages, 5 figures

Polycrystalline samples of $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ were synthesized at ambient pressure (AP) and high pressure (HP) conditions, respectively. Both samples are electrically semiconducting. The AP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ crystallizes in the $6H$ perovskite structure with space group $P{6}_{3}/mmc$, consisting of face-sharing $\mathrm{O}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ dimer units and corner-sharing $\mathrm{Ni}{\mathrm{O}}_{6}$ octahedra. Magnetic measurements indicated that AP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ is antiferromagnetically ordered below 130 K. HP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ crystallizes in the $6H$ perovskite structure too, but the face-sharing octahedral sites appear to be occupied by both $\mathrm{N}{\mathrm{i}}^{2+}$ and $\mathrm{O}{\mathrm{s}}^{5+}$ ions, whereas the corner-sharing site is occupied exclusively by $\mathrm{O}{\mathrm{s}}^{5+}$. HP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ undergoes a high-temperature ($\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}400\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) weak ferromagnetic transition, which is much different from the antiferromagnetism of the AP phase. The long-range magnetic order of HP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ was confirmed by neutron powder diffraction. X-ray magnetic circular dichroism analysis supported ferromagnetic coupling between Os and Ni moments which leads to a spin arrangement, where the ferromagnetic moments mainly arise from $\mathrm{N}{\mathrm{i}}^{2+}$ ions.

Cubic perovskite $\mathrm{BaFe}{\mathrm{O}}_{3}$ single crystals with stoichiometric oxygen content were successfully grown by a two-step method. With decreasing temperature, the crystal experiences a spin-glassy transition at ${T}_{\mathrm{SG}}\ensuremath{\approx}181\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, followed by a long-range spiral antiferromagnetic ordering at ${T}_{N}\ensuremath{\approx}117\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and then a third spin transition at ${T}_{N}^{\ensuremath{'}}\ensuremath{\approx}97\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, revealing the subtle magnetic competition and interactions. As a result, a smaller magnetic field (\ensuremath{\sim}0.4 T) can induce a metamagnetic transition towards a ferromagnetic state with the saturated magnetic moment about $3.2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ at 2 K. The easy magnetization axis looks to vary from the direction perpendicular to [111] to the [100] axis. Semiconducting behavior with a small activation energy is observed above ${T}_{\mathrm{N}}$, whereas the spiral spin ordering changes the electrical transport to be likely half-metallic with considerable negative magnetoresistance effect.

Spin state transitions and intermetallic charge transfers can essentially change material structural and physical properties while excluding external chemical doping. However, these two effects have rarely been found to occur sequentially in a specific material. In this article, we show the realization of these two phenomena in a perovskite oxide PbCoO

The development of high‐density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat‐assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin‐film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m-3 is combined with a saturation magnetization of μ0>7sub>Ms = 0.52 T at 2 K (2.2 MJ m-3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare‐earth‐free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m-1 K-1, make Rh2CoSb a candidate for the development of heat‐assisted writing with a recording density in excess of 10 Tb in.-2.

Room-temperature ferrimagnetism was discovered for the anti-site-disordered perovskite $\mathrm{C}{\mathrm{a}}_{2}\mathrm{MnOs}{\mathrm{O}}_{6}$ with ${T}_{\mathrm{c}}=305\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. $\mathrm{C}{\mathrm{a}}_{2}\mathrm{MnOs}{\mathrm{O}}_{6}$ crystallizes into an orthorhombic structure with a space group of Pnma, in which Mn and Os share the oxygen-coordinated-octahedral site at an equal ratio without a noticeable ordered arrangement. The material is electrically semiconducting with variable-range-hopping behavior. X-ray absorption spectroscopy confirmed the trivalent state of the Mn and the pentavalent state of the Os. X-ray magnetic circular dichroism spectroscopy reveals that the Mn and Os magnetic moments are aligned antiferromagnetically, thereby classifying the material as a ferrimagnet which is in accordance with band structure calculations. It is intriguing that the magnetic signal of the Os is very weak, and that the observed total magnetic moment is primarily due to the Mn. The ${T}_{\mathrm{c}}=305\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is the second highest in the material category of so-called disordered ferromagnets such as $\mathrm{CaR}{\mathrm{u}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}{\mathrm{O}}_{3}$, $\mathrm{SrR}{\mathrm{u}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{r}}_{x}{\mathrm{O}}_{3}$, and $\mathrm{CaI}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}{\mathrm{O}}_{3}$, and hence, may support the development of spintronic oxides with relaxed requirements concerning the anti-site disorder of the magnetic ions.

Materials with room-temperature two-dimensional itinerant ferromagnetism enable ultracompact device density and quantum computing in next-generation nano-spintronics. Among numerous candidates, perovskite-based heterostructures have offered an excellent platform to manipulate spin-orbital-charge coupling, unveiling a series of emergent spin-dependent phenomena. In this work, we have fulfilled a robust room-temperature soft ferromagnetism together with a metallic characteristic based on a high quality SrRuO3-monolayer-based superlattice. Further examination on this short-range ferromagnetism has been carried out by synchrotron-related spectroscopy, where charge-transfer-induced antiferromagnetic coupling between partial Ru and Ti ions have been found. Although such local antiferromagnetic coupling would break long range ferromagnetic order, it simultaneously stabilize the localized intralayer ferromagnetic order in the SrRuO3 monolayers, which is confirmed by theoretical calculations. Our study not only represents a methodological advance of achieving fantastic magnetic properties in functional oxide monolayer, but is promising to unlock new opportunities for oxide-based spintronic devices toward room-temperature applications.

The ongoing quest for defect-free thin films systems that are apt for being used as spin filtering materials for spintronic applications did yet not deliver satisfying results regarding materials that would be up to the pertinent requirements. Using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Co-L2,3 and Fe-L2,3 absorption edges, we have investigated the magnetic properties of a nanostructured thin film with self-assembled CoFe2O4 nanopillars embedded in BiFeO3, the latter being a well-known system for its combined multiferroic and spintronic properties. In this BiFeO3-CoFe2O4 heterostructure we observed a significant XMCD signal at the Co-L2,3 edges which turns out to be the largest among the presently reported for Co ions at room temperature. A quantitative analysis of the Co-L2,3 spectra unveils that such a large Co-L2,3 XMCD signal stems from the impeccable fully inverted spinel ordering of the A- and B-sites in antiphase-free CoFe2O4 nanopillars. This twofold perfect CoFe2O4 ordering feature yields an unprecedented optimization within a multifunctional ferrimagnetic-multiferroic thin film system highly relevant for spintronic applications, also resulting in an equally unprecedented macroscopic magnetic moment for such material as compared to its pure form as well as to technologically relevant thin film compound systems.

A series of polycrystalline double perovskites SrLaBIrO6 (B = Ni, Mg, Zn) containing Ir5+ (5d4) has been synthesized by solid state reactions, and structural, magnetic and electronic properties were investigated. The isotypic fully ordered double perovskites crystallize in space group P21/n and show semiconducting behavior with estimated band gaps of approximately 0.2 eV for SrLaNiIrO6 and SrLaZnIrO6, and 0.4 eV for SrLaMgIrO6. SrLaNiIrO6 is an antiferromagnet with a Neel temperature of 74 K (eff = 3.3 B, W = -90 K) while SrLaMgIrO6 and SrLaZnIrO6 are weakly paramagnetic. All title compounds exhibit a temperature-independent contribution to the measured magnetic susceptibility which supports the notion for a van-Vleck-type response originating from the Ir5+ (5d4, Jeff = 0) ions.

A layered Sr2Co0.5Ir0.5O4 (S.G. I4/mmm) perovskite of the K2NiF4 structure type was synthesized as a single-phase sample. Neutron powder diffraction measurements revealed full site occupancy of oxygen atoms. The Co3+/Ir5+ valence states were evaluated by the combination of X-ray absorption and X-ray photoemission spectroscopy as well as by the magnetization measurements, hence confirming the difference to the parent compounds Sr2CoO4 and Sr2IrO4 with similar structures. The Co-K edge EXAFS studies indicated a large average Co-O distances of 1.967 A suggesting a high spin state of Co3+ ion in Sr2Co0.5Ir0.5O4. No long-range magnetic ordering down to 4 K was detected by neutron powder diffraction, probably hindered by the random distribution of Co and Ir cations in the Sr2Co0.5Ir0.5O4 structure. High-pressure synchrotron powder diffraction studies showed stability of the Sr2Co0.5Ir0.5O4 structure at least up to 27 GPa at room temperature. A maximum in the c/a ratio at 10 GPa together with an anomaly in the pressure dependence of the unit cell volume could be a sign of a change in the Co ions spin state under pressure.

We have studied the electronic structure of ${\mathrm{BaCoO}}_{3}$ using soft x-ray absorption spectroscopy at the Co ${L}_{2,3}$ and O $K$ edges, magnetic circular dichroism at the Co ${L}_{2,3}$ edges, and valence band hard x-ray photoelectron spectroscopy. The quantitative analysis of the spectra established that the Co ions are in the formal low-spin tetravalent $3{d}^{5}$ state and that the system is a negative charge transfer Mott insulator. The spin-orbit coupling also plays an important role for the magnetism of the system. At the same time, a trigonal crystal field is present with sufficient strength to bring the $3{d}^{5}$ ion away from the ${J}_{\mathrm{eff}}=1/2$ state. The sign of this crystal field is such that the ${a}_{1g}$ orbital is doubly occupied, explaining the absence of a Peierls transition in this system, which consists of chains of face-sharing ${\mathrm{CoO}}_{6}$ octahedra. Moreover, with one hole residing in ${e}_{g}^{\ensuremath{\pi}}$, the presence of an orbital moment and strong magnetocrystalline anisotropy can be understood. Yet we also infer that crystal fields with lower symmetry must be present to reproduce the measured orbital moment quantitatively, thereby suggesting the possibility for orbital ordering to occur in ${\mathrm{BaCoO}}_{3}$.

We report on our investigation on the magnetism of the iridate double perovskite ${\mathrm{Sr}}_{2}{\mathrm{CoIrO}}_{6}$, a nominally ${\mathrm{Ir}}^{5+}$ Van Vleck ${J}_{\mathrm{eff}}=0$ system. Using x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy at the Ir-${L}_{2,3}$ edges, we found a nearly zero orbital contribution to the magnetic moment and thus an apparent breakdown of the ${J}_{\mathrm{eff}}=0$ ground state. By carrying out also XAS and XMCD experiments at the Co-${L}_{2,3}$ edges and by performing detailed full atomic multiplet calculations to simulate all spectra, we discovered that the compound consists of about 90% ${\mathrm{Ir}}^{5+}$ (${J}_{\mathrm{eff}}=0$) and ${\mathrm{Co}}^{3+}$ ($S=2$) and 10% ${\mathrm{Ir}}^{6+}$ ($S=3/2$) and ${\mathrm{Co}}^{2+}$ ($S=3/2$). The magnetic signal of this minority ${\mathrm{Ir}}^{6+}$ component is almost equally as strong as that of the main ${\mathrm{Ir}}^{5+}$ component. We infer that there is a competition between the ${\mathrm{Ir}}^{5+}\ensuremath{-}{\mathrm{Co}}^{3+}$ and the ${\mathrm{Ir}}^{6+}\ensuremath{-}{\mathrm{Co}}^{2+}$ configurations in this stoichiometric compound.

Interfaces of ferroic oxides can show complex magnetic textures which have strong impact on spintronics devices. This has been demonstrated recently for interfaces with insulating antiferromagnets such as $\mathrm{BiFe}{\mathrm{O}}_{3}$. Here, noncollinear spin textures which can be switched in very low magnetic field are reported for conducting ferromagnetic bilayers of $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{SrRu}{\mathrm{O}}_{3}$ (LSMO-SRO). The magnetic order and switching are fundamentally different for bilayers coherently grown in reversed stacking sequence. The SRO top layer forms a persistent exchange spring which is antiferromagnetically coupled to LSMO and drives switching in low fields of a few milliteslas. Density functional theory reveals the crucial impact of the interface termination on the strength of Mn-Ru exchange coupling across the interface. The observation of an exchange spring agrees with ultrastrong coupling for the $\mathrm{Mn}{\mathrm{O}}_{2}/\mathrm{SrO}$ termination. Our results demonstrate low-field switching of noncollinear spin textures at an interface between conducting oxides, opening a pathway for manipulating and utilizing electron transport phenomena in controlled spin textures at oxide interfaces.

Motivated by the recent synthesis of Ba 2 CuO 3 + δ (BCO), a high temperature superconducting cuprate with putative d 3 z 2 − r 2 ground state symmetry, we investigated its electronic structure by means of Cu L 3 x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) at the Cu L 3 edge on a polycrystalline sample. We show that the XAS profile of BCO is characterised by two peaks associated to inequivalent Cu sites, and that its RIXS response features a single, sharp peak associated to crystal-field excitations. We argue that these observations are only partially compatible with the previously proposed crystal structure of BCO. Based on our spectroscopic results and on previously published powder diffraction measurements, we propose a crystalline structure characterized by two inequivalent Cu sites located at alternated planes along the c axis: nominally trivalent Cu(1) belonging to very short Cu-O chains, and divalent Cu(2) in the oxygen deficient CuO 1.5 planes. We also analyze the low-energy region of the RIXS spectra to estimate the magnitude of the magnetic interactions in BCO and find that in-plane nearest neighbor superexchange exceeds 120 meV, similarly to that of other layered cuprates. Although these results do not support the pure d 3 z 2 − r 2 ground state scenario, they hint at a significant departure from the common quasi-2D electronic structure of superconducting cuprates of pure d x 2 − y 2 symmetry.

Pb2FeOsO6 was prepared for the first time by using high-pressure and high-temperature synthesis techniques. This compound crystallizes into a B-site-ordered double-perovskite structure with cubic symmetry Fm3m, where the Fe and Os atoms are orderly distributed with a rock-salt-type manner. Structure refinement shows an Fe–Os antisite occupancy of about 16.6%. Structural analysis and X-ray absorption spectroscopy both demonstrate the charge combination to be Pb2Fe3+Os5+O6. A long-range ferrimagnetic transition is found to occur at about 280 K due to antiferromagnetic interactions between the adjacent Fe3+ and Os5+ spins with a straight (180°) Fe–O–Os bond angle, as confirmed by X-ray magnetic circular-dichroism measurements. First-principles theoretical calculations reveal the semiconducting behavior as well as the Fe3+(↑)Os5+(↓) antiferromagnetic coupling originating from the superexchange interactions between the half-filled 3d orbitals of Fe and t2g orbitals of Os.

The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO3 generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO3 material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis. With this we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii–Moriya interaction is parallel to the a axis. Furthermore, by fabricating a Co/BiFeO3 heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO3., The coupling of ferroelectric and antiferromagnetic order in BiFeO3 makes it appealing for applications however the presence of domain structure acts to undermine this potential. Here, the authors demonstrate BiFeO3 thin films with a single domain of electrical polarization and canted antiferromagnetic order.

An A- and B-site ordered quadruple perovskite oxide LaCu3Co2Re2O12 was synthesized at 9 GPa and 1323 K. The compound possesses a Pn-3 space group, where both A and B sites are orderly occupied by different cations with a nearly 100% degree of order. Bond valence sum calculations and x-ray absorption spectroscopy confirm the charge distribution to be LaCu2+3Co2+2Re5.5+2O12. A ferrimagnetic phase transition is found to occur around 150 K due to the Cu2+(↑)-Co2+(↑)-Re5.5+(↓) spin coupling found by x-ray magnetic circular dichroism at Cu-, Co-, and Re-L2,3 edges. The magnetoresistance effects as well as the first-principle calculations indicate the half-metallic nature for LaCu3Co2Re2O12 with a wider energy gap at the up-spin channel and a conducting band at the down-spin channel.

The conducting oxide ferromagnets SrRuO3 (SRO) and LaSr0.3MnO3 (LSMO) form a Ru exchange spring at a coherent low‐interdiffusion interface grown on TiO2‐terminated SrTiO3(STO)(001) substrates as SRO(d)/LSMO/STO(001) bilayers. Field‐ and temperature‐dependent magnetization data with systematically varied thickness d of SRO from 7 to 18 unit cells (uc) indicate a thickness of 10–14 uc of the exchange spring which governs magnetic switching and causes thickness‐dependent field‐cooling effects. Mn L3 edge X‐ray magnetic circular dichroism (XMCD) data reveal the dominating in‐plane orientation of interfacial spins. In low magnetic fields, noncoplanar, topologically nontrivial spin textures arise and can be switched, driven by the Zeeman energy of the LSMO layer.

We report a combined experimental and theoretical x-ray magnetic circular dichroism (XMCD) spectroscopy study at the Ir-${L}_{2,3}$ edges on the ${\mathrm{Ir}}^{5+}$ ions of the layered hybrid solid state oxide ${\mathrm{Sr}}_{2}{\mathrm{Co}}_{0.5}{\mathrm{Ir}}_{0.5}{\mathrm{O}}_{4}$ with the ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}$ structure. From theoretical simulation of the experimental Ir-${L}_{2,3}$ XMCD spectrum, we found a deviation from a pure ${J}_{\mathrm{eff}}=0$ ground state with an anisotropic orbital-to-spin moment ratio (${L}_{x}/2{S}_{x}=0.43$ and ${L}_{z}/2{S}_{z}=0.78$). This deviation is mainly due to multiplet interactions being not small compared to the cubic crystal field and due to the presence of a large tetragonal crystal field associated with the crystal structure. Nevertheless, our calculations show that the energy gap between the singlet ground state and the triplet excited state is still large and that the magnetic properties of the ${\mathrm{Ir}}^{5+}$ ions can be well described in terms of singlet Van Vleck paramagnetism.

We report on our investigation of the electronic structure of Ti2O3 using (hard) x-ray photoelectron and soft x-ray absorption spectroscopy. From the distinct satellite structures in the spectra, we have been able to establish unambiguously that the Ti-Ti c-axis dimer in the corundum crystal structure is electronically present and forms an a(1g)a(1g) molecular singlet in the low-temperature insulating phase. Upon heating, we observe a considerable spectral weight transfer to lower energies with orbital reconstruction. The insulator-metal transition may be viewed as a transition from a solid of isolated Ti-Ti molecules into a solid of electronically partially broken dimers, where the Ti ions acquire additional hopping in the a-b plane via the e(g)(pi) channel, the opening of which requires consideration of the multiplet structure of the on-site Coulomb interaction.

Here, we report the growth of centimeter-sized γ-CoV2O6 single crystals by the optical floating zone method which are suitable for neutron scattering experiments. Our floating zone grown single crystals have higher magnetic ordering temperatures of 7.8 K, much more clearly visible magnetization plateaus, and substantially enhanced saturation magnetizations compared to flux-grown single crystals, which is also important with regard to the presence of orbital moment contributions within these S = 3/2 systems. Our centimeter-sized single crystals grown by the optical floating zone technique open the way toward the measurement of the peculiar magnetic properties of this intriguing system by means of elastic and inelastic neutron scattering and have been characterized by X-ray and neutron diffraction measurements.

$\ensuremath{\alpha}$-RuCl${}_{3}$ is the most promising candidate for the long-sought materialization of the Kitaev model, where compasslike exchange interactions lead to a gapless spin liquid with emergent Majorana fermion excitations. Prerequisite for these expectations is that the symmetry-imposed noncubic crystal field is smaller compared to the spin-orbit coupling and does not perturb significantly the description of the electronic ground state in terms of the ${J}_{\text{eff}}$ = 1/2 state. Here, the authors combine polarization-dependent x-ray absorption spectroscopy, a technique that gives direct access to the crystal field of a material, and full multiplet calculations to determine the size and sign of the noncubic crystal-field splitting. The results demonstrate that the ``electronically cubic conditions'' and the ${J}_{\text{eff}}$ = 1/2 ground state for Ru in $\ensuremath{\alpha}$-RuCl${}_{3}$ are fulfilled.

We report on a combined soft x-ray absorption and magnetic circular dichroism (XMCD) study at the Co-${L}_{3,2}$ edge on the hybrid $3d/5d$ solid state oxide ${\mathrm{Sr}}_{2}{\mathrm{Co}}_{0.5}{\mathrm{Ir}}_{0.5}{\mathrm{O}}_{4}$ with ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}$ structure. Our data indicate unambiguously a pure high spin state $(S=2)$ for the ${\mathrm{Co}}^{3+}$ ($3{d}^{6}$) ions with a significant unquenched orbital moment ${L}_{z}/2{S}_{z}=0.25$ despite the sizable elongation of the ${\mathrm{CoO}}_{6}$ octahedra. Using quantitative model calculations based on parameters consistent with our spectra, we have investigated the stability of this high spin state with respect to the competing low spin and intermediate spin states.

We have investigated the electronic structure of ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ using core-to-core resonant inelastic x-ray scattering. The experimental spectra can be well reproduced using ab initio density functional theory based multiplet ligand field theory calculations, thereby validating these calculations. We found that the low-energy, effective Ir ${\mathrm{t}}_{2\mathrm{g}}$ orbitals are practically degenerate in their crystal-field energy. We uncovered that ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ and iridates in general are negative charge transfer systems with large covalency and a substantial oxygen ligand hole character in the Ir ${\mathrm{t}}_{2\mathrm{g}}$ Wannier orbitals. This has far reaching consequences, as not only the on-site crystal-field energies are determined by the long-range crystal structure, but, more significantly, magnetic exchange interactions will have long-range distance dependent anisotropies in the spin direction. These findings set constraints and show pathways for the design of ${d}^{5}$ materials that can host compasslike magnetic interactions.

We have carried out bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) measurements on in-situ cleaved and ex-situ polished SmB6 single crystals. Using the multiplet-structure in the Sm 3d core level spectra, we determined reliably that the valence of Sm in bulk SmB6 is close to 2.55 at ~5 K. Temperature dependent measurements revealed that the Sm valence gradually increases to 2.64 at 300 K. From a detailed line shape analysis we can clearly observe that not only the J=0 but also the J=1 state of the Sm 4f 6 configuration becomes occupied at elevated temperatures. Making use of the polarization dependence, we were able to identify and extract the Sm 4f spectral weight of the bulk material. Finally, we revealed that the oxidized or chemically damaged surface region of the ex-situ polished SmB6 single crystal is surprisingly thin, about 1 nm only., Comment: 11 pages, 8 figures

Pb

The crystal-field ground-state wave functions of the tetragonal, magnetically ordering Kondo lattice materials $\mathrm{Ce}M{\mathrm{Al}}_{4}{\mathrm{Si}}_{2}$ $(M=\text{Rh}$, Ir, and Pt) are determined with low-temperature linearly polarized soft-x-ray absorption spectroscopy, and estimates for the crystal-field splittings are given from the temperature evolution of the linear dichroism. Values for the dominant exchange field in the magnetically ordered phases can be obtained from fitting the influence of magnetic order on the linear dichroism. The direction of the required exchange field is $\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}c$ for the antiferromagnetic Rh and Ir compounds, with the corresponding strength of the order of ${\ensuremath{\lambda}}_{\text{ex}}\ensuremath{\approx}6\phantom{\rule{4pt}{0ex}}\text{meV}$ (65 K). Furthermore, the presence of Kondo screening in the Rh and Ir compound is demonstrated on the basis of the absorption due to ${f}^{0}$ in the initial state.

The second-order phase transition into a hidden order phase in URu$_2$Si$_2$ goes along with an order parameter which is still a mystery, despite 30 years of research. However, it is understood that the symmetry of the order parameter must be related to the symmetry of the low lying local electronic $f$-states. Here we present results of a novel spectroscopy, namely core-level non-resonant inelastic x-ray scattering (NIXS). This method allows for the measurement of local high-multipole excitations and it is bulk sensitive. The observed anisotropy of the scattering function unambiguously shows that the 5$f$ ground state wave function is composed mainly, but essentially not purely, of the $\Gamma_1$ with majority $J_z$ =$|4\rangle$ + $|-4\rangle$ and/or $\Gamma_2$ singlet states., Comment: 9 pages, 6 figures