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The ligand field (LF) of transition metal ions is a crucial factor in realizing the mechanism of novel physical and chemical properties. However, the low-crystallinity state, including the amorphous state, precludes the clarification of the electronic structural relationship of transition metal ions using crystallographic techniques, ultraviolet and infrared optical methods, and magnetometry. Here, we demonstrate that soft X-ray 2p → 3d core-level absorption spectroscopy (

Titanium disulfide TiS$_2$, which is a member of the layered transition-metal dichalcogenides with the 1T-CdI$_2$-type crystal structure, is known to exhibit a wide variety of magnetism through intercalating various kinds of transition-metal atoms of different concentrations. Among them, Fe-intercalated titanium disulfide Fe$_x$TiS$_2$ is known to be ferromagnetic with strong perpendicular magnetic anisotropy (PMA) and large coercive fields ($H_\text{c}$). In order to study the microscopic origin of the magnetism of this compound, we have performed X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements on single crystals of heavily intercalated Fe$_x$TiS$_2$ ($x\sim0.5$). The grown single crystals showed a strong PMA with a large $H_\text{c}$ of $\mu_0H_\text{c} \simeq 1.0\ \text{T}$. XAS and XMCD spectra showed that Fe is fully in the valence states of 2+ and that Ti is in an itinerant electronic state, indicating electron transfer from the intercalated Fe atoms to the host TiS$_2$ bands. The Fe$^{2+}$ ions were shown to have a large orbital magnetic moment of $\simeq 0.59\ \mu_\text{B}\text{/Fe}$, to which, combined with the spin-orbit interaction and the trigonal crystal field, we attribute the strong magnetic anisotropy of Fe$_x$TiS$_2$., Comment: 24 pages, 8 figures

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.

Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO3 thin film at ambient temperature via laser illumination. Phase-field simulations indicate that a light-driven flexoelectric effect allows the targeted formation of ordered domains. We also achieved precise sequential laser writing and erasure of different domain patterns, which demonstrates a deterministic optical control of multiferroicity at room temperature. As ferroic orders directly influence susceptibility and conductivity in complex materials, our results not only shed light on the optical control of multiple functionalities, but also suggest possible developments for optoelectronics and related applications.

The electronic and magnetic structure of orthorhombic (o-) YMn0.5Fe0.5O3 (YMFO) epitaxial film (space group Pbnm) deposited on the YAlO3 (010) substrate have been investigated using linear polarization-dependent x-ray absorption spectroscopy and magnetization measurements. The magnetic-ordering temperature of around 280 K is observed in o-YMFO film. The x-ray absorption spectra at the Fe-K and the Mn-K edges indicate the existence of anisotropic crystal field in o-YMFO film, with the longest and shortest Fe–O and Mn–O bonds tend to align with the crystallographic b- and a-axis, respectively, whereas the medium Fe(Mn)–O bond is aligned with the c-axis. The experimental x-ray magnetic linear dichroism at the Fe-L2 edges demonstrate an unusual single antiferromagnetic axis of Fe3+ ions below magnetic-ordering temperature, while a multi antiferromagnetic axis is generally observed in o-RFeO3 (R = rare earth) thin films. Our configuration-interaction cluster calculations also reveal that the single antiferromagnetic axis of the Fe sublattice is aligned with the b-axis in o-YMFO film, whereas it is directed along the a-axis in the bulk o-YFeO3.

Using soft x-ray absorption spectroscopy we were able to determine unambiguously the charge and spin states of the transition metal ions in stoichiometric $\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ and $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$. The trivalent and low-spin nature of both the Cu and Co ions in $\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ makes this correlated system to be effectively a nonmagnetic band semiconductor. The substitution of Y by Ca produces formally tetravalent Co ions but the doped holes are primarily on the oxygen ligands. Concerning the spin degrees of freedom, the trivalent Co ions in $\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ remain low spin upon the Y-Ca substitution, very much unlike the ${\mathrm{La}}_{1\text{\ensuremath{-}}x}{\mathrm{Sr}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$ system. The tetravalent Co ions in $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ are interestingly also in the low-spin state, which then explains the good electrical conductivity of $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ since charge exchange between neighboring ${\mathrm{Co}}^{3+}$ and ${\mathrm{Co}}^{4+}$ ions will not be hampered by the spin-blockade mechanism that otherwise would be in effect if the ${\mathrm{Co}}^{4+}$ and ${\mathrm{Co}}^{3+}$ spin quantum numbers were to differ by more than one-half. We infer that the stability of the Co low-spin state is related to the very short Co-O bond lengths.

SmO thin film is a new Kondo system showing a resistivity upturn around 10 K and was theoretically proposed to have a topologically nontrivial band structure. We perform hard x-ray and soft x-ray photoemission spectroscopy to elucidate the electronic structure of SmO. From the Sm $3d$ core-level spectra, we estimate the valence of Sm to be $\ensuremath{\sim}2.96$, proving that the Sm has a mixed valence. The valence-band photoemission spectra exhibit a clear Fermi edge originating from the Sm $5d$-derived band. The present finding is consistent with the theory suggesting a possible topological state in SmO and show that rare-earth monoxides or their heterostructures can be a new playground for the interplay of strong electron correlation and spin-orbit coupling.

The Mn3WO6 oxide, prepared by a solid-state reaction at ambient pressure, is found to crystallize at room temperature in the centrosymmetric R3 trigonal structure of Mg3TeO6. By X-ray absorption s...

The employment of flexible muscovite substrates has given us the feasibility of applying strain to heterostructures dynamically by mechanical bending. In this study, this novel approach is utilized to investigate strain effects on the exchange coupling in ferromagnetic Co and anti-ferromagnetic CoO (Co/CoO) bilayers. Two different Co/CoO bilayer heterostructures were grown on muscovite substrates by oxide molecular beam epitaxy, with the CoO layer being purely (111)- and (100)-oriented. The strain-dependent exchange coupling effect can only be observed on Co/CoO(100)/mica but not on Co/CoO(111)/mica. The origin of this phenomenon is attributed to the anisotropic spin re-orientation induced by mechanical bending. The strain-dependent magnetic anisotropy of the bilayers determined by anisotropic magnetoresistance measurements confirms this conjecture. This study elucidates the fundamental understanding of how magnetic exchange coupling can be tuned by externally applied strain via mechanical bending and, hence, provides a novel approach for implementing flexible spintronic devices.

Perpendicular magnetic anisotropy of the new ferromagnetic semiconductor (Ba,K)(Zn,Mn)$_{2}$As$_{2}$ is studied by angle-dependent x-ray magnetic circular dichroism measurements. The large magnetic anisotropy with the anisotropy field of 0.85 T is deduced by fitting the Stoner-Wohlfarth model to the magnetic-field-angle dependence of the projected magnetic moment. Transverse XMCD spectra highlights the anisotropic distribution of Mn 3$d$ electrons, where the $d_{xz}$ and $d_{yz}$ orbitals are less populated than the $d_{xy}$ state because of the $D_{2d}$ splitting arising from the elongated MnAs$_{4}$ tetrahedra. It is suggested that the magnetic anisotropy originates from the degeneracy lifting of $p$-$d_{xz}$, $d_{yz}$ hybridized states at the Fermi level and resulting energy gain due to spin-orbit coupling when spins are aligned along the $z$ direction.

Fundamental understanding of interfacial magnetic properties in ferromagnetic heterostructures is essential to utilize ferromagnetic materials for spintronic device applications. In this paper, we investigate the interfacial magnetic and electronic structures of epitaxial single-crystalline LaAlO$_3$ (LAO)/La$_{0.6}$Sr$_{0.4}$MnO$_3$ (LSMO)/Nb:SrTiO$_3$ (Nb:STO) heterostructures with varying LSMO-layer thickness, in which the magnetic anisotropy strongly changes depending on the LSMO thickness due to the delicate balance between the strains originating from both the Nb:STO and LAO layers, using x-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy (PES). We successfully detect the clear change of the magnetic behavior of the Mn ions concomitant with the thickness-dependent metal-insulator transition (MIT). Our results suggest that double-exchange interaction induces the ferromagnetism in the metallic LSMO film under tensile strain caused by the SrTiO$_3$ substrate, while superexchange interaction determines the magnetic behavior in the insulating LSMO film under compressive strain originating from the top LAO layer. Based on those findings, the formation of a magnetic dead layer near the LAO/LSMO interface is attributed to competition between the superexchange interaction via Mn 3$d_{3z^2-r^2}$ orbitals under compressive strain and the double-exchange interaction via the 3$d_{x^2-y^2}$ orbitals., Comment: 20 pages, 6 figures

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.

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.

We have revealed that anisotropic 4f charge distributions caused by the crystalline electric field are responsible for linear dichroism (LD) in 3d core-level photoemission spectra of rare earth compounds. Indeed, we have successfully observed the intrinsic LD for cubic YbB 12 and tetragonal SmCu 2 Si 2 . We have also performed polarization-dependent 4f photoemission in a valence-band region. The observed LDs in the experimental 4f spectra are reduced from those predicted from the theoretical simulations for the localized ions.

The role of transition-metal d and ligand p hybridization continues to be of immense interest in Li-ion battery cathode, and yet it is still poorly understood. Using combined experimental and theoretical soft X-ray absorption spectroscopic study and density functional theory calculation, we investigated the fundamental electronic structure of the high-voltage spinel LiNixMn2–xO4. An oxygen-participating charge rebalance between manganese and nickel ions was found; that is, the content of O 2p holes close to the Fermi level increases along with the increasing Ni content. Moreover, these unstable oxygen holes primarily congregate around the redox active dopants. The underlying mechanism accounting for this charge-compensated occurrence is the reverse of two bonding levels when manganese ions are oxidized from +3 to +4 states. On the basis of these new findings, we further exposed the role of oxygen in electrochemical performance. First, oxygen ions afford the charge variation together with the cations durin...

We report on a detailed experimental and theoretical study of the electronic structure of NiO. The charge-transfer nature of the band gap as well as the intricate interplay between local electronic correlations and band formation makes NiO to be a challenging case for a quantitative ab-initio modeling of its electronic structure. To reproduce the compensated-spin character of the first ionization state and the state created by hole doping requires a reliable determination of the charge transfer energy Δ relative to the Hubbard U. Furthermore, the presence of non-local screening processes makes it necessary to go beyond single-site many body approaches to explain the valence band spectrum.

A trap-density-based compact model of dynamic metal-oxide semiconductor field-effect transistor degradation due to hot electrons is reported, for which model parameters are extractable from measured 1/ ${f}$ noise properties. It is observed that the deep trap-state increase is dominant for the degradation and approaches its maximum under long accelerated-stress duration. A key modeling concept is the explicit inclusion of the extracted stress-condition-dependent trap density in the Poisson equation, which is solved iteratively. The developed model correctly predicts actual dynamic degradation of the measured I-V characteristics, that is, trap density increase during stress application, without the disadvantage of longer simulation times. The reported model can automatically reproduce not only the threshold-voltage shift, but also the degradation of the complete ${I}$ – ${V}$ characteristics and all other observable effects caused by the carrier trapping, without any additional model-parameter fitting for each of these effects.

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 have probed the crystalline electric-field ground states of pure $|J=7/2,{J}_{z}=\ifmmode\pm\else\textpm\fi{}5/2⟩$ as well as the anisotropic $c\text{\ensuremath{-}}f$ hybridization in both valence fluctuating systems $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-${\mathrm{YbAlB}}_{4}$ by linear polarization dependence of angle-resolved core level photoemission spectroscopy. Interestingly, the small but distinct difference between $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-${\mathrm{YbAlB}}_{4}$ was found in the polar angle dependence of linear dichroism, indicating the difference in the anisotropy of $c\text{\ensuremath{-}}f$ hybridization, which may be a key to understanding a heavy Fermi liquid state in $\ensuremath{\alpha}$-${\mathrm{YbAlB}}_{4}$ and a quantum critical state in $\ensuremath{\beta}$-${\mathrm{YbAlB}}_{4}$.

We investigate and compare the electronic structure of a bulk single crystal of ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ garnet [YIG, a high-${T}_{C}$ (= 560 K) ferrimagnet] with that of an epitaxial ultrathin (3.3 nm) film of YIG with a reduced ferrimagnetic temperature ${T}_{C}=380\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, using bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES), x-ray absorption spectroscopy (XAS), and x-ray magnetic circular dichroism (XMCD). The Fe $2p$ HAXPES spectrum of the bulk single crystal exhibits a purely trivalent ${\mathrm{Fe}}^{3+}$ state for octahedral and tetrahedral sites. The Fe $3s$ spectrum shows a clear splitting which allows us to estimate the on-site Fe $3s\text{\ensuremath{-}}3d$ exchange interaction energy. The valence band HAXPES spectrum shows Fe $3d$, O $2p$, and Fe $4s$ derived features and a band gap of $\ensuremath{\sim}2.3\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ in the occupied density of states, consistent with the known optical band gap of $\ensuremath{\sim}2.7\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. Fe $L$-edge XAS identifies the octahedral ${\mathrm{Fe}}^{3+}$ and tetrahedral ${\mathrm{Fe}}^{3+}$ site features. XMCD spectra at the Fe ${L}_{2,3}$ edges show that bulk single-crystal YIG exhibits antiferromagnetic coupling between the octahedral- and tetrahedral-site spins. The calculated Fe $2p$ HAXPES, Fe $L$-edge XAS, and XMCD spectra using full multiplet cluster calculations match well with the experimental results and confirm the full local spin moments. In contrast, HAXPES, XAS, and XMCD of the Pt/YIG (3.3 nm) ultrathin epitaxial film grown by a pulsed laser deposition method show a finite ${\mathrm{Fe}}^{2+}$ contribution and a reduced ${\mathrm{Fe}}^{3+}$ local spin moment. The ${\mathrm{Fe}}^{2+}$ state is attributed to a combination of oxygen deficiency and charge transfer effects from the Pt capping layer to the ultrathin film. However, the conserved XMCD spectral shape for the ultrathin film indicates that the 3.3-nm epitaxial film is genuinely ferrimagnetic, in contrast to recent studies on films grown by radio-frequency magnetron sputtering which have shown a magnetic dead layer of $\ensuremath{\sim}6$ nm. The presence of ${\mathrm{Fe}}^{2+}$ and the reduced local spin moment in the epitaxial ultrathin film lead to a reduced Curie temperature, quantitatively consistent with well-known mean-field theory. The results establish a coupling of the local Fe spin moments, valency, and long-range magnetic ordering temperature in bulk single crystal and epitaxial ultrathin-film YIG.

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.

We report the core-level photoemission study of cubic PrBe13, PrIr2Zn20 and PrB6 using linearly polarized hard X-ray. We have successfully observed linear dichroism (LD) in Pr3+ 3d core-level photoemission spectra reflecting the 4f ground-state symmetry for all the compounds. The observed LDs and polarization-dependent spectra are reproduced by ionic-model calculations including the full multiplet theory and the local crystalline electric field (CEF) splitting. We have confirmed that LDs in Pr3+ 3d core-level photoemission spectra are able to determine unambiguously the Pr3+ 4f ground-state symmetry.

We have probed the crystalline electric-field ground states of pure |J=7/2,J_{z}=±5/2⟩ as well as the anisotropic c-f hybridization in both valence fluctuating systems α- and β-YbAlB_{4} by linear polarization dependence of angle-resolved core level photoemission spectroscopy. Interestingly, the small but distinct difference between α- and β-YbAlB_{4} was found in the polar angle dependence of linear dichroism, indicating the difference in the anisotropy of c-f hybridization, which may be a key to understanding a heavy Fermi liquid state in α-YbAlB_{4} and a quantum critical state in β-YbAlB_{4}.

We present a detailed study on the $4f$ ground-state symmetry of the pressure-induced superconductor ${\mathrm{CeCu}}_{2}{\mathrm{Ge}}_{2}$ probed by soft x-ray absorption and hard x-ray photoemission spectroscopy. The revised Ce $4f$ ground states are determined as $|{\mathrm{\ensuremath{\Gamma}}}_{7}\ensuremath{\rangle}=\sqrt{0.45}|{J}_{z}=\ifmmode\pm\else\textpm\fi{}\frac{5}{2}\ensuremath{\rangle}\ensuremath{-}\sqrt{0.55}|\ensuremath{\mp}\frac{3}{2}\ensuremath{\rangle}$ with $\mathrm{\ensuremath{\Sigma}}$-type in-plane rotational symmetry. This gives an in-plane magnetic moment consistent with the antiferromagnetic moment as reported in neutron measurements. Since the in-plane symmetry is the same as that for the superconductor ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$, we propose that the charge distribution along the $c$ axis plays an essential role in driving the system into a superconducting phase.

Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO3 and EuTiO3. Despite this critical need, there are few studies on the strain evolution of magnetic order in BiFeO3 films. Here, in (110)-oriented BiFeO3 films, we reveal that while the polarization structure remains relatively unaffected, strain can continuously tune the orientation of the antiferromagnetic-spin axis across a wide angular space, resulting in an unexpected deviation of the classical perpendicular relationship between the antiferromagnetic axis and the polarization. Calculations suggest that this evolution arises from a competition between the Dzyaloshinskii–Moriya interaction and single-ion anisotropy wherein the former dominates at small strains and the two are comparable at large strains. Finally, strong coupling between the BiFeO3 and the ferromagnet Co0.9Fe0.1 exists such that the magnetic anisotropy of the ferromagnet can be effectively controlled by engineering the orientation of the antiferromagnetic-spin axis.

Recently synthesized Rh-Ni trinuclear complexes hexacoordinated with sulfur ions, 3-aminopropanethiolate (apt) metalloligand [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$ ($n$ = 2, 3, 4), are found to be chemically interconvertible between the nominal Ni$^{2+}$ and Ni$^{4+}$ states. In order to clarify the origins of their interconvertible nature and the stability of such a high oxidation state as the tetravalency from the physical point of view, we have systematically investigated the local 3$d$ electronic structures of [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$ by means of soft X-ray core-level absorption spectroscopy (XAS). The experimental data have been reproduced by the single-site configuration-interaction cluster-model simulations, which indicate that the charge-transferred configurations are more stable than the nominal $d$-electron-number configuration for $n=3,4$ leading to the prominent charge-transfer effects. These are also supported by S $K$-edge XAS of [Ni{Rh(apt)$_{3}$}$_{2}$](NO$_{3}$)$_{n}$. Our results imply that the found charge-transfer effects have a key role to realize the interconvertible nature as well as the stability of the high oxidization state of the Ni ions., Comment: 16 pages, 4 figures

Yb$_2$Si$_2$Al may be a prototype for exploring different aspects of the Shastry-Sutherland lattice, formed by planes of orthogonally coupled Yb ions. Measurements of the magnetic susceptibility find incoherently fluctuating Yb$^{3+}$ moments coexisting with a weakly correlated metallic state that is confirmed by measurements of the electrical resistivity. Increasing signs of Kondo coherence are found with decreasing temperature, including an enhanced Sommerfeld coefficient and Kadowaki-Woods ratio that signal that the metallic state found at the lowest temperatures is a Fermi liquid where correlations have become significantly stronger. A pronounced peak in the electronic and magnetic specific heat indicates that the coupling of the Yb moments to the conduction electrons leads to an effective Kondo temperature that is approximately 30 K. The valence of Yb$_2$Si$_2$Al has been investigated with electron spectroscopy methods. Yb$_2$Si$_2$Al is found to be strongly intermediate valent ($v_F=2.68(2)$ at 80 K). Taken together, these experimental data are consistent with a scenario where a coherent Kondo lattice forms in Yb$_2$Si$_2$Al from an incoherently fluctuating ensemble of Yb moments with incomplete Kondo compensation, and strong intermediate valence character., Submitted to Physical Review B

Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO

We have investigated the orbital states of the orbital-glassy (short-range orbital ordered) spinel vanadate Co$_{1.21}$V$_{1.79}$O$_{4}$ using x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and subsequent configuration-interaction cluster-model calculation. From the sign of the XMCD spectra, it was found that the spin magnetic moment of the Co ion is aligned parallel to the applied magnetic field and that of the V ion anti-parallel to it, consistent with neutron scattering studies. It was revealed that the excess Co ions at the octahedral site take the trivalent low-spin state, and induce a random potential to the V sublattice. The orbital magnetic moment of the V ion is small although finite, suggesting that the ordered orbitals mainly consists of real-number orbitals., 7 pages, 6 figures

$B$-site ordered thin films of double perovskite ${\mathrm{Sr}}_{2}{\mathrm{CoIrO}}_{6}$ were epitaxially grown by a metalorganic aerosol deposition technique on various substrates, actuating different strain states. X-ray diffraction, transmission electron microscopy, and polarized far-field Raman spectroscopy confirm the strained epitaxial growth on all used substrates. Polarization-dependent Co ${L}_{2,3}$ x-ray absorption spectroscopy reveals a change of the magnetic easy axis of the antiferromagnetically ordered (high-spin) ${\mathrm{Co}}^{3+}$ sublattice within the strain series. By reversing the applied strain direction from tensile to compressive, the easy axis changes abruptly from in-plane to out-of-plane orientation. The low-temperature magnetoresistance changes its sign respectively and is described by a combination of weak antilocalization and anisotropic magnetoresistance effects.

Here we present linear and circular polarized soft x-ray absorption spectroscopy (XAS) data at the Ce $M_{4,5}$ edges of the electron (Ir) and hole-doped (Re) Kondo semiconductor CeOs$_2$Al$_{10}$. Both substitutions have a strong impact on the unusual high N$\acute{e}$el temperature, $T_N$=28.5\,K, and also the direction of the ordered moment in case of Ir. The substitution dependence of the linear dichroism is weak thus validating the crystal-field description of CeOs$_2$Al$_{10}$ being representative for the Re and Ir substituted compounds. The impact of electron- and hole-doping on the hybridization between conduction and 4$f$ electrons is related to the amount of $f^0$ in the ground state and reduction of x-ray magnetic circular dichroism. A relationship of $cf$-hybridization strength and enhanced $T_N$ is discussed. The direction and doping dependence of the circular dichroism is in agreement with strong Kondo screening along the crystallographic $a$ direction.

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.

Magnetic anisotropies of ferromagnetic thin films are induced by epitaxial strain from the substrate via strain-induced anisotropy in the orbital magnetic moment and that in the spatial distribution of spin-polarized electrons. However, the preferential orbital occupation in ferromagnetic metallic La$_{1-x}$Sr$_x$MnO$_3$ (LSMO) thin films studied by x-ray linear dichroism (XLD) has always been found out-of-plane for both tensile and compressive epitaxial strain and hence irrespective of the magnetic anisotropy. In order to resolve this mystery, we directly probed the preferential orbital occupation of spin-polarized electrons in LSMO thin films under strain by angle-dependent x-ray magnetic circular dichroism (XMCD). Anisotropy of the spin-density distribution was found to be in-plane for the tensile strain and out-of-plane for the compressive strain, consistent with the observed magnetic anisotropy. The ubiquitous out-of-plane preferential orbital occupation seen by XLD is attributed to the occupation of both spin-up and spin-down out-of-plane orbitals in the surface magnetic dead layer., Comment: 20 pages, 4 figures

We have studied the electronic structure of ferrimagnetic ${\mathrm{Mn}}_{2}\mathrm{VAl}$ single crystals by means of soft x-ray absorption spectroscopy (XAS), x-ray absorption magnetic circular dichroism (XMCD), and resonant soft x-ray inelastic scattering (RIXS). We have successfully observed the XMCD signals for all the constituent elements. The Mn ${L}_{2,3}$ XAS and XMCD spectra are reproduced by spectral simulations based on density-functional theory, indicating the itinerant character of the Mn $3d$ states. On the other hand, the V $3d$ electrons are rather localized since the ionic model can qualitatively explain the V ${L}_{2,3}$ XAS and XMCD spectra. This picture is consistent with local $dd$ excitations revealed by the V ${L}_{3}$ RIXS.

$\ensuremath{\alpha}$-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 present linear polarization-dependent soft x-ray absorption spectroscopy data at the Ce $M_{4,5}$ edges of Cd and Sn doped CeCoIn$_5$. The 4$f$ ground state wave functions have been determined for their superconducting, antiferromagnetic and paramagnetic ground states. The absence of changes in the wave functions in CeCo(In$_{1-x}$Cd$_x$)$_5$ suggests the 4$f$\,--\,conduction electron ($cf$) hybridization is not affected by globally Cd doping, thus supporting the interpretation of magnetic droplets nucleating long range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in CeCo(In$_{1-y}$Sn$_y$)$_5$ compresses the 4$f$ orbitals into the tetragonal plane of these materials, suggesting enhanced $cf$ hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the 4$f$ wave functions are a very sensitive probe of small changes in the hybridization of 4$f$ and conduction electrons, even conveying information about direction dependencies., 6 pages, 4 figures

Epitaxial $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}/\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ bilayers are expected to be highly efficient spin injectors into Si owing to the spin filter effect of $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$. To exploit the full potential of this system, understanding the microscopic origin of magnetically dead layers at the $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}/\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ interface is necessary. In this paper, we study the cation distribution, electronic structures, and the magnetic properties of $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}(111)$ layers with various thicknesses (thickness $d=1.4$, 2.3, 4, and 11 nm) in the epitaxial $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}(111)/\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}(111)/\mathrm{Si}(111)$ structures using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) combined with cluster-model calculation. The magnetization of $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ measured by XMCD gradually decreases with decreasing thickness $d$, and finally, a magnetically dead layer is clearly detected at $d=1.4\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$. The magnetically dead layer has frustration of magnetic interactions, which is revealed from comparison between the magnetizations at 300 and 6 K. From analysis using configuration-interaction cluster-model calculation, the decrease of $d$ leads to a decrease in the inverse-to-normal spinel structure ratio and also a decrease in the average valence of Fe at the octahedral sites. These results strongly indicate that the magnetically dead layer at the $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}/\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ interface originates from various complex networks of superexchange interactions through the change in the cation distribution and electronic structure. Furthermore, from comparison of the magnetic properties between $d=1.4$ and 2.3 nm, it is found that the ferrimagnetic order of the magnetically dead layer at the $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}/\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ interface is partially restored by increasing the thickness from $d=1.4$ to 2.3 nm.

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.