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Band-gap engineering is one of the fundamental techniques in semiconductor technology and also applicable in next generation spintronics using the spin degree of freedom. To fully utilize the spintronic materials, it is essential to optimize the spin-dependent electronic structures in the operando conditions by applying magnetic and/or electric fields. Here we present an advanced spectroscopic technique to probe the spin-polarized electronic structures by using magnetic circular dichroism (MCD) in resonant inelastic soft X-ray scattering (RIXS) under an external magnetic field. Thanks to the spin-selective dipole-allowed transitions in RIXS-MCD, we have successfully demonstrated the direct evidence of the perfectly spin-polarized electronic structures for the prototypical halfmetallic Heusller alloy $$\hbox {Co}_2\hbox {MnSi}$$ Co 2 MnSi . RIXS-MCD is a promising tool to probe the spin-dependent carriers and band-gap induced in the buried magnetic layers in an element specific way under the operando conditions.

Heusler alloys are a material class exhibiting various magnetic properties, including antiferromagnetism. A typical application of antiferromagnets is exchange bias that is a shift of the magnetization curve observed in a layered structure consisting of antiferromagnetic and ferromagnetic films. In this study, a layered sample consisting of a Heusler alloy, Mn2VAl and a ferromagnet, Fe, is selected as a material system exhibiting exchange bias. Although the fully ordered Mn2VAl is known as a ferrimagnet, with an optimum fabrication condition for the Mn2VAl layer, the Mn2VAl/Fe layered structure exhibits exchange bias. The appearance of the antiferromagnetic property in the Mn2VAl is remarkable, however, the details have been unclear. To clarify the microscopic aspects on the crystal structures and magnetic moments around the Mn2VAl/Fe interface, cross-sectional scanning transmission electron microscope (STEM) observation, and synchrotron soft X-ray magnetic circular dichroism (XMCD) measurements were employed. The high-angle annular dark-field STEM images demonstrated clusters of Mn2VAl with the L21 phase distributed only around the interface to the Fe layer in the sample showing the exchange bias. Furthermore, antiferromagnetic coupling between the Mn- and Fe-moments were observed in element-specific hysteresis loops measured using the XMCD. The locally ordered L21 phase and antiferromagnetic Mn-moments in the Mn2VAl were suggested as important factors for the exchange bias.

The discoveries of intrinsic ferromagnetism in atomically-thin van der Waals crystals have opened up a new research field enabling fundamental studies on magnetism at two-dimensional (2D) limit as well as development of magnetic van der Waals heterostructures. To date, a variety of 2D ferromagnetism has been explored mainly by mechanically exfoliating 'originally ferromagnetic (FM)' van der Waals crystals, while bottom-up approach by thin film growth technique has demonstrated emergent 2D ferromagnetism in a variety of 'originally non-FM' van der Waals materials. Here we demonstrate that V5Se8 epitaxial thin films grown by molecular-beam epitaxy (MBE) exhibit emergent 2D ferromagnetism with intrinsic spin polarization of the V 3d electrons despite that the bulk counterpart is 'originally antiferromagnetic (AFM)'. Moreover, thickness-dependence measurements reveal that this newly-developed 2D ferromagnet could be classified as an itinerant 2D Heisenberg ferromagnet with weak magnetic anisotropy, broadening a lineup of 2D magnets to those potentially beneficial for future spintronics applications.

The valence state of UTe$_2$ was studied by core-level photoelectron spectroscopy. The main peak position of the U $4f$ core-level spectrum of UTe$_2$ coincides with that of UB$_2$, which is an itinerant compound with a nearly $5f^3$ configuration. However, the main peak of UTe$_2$ is broader than that of UB$_2$, and satellite structures are observed in the higher binding energy side of the main peak, which are characteristics of mixed-valence uranium compounds. These results suggest that the U 5$f$ state in UTe$_2$ is in a mixed valence state with a dominant contribution from the itinerant $5f^3$ configuration., accepted to J. Phys. Soc. Jpn. (2021)

Magnetic transition metal dichalcogenide (TMD) films have recently emerged as promising candidates in hosting novel magnetic phases relevant to next-generation spintronic devices. However, systematic control of the magnetization orientation, or anisotropy, and its thermal stability characterized by Curie temperature $({T}_{\mathrm{C}})$, remains to be achieved in such films. Here we present self-intercalated epitaxial ${\mathrm{Cr}}_{1+\ensuremath{\delta}}{\mathrm{Te}}_{2}$ films as a platform for achieving systematic/smooth magnetic tailoring in TMD films. Using a molecular-beam epitaxy based technique, we have realized epitaxial ${\mathrm{Cr}}_{1+\ensuremath{\delta}}{\mathrm{Te}}_{2}$ films with smoothly tunable \ensuremath{\delta} over a wide range (0.33--0.82), while maintaining NiAs-type crystal structure. With increasing \ensuremath{\delta}, we found monotonic enhancement of ${T}_{\mathrm{C}}$ from 160 to 350 K, and the rotation of magnetic anisotropy from out-of-plane to in-plane easy-axis configuration for fixed film thickness. Contributions from conventional dipolar and orbital moment terms are insufficient to explain the observed evolution of magnetic behavior with \ensuremath{\delta}. Instead, ab initio calculations suggest that the emergence of antiferromagnetic interactions with \ensuremath{\delta}, and its interplay with conventional ferromagnetism, may play a key role in the observed trends. This demonstration of tunable ${T}_{\mathrm{C}}$ and magnetic anisotropy across room temperature in TMD films paves the way for engineering different magnetic phases for spintronic applications.

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy were applied at the Ge (Ga) ${L}_{2,3}$ edge to unravel the spin-resolved unoccupied electronic states of ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Ge}$ (Ga). Complicated spectral features were observed in both XAS and XMCD spectra. For their interpretation, we compared the experimental XAS and XMCD spectra with the calculated Ge (Ga) $4s$ and $4d$ orbital partial density of states. The comparison enabled a qualitative explanation of the XMCD spectra as the difference between the majority- and minority-spin unoccupied density of states summed over the $4s$ and $4d$ orbitals. Our finding provides a new approach to uncover the spin-split partial density of states above the Fermi level.

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

We investigated the magnetic properties of multiferroic hexagonal ErFeO3 thin films by using x-ray magnetic circular dichroism (XMCD) and synchrotron Mössbauer spectroscopy. In order to reveal the element-specific magnetic properties, temperature-dependent XMCD experiments were conducted at the Fe L 2,3 and Er M 4,5-edges. Apparent magnetic hysteresis loops appear for both ions below the Néel temperature, which suggests the existence of ferromagnetism. The temperature evolutions of the coercive field and spontaneous magnetization for both ions show similar behavior. These results indicate that Fe ions influence the magnetism of Er ions. Our results deepen the understanding of the physical properties of hexagonal rare-earth ferrite system.

The electronic structure of the unconventional superconductor UTe$_2$ was studied by resonant photoelectron spectroscopy (RPES) and angle-resolved photoelectron spectroscopy (ARPES) with soft X-ray synchrotron radiation. The partial $\mathrm{U}~5f$ density of states of UTe$_2$ were imaged by the $\mathrm{U}~4d$--$5f$ RPES and it was found that the $\mathrm{U}~5f$ state has an itinerant character, but there exists an incoherent peak due to the strong electron correlation effects. Furthermore, an anomalous admixture of the $\mathrm{U}~5f$ states into the $\mathrm{Te}~5p$ bands was observed at a higher binding energy, which cannot be explained by band structure calculations. On the other hand, the band structure of UTe$_2$ was obtained by ARPES and its overall band structure were mostly explained by band structure calculations. These results suggest that the $\mathrm{U}~5f$ states of UTe$_2$ have itinerant but strongly-correlated nature with enhanced hybridization with the $\mathrm{Te}~5p$ states., 5 pages, 7 figures

The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature ${T}_{\mathrm{C}}$ can exceed room temperature, were investigated by means of x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable $3{d}^{6}$ contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe $3d$ electrons, whereas the former indicates their itinerant nature. It was also found that the Fe $3d$ states have a finite contribution to the density of states at the Fermi energy. These states, presumably consisting of majority-spin $p\text{\ensuremath{-}}d$ hybridized states or minority-spin $e$ states, would be responsible for the ferromagnetic order in this material.

Ferromagnetic topological insulators have emerged as a promising platform for quantum anomalous Hall (QAH) effect with a dissipationless edge transport. However, the observation of QAH effect has so far been restricted to extremely low temperatures. We investigate the microscopic origin of ferromagnetism coupled with topological insulators in vanadium-doped (Sb, Bi)(2)Te-3 employing the x-ray magnetic circular dichroism, angle-resolved two-photon photoemission spectroscopy, combined with first-principles calculations. We found a negative spin polarization, and thus an antiparallel magnetic moment at the Te site with respect to that of the vanadium dopants, which plays the key role in the ferromagnetic order. We ascribe it to the hybridization between Te p and V d majority spin states at the Fermi energy (E-F), being supported by a Zener-type p-d exchange interaction scenario. The substitution of Bi at the Sb site suppresses the bulk ferromagnetism by introducing extra electron carriers in the majority spin channel of Te p states that compensates the antiparallel magnetic moment on the Te site. Our findings reveal important clues to designing magnetic topological insulators with higher Curie temperature that work under ambient conditions.

A new kind of magnetically-doped antiferromagnetic (AFM) topological insulators (TIs) with stoichiometry Bi1.09Gd0.06Sb0.85Te3 has been studied by angle-resolved photoemission spectroscopy (ARPES), superconducting magnetometry (SQUID) and X-ray magnetic circular dichroism (XMCD) with analysis of its electronic structure and surface-derived magnetic properties at different temperatures. This TI is characterized by the location of the Dirac gap at the Fermi level (EF) and a bulk AFM coupling below the Neel temperature (4–8 K). At temperatures higher than the bulk AFM/PM transition, a surface magnetic layer is proposed to develop, where the coupling between the magnetic moments located at magnetic impurities (Gd) is mediated by the Topological Surface State (TSS) via surface Dirac-fermion-mediated magnetic coupling. This hypothesis is supported by a gap opening at the Dirac point (DP) indicated by the surface-sensitive ARPES, a weak hysteresis loop measured by SQUID at temperatures between 30 and 100 K, XMCD measurements demonstrating a surface magnetic moment at 70 K and a temperature dependence of the electrical resistance exhibiting a mid-gap semiconducting behavior up to temperatures of 100–130 K, which correlates with the temperature dependence of the surface magnetization and confirms the conclusion that only TSS are located at the EF. The increase of the TSS’s spectral weight during resonant ARPES at a photon energy corresponding to the Gd 4d-4f edge support the hypothesis of a magnetic coupling between the Gd ions via the TSS and corresponding magnetic moment transfer at elevated temperatures. Finally, the observed out-of-plane and in-plane magnetization induced by synchrotron radiation (SR) due to non-equal depopulation of the TSS with opposite momentum, as seen through change in the Dirac gap value and the k∥-shift of the Dirac cone (DC) states, can be an indicator of the modification of the surface magnetic coupling mediated by the TSS.

We have studied the magnetization process of the new insulating ferromagnetic semiconductor (Al,Fe)Sb by means of x-ray magnetic circular dichroism. For an optimally doped sample with 10% Fe, a magnetization was found to rapidly increase at low magnetic fields and to saturate at high magnetic fields at room temperature, well above the Curie temperature of 40 K. We attribute this behavior to the existence of nanoscale Fe-rich ferromagnetic domains acting as superparamagnets. By fitting the magnetization curves using the Langevin function representing superparamagnetism plus the paramagnetic linear function, we estimated the average magnetic moment of the nanoscale ferromagnetic domain to be $300{\ensuremath{\mu}}_{\mathrm{B}}\ensuremath{-}400{\ensuremath{\mu}}_{\mathrm{B}}$ and the fraction of Fe atoms participating in the nanoscale ferromagnetism to be $\ensuremath{\sim}50%$. Such behavior was also reported for (In,Fe)As:Be and Ge:Fe and seems to be a universal characteristic of the Fe-doped ferromagnetic semiconductors. Further Fe doping up to 14% led to the weakening of the ferromagnetism, probably because antiferromagnetic superexchange interaction between nearest-neighbor Fe-Fe pairs becomes dominant.

In order to understand the mechanism of the ferromagnetism in the ferromagnetic semiconductor Ga 1 − xMn xAs [(Ga,Mn)As], we have investigated the magnetic behavior on a microscopic level through systematic temperature ( T)- and magnetic field ( H)-dependent soft x-ray magnetic circular dichroism (XMCD) experiments at the Mn L 2 , 3 absorption edges. The T and H dependences of XMCD intensities have been analyzed using a model consisting of the ferromagnetic (FM), paramagnetic, and superparamagnetic (SPM) components. Intriguingly, we have found a common behavior for the ferromagnetic ordering process in (Ga,Mn)As samples with different Mn concentrations (4% and 10.8%) and different Curie temperature ( T C) values (65, 120, and 164 K). In particular, the SPM component develops well above T C, indicating that local FM regions are formed well above T C. The present findings indicate that the onset of ferromagnetic ordering is triggered by local electronic states around the substitutional Mn ions rather than uniform electronic states considered by mean-field theories. Insight into the most representative ferromagnetic semiconductor, (Ga,Mn)As, provided by the present study will be an important step in understanding the mechanism of ferromagnetic ordering in various ferromagnetic semiconductor families.

EuPd3 is a rare Eu-based compound, whose Eu ions are in a trivalent state. The electronic structure of EuPd3 was investigated by angle-resolved photoemission spectroscopy (ARPES) using soft x rays....

We have performed x-ray magnetic circular dichroism (XMCD) measurements on the iron-based superconductor Sr$_2$VFeAsO$_{3-\delta}$ to study the origin of weak ferromagnetism (WFM) reported for this compound. While Fe 3$d$ electrons show a magnetic response similar to the other iron pnictides, signals from V 3$d$ electrons remain finite at zero magnetic field and may be responsible for the WFM.

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism measurements were performed at the Ni and Fe ${L}_{2,3}$ absorption edges for $\mathrm{N}{\mathrm{i}}_{x}\mathrm{F}{\mathrm{e}}_{4\ensuremath{-}x}\mathrm{N}\phantom{\rule{4pt}{0ex}}(x=1$ and 3) epitaxial films. Spectral line-shape analysis and element-specific magnetic moment evaluations are presented. Shoulders at approximately 2 eV above the Ni ${L}_{2,3}$ main peaks in the XAS spectrum of $\mathrm{N}{\mathrm{i}}_{3}\mathrm{FeN}$ were interpreted to originate from hybridization of orbitals between Ni $3d$ at face-centered (II) sites and N $2p$ at body-centered sites, while such features were missing in $\mathrm{NiF}{\mathrm{e}}_{3}\mathrm{N}$ film. Similar shoulders were observed at Fe ${L}_{2,3}$ edges in both films. These results indicate that the orbitals of Ni atoms did not hybridize with those of N atoms in the $\mathrm{NiF}{\mathrm{e}}_{3}\mathrm{N}$ film. Hence, Ni atoms preferentially occupied corner (I) sites, where the hybridization was weak because of the relatively long distance between Ni at I sites and N atoms. The relatively large magnetic moment deduced from sum-rule analysis of $\mathrm{NiF}{\mathrm{e}}_{3}\mathrm{N}$ also showed a good agreement with the presence of Ni atoms at I sites.

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.

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.

$\mathrm{G}{\mathrm{e}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}$ (GeMn) granular thin films are a unique and promising material for spintronic applications owing to their large positive magnetoresistance (MR). Previous studies of GeMn have suggested that the large MR is related to the nanospinodal decomposition of GeMn into Mn-rich ferromagnetic nanoparticles and a Mn-poor paramagnetic matrix. However, the microscopic origin of the MR has not yet been clarified. Here, we develop a method to separately investigate the magnetic properties of the nanoparticles and the matrix, utilizing the extremely high sensitivity of x-ray magnetic circular dichroism (XMCD) to the local magnetic state of each atom. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that the spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo first order magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.

We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, Ge1−xFex (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3d electrons are strongly hybridized with the Ge 4p states, and have a large orbital magnetic moment relative to the spin magnetic moment; i.e., morb/mspin ≈ 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20–100 K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature.

We have performed x-ray photoemission spectroscopy (XPS), x-ray absorption spectroscopy (XAS), and resonant photoemission spectroscopy (RPES) measurements of Mn-implanted 3$C$-SiC (3$C$-SiC:Mn) and carbon-incorporated Mn$_{5}$Si$_{2}$ (Mn$_{5}$Si$_{2}$:C). The Mn 2$p$ core-level XPS and XAS spectra of 3$C$-SiC:Mn and Mn$_{5}$Si$_{2}$:C were similar to each other and showed "intermediate" behaviors between the localized and itinerant Mn 3$d$ states. The intensity at the Fermi level was found to be suppressed in 3$C$-SiC:Mn compared with Mn$_{5}$Si$_{2}$:C. These observations are consistent with the formation of Mn$_{5}$Si$_{2}$:C clusters in the 3$C$-SiC host, as observed in a recent transmission electron microscopy study., Comment: 4 pages, 3 figures

The electronic structure of the Cr ions in Zn1−x Cr x Te (x=0.03 and 0.15) has been investigated using X-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy. Magnetic-field (H) and temperature (T) dependences of the Cr L 2,3 XMCD spectra well corresponded to the behavior of the magnetization measured by a SQUID magnetometer. The line shape of the Cr L 2,3 XMCD spectra was independent of H,T, and x, indicating that the ferromagnetism was originated from the same Cr electronic states independent of Cr concentration. The Cr 3d partial density of states (DOS) showed a peak at the top of the valence band but there was no DOS at the Fermi level, corresponding to their insulating behaviors.

Magnetically doped topological insulators, possessing an energy gap created at the Dirac point through time-reversal-symmetry breaking, are predicted to exhibit exotic phenomena including the quantized anomalous Hall effect and a dissipationless transport, which facilitate the development of low-power-consumption devices using electron spins. Although several candidates of magnetically doped topological insulators were demonstrated to show long-range magnetic order, the realization of the quantized anomalous Hall effect is so far restricted to the Cr-doped (Sb,Bi)2Te3 system at extremely low temperature; however, the microscopic origin of its ferromagnetism is poorly understood. Here we present an element-resolved study for Cr-doped (Sb,Bi)2Te3 using X-ray magnetic circular dichroism to unambiguously show that the long-range magnetic order is mediated by the p-hole carriers of the host lattice, and the interaction between the Sb(Te) p and Cr d states is crucial. Our results are important for material engineering in realizing the quantized anomalous Hall effect at higher temperatures., Magnetically doped topological insulators may exhibit exotic transport phenomena such as the quantum anomalous Hall effect, however the underlying mechanisms of ferromagnetic order are currently debated. Here, the authors reveal stabilized ferromagnetism in Cr-doped (Sb,Bi)2Te3 mediated by Te and Sb p-hole carriers.

The temperature evolution of the electronic structure of a Ni-Fe(Co)-Ga/MgO(100), Heusler-type, ferromagnetic shape-memory alloy thin film has been followed by a bulk-sensitive hard x-ray photoelectron spectroscopy, element-selective soft x-ray magnetic circular dichroism, and first-principles calculation. The reversible changes of the electronic states near the Fermi energy show a hysteresis associated with the martensitic phase transition (MPT), where the pseudogap opens on cooling and closes again on warming. In addition, the Ni $3d$ spin magnetic moment increases by approximately two times across the MPT, whereas the change of Fe $3d$ moment is moderate. By comparing the experimental results with the calculated spin-resolved density of states, we conclude that the band Jahn-Teller effect of Ni $3d$ and Fe $3d$ orbitals is responsible for MPT.

Thin films of the ferromagnetic metal SrRuO3 (SRO) show a varying easy magnetization axis depending on the epitaxial strain and undergo a metal-to-insulator transition with decreasing film thickness. We have investigated the magnetic properties of SRO thin films with varying thicknesses fabricated on SrTiO3(001) substrates by soft x-ray magnetic circular dichroism (XMCD) at the Ru M2,3 edge. Results have shown that, with decreasing film thickness, the film changes from ferromagnetic to non-magnetic around 3monolayer thickness, consistent with previous magnetization and magneto-optical Kerr effect measurements. The orbital magnetic moment perpendicular to the film was found to be ~ 0.1{\mu}B/Ru atom, and remained nearly unchanged with decreasing film thickness while the spin magnetic moment decreases. Mechanism for the formation of the orbital magnetic moment is discussed based on the electronic structure of the compressively strained SRO film., Comment: 6 pages, 6 figures, Submitted in Phys. Rev. B

We report on a microscopic study of the evolution of ferromagnetism in the Ru substituted ferromagnetic superconductor FM SC UCoGe crystallizing in the orthorhombic TiNiSi type structure. For that purpose, two single crystals with composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge have been prepared and characterized by magnetization, AC susceptibility, specific heat and electrical resistivity measurements. Both compounds have been found to order ferromagnetically below TC 6.5 and 7.5 K, respectively, which is considerably higher than the TC 3 K of the parent compound UCoGe. The higher values of TC are accompanied by enhanced values of the spontaneous moment amp; 956;spont 0.11 amp; 956;B f.u. and amp; 956;spont 0.21 amp; 956;B f.u., respectively in comparison to the tiny spontaneous moment of UCoGe about 0.07 amp; 956;B f.u. . No sign of superconductivity was detected in either compound. The magnetic moments of the samples were investigated on the microscopic scale using polarized neutron diffraction PND and for UCo0.88Ru0.12Ge also by soft X ray magnetic circular dichroism XMCD . The analysis of the PND results indicates that the observed enhancement of ferromagnetism is mainly due to the growth of the orbital part of the uranium 5f moment amp; 956;UL, reflecting a gradual localization of the 5f electrons with Ru substitution. In addition, the parallel orientation of the U and Co moments has been established in both substituted compounds. The results are discussed and compared with related isostructural ferromagnetic UTX compounds T transition metals, X Si, Ge in the context of a varying degree of the 5f ligand hybridization

We have studied the chemical potential shift in La(1-x)Sr(x)MnO(3) as a function of doped hole concentration by core-level x-ray photoemission. The shift is monotonous, which means that there is no electronic phase separation on a macroscopic scale, whereas it is consistent with the nano-meter scale cluster formation induced by chemical disorder. Comparison of the observed shift with the shift deduced from the electronic specific heat indicates that hole doping in La(1-x)Sr(x)MnO(3) is well described by the rigid-band picture. In particular no mass enhancement toward the metal-insulator boundary was implied by the chemical potential shift, consistent with the electronic specific heat data., 7 pages, 3 figures, to be published in Europhysics Letters

We have investigated the spin and orbital magnetic moments of Fe in FePt nanoparticles in the $L$1${}_{0}$-ordered phase coated with $\mathrm{Si}{\mathrm{O}}_{2}$ by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Fe ${L}_{2,3}$ absorption edges. Using XMCD sum rules, we evaluated the ratio of the orbital magnetic moment (${M}_{\mathrm{orb}}$) to the effective spin magnetic moment (${M}_{\mathrm{spin}}^{\mathrm{eff}}$) of Fe to be ${M}_{\mathrm{orb}}/{M}_{\mathrm{spin}}^{\mathrm{eff}}=0.08$. This ${M}_{\mathrm{orb}}/{M}_{\mathrm{spin}}^{\mathrm{eff}}$ value is comparable to the value (0.09) obtained for FePt nanoparticles prepared by gas phase condensation, and is larger than the values ($\ensuremath{\sim}$0.05) obtained for FePt thin films, indicating a high degree of $L$1${}_{0}$ order. The hysteretic behavior of the FePt component of the magnetization was measured by XMCD. The magnetic coercivity (${H}_{c}$) was found to be as large as 1.8 T at room temperature, $\ensuremath{\sim}$3 times larger than the thin film value and $\ensuremath{\sim}$50 times larger than that of the gas phase condensed nanoparticles. The hysteresis curve is well explained by the Stoner-Wohlfarth model for noninteracting single-domain nanoparticles with the ${H}_{c}$ distributed from 1 to 5 T.

Metallic transition-metal oxides undergo a metal-to-insulator transition (MIT) as the film thickness decreases across a critical thickness of several monolayers (MLs), but its driving mechanism remains controversial. We have studied the thickness-dependent MIT of the ferromagnetic metal ${\mathrm{La}}_{0.6}$${\mathrm{Sr}}_{0.4}$${\mathrm{MnO}}_{3}$ by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. As the film thickness was decreased across the critical thickness of the MIT (6--8 ML), a gradual decrease of the ferromagnetic signals and a concomitant increase of paramagnetic signals were observed, while the Mn valence abruptly decreased towards ${\mathrm{Mn}}^{3+}$. These observations suggest that the ferromagnetic phase gradually and most likely inhomogeneously turns into the paramagnetic phase and both phases abruptly become insulating at the critical thickness.

We have studied the substitution and temperature dependences of the B s p -Yb d -derived conduction-band states in Yb 1- x Lu x B 12 ( x = 0.25, 0.50, 0.75, and 1.00) by high-resolution photoemissi...

Angle-resolved photoelectron spectroscopy (ARPES) measurements were made in the Ce 3d → 4f resonance energy region for the paramagnetic state of CeRu 2 Si 2 , CeRu 2 (Si 0.82 Ge 0.18 ) 2 , and LaRu 2 Si 2 to investigate a variation of band structures around the quantum critical point (QCP). The observed band structures are very similar between CeRu 2 Si 2 and CeRu 2 (Si 0.82 Ge 0.18 ) 2 . The results indicate that the Ce 4f electrons in the paramagnetic state have an itinerant character and participate in the formation of energy bands both in CeRu 2 Si 2 and CeRu 2 (Si 0.82 Ge 0.18 ) 2 , and the change of the band structures in the paramagnetic states should be continuous around the QCP of the CeRu 2 (Si 1-x Ge x ) 2 system.

We have performed a detailed temperature-dependent photoemission study of the conduction-band states in the Kondo insulator YbB12 using single crystalline samples. Measurements with improved energy resolution have revealed (pseudo)gaps of two energy scales. The size of the narrower gap ,10 meV and its disappearance at high temperatures are consistent with the temperature dependence of the electrical resistivity and the magnetic susceptibility. The larger pseudogap of ,100 meV depends on temperature even at room temperature. We discuss how the characteristics of the Kondo insulator are reflected in the conduction-band photoemission spectra. [S0031-9007(98)08323-9]

We have studied the electronic and magnetic properties of epitaxially grown CaMn 1 - x Ru x O 3 ( x = 1.0 , 0.5) thin films by X-ray magnetic circular dichroism (XMCD) and hard X-ray photoemission spectroscopy (HXPES). The XMCD studies indicated that the spin moments of Mn and Ru are aligned in the opposite directions. The HXPES spectra indicated the Ru 4d states at around the Fermi edge ( E F ) and the Mn 3d states below E F . From these results, we propose that the localized Mn 3d t 2 g states and the itinerant Ru 4d t 2 g band are antiferromagnetically coupled and give rise to ferromagnetism, in analogy with the mechanism proposed for the double perovskite oxides such as Sr 2 FeMoO 6 .

We have performed angle-resolved photoemission spectroscopy experiments on paramagnetic UFeGa 5 using soft X-ray synchrotron radiation ( h ν=500 eV) and derived its bulk- and U 5 f -sensitive electronic structure. The topology of the experimental Fermi surface is well explained by the LDA calculation treating U 5 f electrons as being itinerant, suggesting that the U 5 f states of this compound can be essentially understood within the itinerant-electron model.

The metal–insulator (MI) transition in quasi-one-dimensional compound V6O13 has been investigated by angle-resolved photoemission spectroscopy (ARPES) at the photon energy of h ν = 10 eV using synchrotron radiation and optical study below 2 eV. Along the b ‖ direction, a clear Fermi cutoff and a band dispersion near E F are observed in the ARPES spectra. The energy distribution curves (EDC) show an opening of a gap ∼ 0.2 eV across the transition temperature T MI = 150 K. The ARPES at h ν = 10 eV is confirmed to be a bulk-sensitive spectroscopy with high resolutions in energy and momenta.

The electronic structure of doped Mn in (Ga,Mn)As is studied by resonant inelastic X-ray scattering (RIXS). From configuration-interaction cluster-model calculations, the line shapes of the Mn $L_3$ RIXS spectra can be explained by $d$-$d$ excitations from the Mn$^{3+}$ ground state, dominated by charge-transferred states, rather than a Mn$^{2+}$ ground state. Unlike archetypical $d$-$d$ excitation, the peak widths are broader than the experimental energy resolution. We attribute the broadening to a finite lifetime of the $d$-$d$ excitations, which decay rapidly to electron-hole pairs in the host valence and conduction bands through hybridization of the Mn $3d$ orbital with the ligand band., 5 pages, 3 figures

The coercivity of La$_{1-x}$Sr$_x$MnO$_3$ thin films can be enhanced by Ru substitution for Mn. In order to elucidate its mechanism, we performed soft x-ray absorption and magnetic circular dichroism measurements at the Ru M$_{2,3}$ and Mn L$_{2,3}$ edges. We found that the spin direction of Ru and Mn are opposite and that Ru has a finite orbital magnetic moment. Cluster-model analysis indicated that the finite orbital magnetic moment as well as the reduced spin moment of Ru result from local lattice distortion caused by epitaxial strain from the SrTiO$_3$ substrate in the presence of spin-orbit interaction., Comment: 10 pages, 4 figures, 2 tables, accepted Applied Physics Letters

BiFeO$_3$ (BFO) shows both ferroelectricity and magnetic ordering at room temperature but its ferromagnetic component, which is due to spin canting, is negligible. Substitution of transition-metal atoms such as Co for Fe is known to enhance the ferromagnetic component in BFO. In order to reveal the origin of such magnetization enhancement, we performed soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD) studies of BiFe$_{1-x}$Co$_x$O$_3$ ({\it x} = 0 to 0.30) (BFCO) thin films grown on LaAlO$_3$(001) substrates. The XAS results indicated that the Fe and Co ions are in the Fe$^{3+}$ and Co$^{3+}$ states. The XMCD results showed that the Fe ions show ferromagnetism while the Co ions are antiferromagnetic at room temperature. The XAS and XMCD measurements also revealed that part of the Fe$^{3+}$ ions are tetrahedrally co-ordinated by oxygen ions but that the XMCD signals of the octahedrally coordinated Fe$^{3+}$ ions increase with Co content. The results suggest that an impurity phase such as the ferrimagnetic $\gamma$-Fe$_2$O$_3$ which exists at low Co concentration decreases with increasing Co concentration and that the ferromagnetic component of the Fe$^{3+}$ ion in the octrahedral crystal fields increases with Co concentration, probably reflecting the increased canting of the Fe$^{3+}$ ions., Comment: Accepted in J. Applied Physics

Angle-resolved photoemission spectra of 1T-TaS2 have been measured to reveal the electronic structure of valence bands in the incommensurate (IC) and commensurate (C) charge density wave (CDW) phases. In the ICCDW phase at 370 K, Ta 5d states are observed as a single branch along the Γ–M direction over the binding energy range EB=0–1.2 eV. In the CCDW phase at 17 K, on the other hand, Ta 5d states are divided into three sub-band manifolds centered at EB=0.2, 0.5 and 1.0 eV. The former sub-band at EB=0.2 eV is less dispersive, while latter two show clear dispersive nature with the bandwidths of ∼0.5 and 0.3 eV. Furthermore, the spectral intensities are concentrated around the original Ta 5d band.

The temperature dependences of the Yb 4f and 3d states of Kondo semiconductor YbB 12 single crystal have been studied by high-resolution photoemission spectroscopy taken at hν =100 and 5951 eV. The Yb 2+ 4f 7/2 state at the Fermi level is enhanced on cooling. With improved energy resolution, we discover an additional quasi-particle peak at 15 meV that developes below 60 K. From the Yb 3d spectrum at 22 K, the Yb valence is estimated to be∼2.88.

High-resolution low-energy excited photoemission spectra of YbInCu4 with a first-order valence transition at TV∼42 K have been measured. In the spectra taken at hν =7 eV, the hybridization between the conduction-band and Yb 4f states is observed as a structure at ∼47 meV below the Fermi level and drastically increases at TV with decreasing temperature.