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Register a new userElectronic Structure and Magnetic Properties of Half-metallic Ferrimagnet Mn$_{2}$VAl Probed by Soft X-ray Spectroscopies
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We have studied the electronic structure of ferrimagnetic Mn2VAl single crystal 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 constitute elements, supporting the spin polarized states at the Fermi level. The Mn $L_{2,3}$ XAS and XMCD spectra are reproduced by the spectral simulation based on density-functional theory (DFT), indicating itinerant character of the Mn 3d states. On the other hand, V $3d$ electrons are rather localized since the ionic model can qualitatively explain the V $L_{2,3}$ XAS and XMCD spectra as well as the local dd excitation revealed by V $L_3$ RIXS.
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The density of non-quasiparticle states in the ferrimagnetic full-Heuslers Mn$_2$VAl alloy is calculated from first principles upon appropriate inclusion of correlations. In contrast to most half-metallic compounds, this material displays an energy gap in the majority-spin spectrum. For this situation, non-quasiparticle states are located below the Fermi level, and should be detectable by spin-polarized photoemission. This opens a new way to study many-body effects in spintronic-related materials.
The electronic properties of the Mn:GaSe interface, produced by evaporating Mn at room temperature on an epsilon-GaSe(0001) single crystal surface, have been studied by soft X-ray spectroscopies. Substitutional effects of Mn replacing Ga cations and Mn-Se hybridization effects are found both in core level and valence band photoemission spectra. The Mn cation valence state is probed by XAS measurements at the Mn L-edge, which indicate that Mn diffuses into the lattice as a Mn2+ cation with negligible crystal field effects. The Mn spectral weight in the valence band is probed by resonant photoemission spectroscopy at the Mn L-edge, which also allowed an estimation of the charge transfer and Mott-Hubbard energies on the basis of impurity-cluster configuration-interaction model of the photoemission process. The charge transfer energy is found to scale with the energy gap of the system. Competing effects of Mn segregation on the surface have been identified, and the transition from the Mn diffusion through the surface to the segregation of metallic layers on the surface has been tracked by core-level photoemission.
We have studied the electronic and magnetic states of Co and Mn atoms at the interface of the Co$_mathrm{2}$Mn$_{beta}$Si (CMS)/MgO ($beta$=0.69, 0.99, 1.15 and 1.29) magnetic tunnel junction (MTJ) by means of x-ray magnetic circular dichroism. In particular, the Mn composition ($beta$) dependences of the Mn and Co magnetic moments were investigated. The experimental spin magnetic moments of Mn, $m_mathrm{spin}$(Mn), derived from XMCD weakly decreased with increasing Mn composition $beta$ in going from Mn-deficient to Mn-rich CMS films. This behavior was explained by first-principles calculations based on the antisite-based site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defect, not vacancies, to accommodate off-stoichiometry. Furthermore, the experimental spin magnetic moments of Co, $m_mathrm{spin}$(Co), also weakly decreased with increasing Mn composition. This behavior was consistently explained by the antisite-based SSFU model, in particular, by the decrease in the concentration of Co$_mathrm{Mn}$ antisites detrimental to the half-metallicity of CMS with increasing $beta$. This finding is consistent with the higher TMR ratios which have been observed for CMS/MgO/CMS MTJs with Mn-rich CMS electrodes.
We present the self-interaction corrected local spin density (SIC-LSD) electronic structure and total energy calculations, leading also to valencies of the ground state configurations, for the half-metallic double perovskites such as Sr$_{2}$FeMoO$_{6}$, Ba$_{2}$FeMoO$_{6}$, Ca$_{2}$FeMoO$_{6}$, and Ca$_{2}$FeReO$_{6}$. We conclude that the Fe and Mo (or Re) spin magnetic moments are anti-parallel aligned, and the magnitude of the hybridization induced moment on Mo does not vary much between the different compounds. The hybridization spin magnetic moment on Re is of the order of -1.1 $mu_{B}$, while that on Mo is about -0.4 $mu_{B}$, independently of the alkaline earth element. Also the electronic structure of all the compounds studied is very similar, with a well defined gap in the majority spin component and metallic density of states for the minority spin component, with highly hybridized Fe, Mo (or Re), and oxygen bands.
We report a combined study for the electronic structures of ferromagnetic CeAgSb$_2$ using soft X-ray absorption (XAS), magnetic circular dichroism (XMCD), and angle-resolved photoemission (ARPES) spectroscopies. The Ce $M_{4, 5}$ XAS spectra show very small satellite structures, reflecting a strongly localized character of the Ce $4f$ electrons. The linear dichroism effects in the Ce $M_{4, 5}$ XAS spectra demonstrate the ground state Ce $4f$ symmetry of $Gamma{_6}$, the spatial distribution of which is directed along the $c$-axis. The XMCD results give support to the picture of local-moment magnetism in CeAgSb$_2$. Moreover it is also found that the theoretical band dispersions for LaAgSb$_2$ provides better description of the ARPES band structures than those for CeAgSb$_2$. Nevertheless, ARPES spectra at the Ce $3d$-$4f$ resonance show the momentum dependence for the intensity ratio between Ce $4f^{1}_{5/2}$ and $4f^{1}_{7/2}$ peaks in a part of the Brillouin zone, suggesting the non-negligible momentum dependent hybridization effect between the Ce $4f$ and the conduction electrons. This is associated with the moderate mass enhancement in CeAgSb$_2$.
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