Beom Hyun Kim

Magnetic couplings, optical spectra, and spin-orbit exciton in 5d electron Mott insulator Sr2IrO4.

Based on the microscopic model including spin-orbit coupling, on-site Coulomb and Hunds interactions, as well as crystal field effects, we investigate the magnetic and optical properties of Sr(2)IrO(4). Taking into account all intermediate state multiplets generated by virtual hoppings of electrons, we calculate the isotropic, pseudodipolar, and Dzyaloshinsky-Moriya coupling constants, which describe the experiment quite well. The optical conductivity σ(ω) evaluated by the exact diagonalization method shows two peaks at ~0.5 and ~1.0 eV in agreement with experiment. The two-peak structure of σ(ω) arises from the unusual Fano-type overlap between the electron-hole continuum of the J(eff)=1/2 band and the intrasite spin-orbit exciton observed recently in Sr(2)IrO(4).

Valence states and occupation sites in (Fe,Mn)3O4spinel oxides investigated by soft x-ray absorption spectroscopy and magnetic circular dichroism

The electronic structures of (Fe,Mn)3O4 spinel oxides have been investigated by employing soft-x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). We have determined the valence states as well as the occupation sites of Mn and Fe ions in Fe0.9Mn2.1O4 and MnFe2O4. Fe0.9Mn2.1O4 is found to be close to the inverse spinel (the inversion parameter y≈0.85), while MnFe2O4 is close to the normal spinel (y≈0.2). In Fe0.9Mn2.1O4, Fe ions are mainly trivalent and the majority of Fe3+ ions occupy the octahedral B sites, while Mn ions are mixed-valent with approximately 45% MnA2+ at the tetrahedral A sites and 55% MnB3+ ions at the octahedral B sites. In MnFe2O4, Mn ions are mainly divalent and the majority of Mn2+ ions occupy the tetrahedral A sites, while Fe ions are mainly trivalent and the majority of Fe3+ ions occupy the octahedral B sites.

Valence and spin states in delafossite AgNiO2 and the frustrated Jahn-Teller system ANiO2 "A=Li,Na…

Electronic structures of delafossite oxides AgNi1�xCoxO2 and the frustrated Jahn-Teller JT system ANiO2 A =L i,N a have been investigated by employing soft x-ray absorption spectroscopy and photoemission spectroscopy PES. It is found that Ni ions are in the Ni 2+ -Ni 3+ mixed-valent states and that the low-spin LS Ni 3+ component increases from LiNiO2 to AgNiO2 and NaNiO2, in agreement with the presence of the JT transition in NaNiO2 and the absence of the JT transition in LiNiO2 and AgNiO2 .I n AgNi 1�xCoxO2, the Ni 3+ component increases with x, while Co ions are in the LS Co 3+ states for all x, which is consistent with the metallic nature for low values of x. A good agreement is found between the measured PES spectra and the calculated local spin density approximation LSDA electronic structures of AgNiO2 and AgCoO2, but the pseudogap feature in PES of AgNiO2 is not described by the LSDA.

Effect of orbital symmetry on the anisotropic superexchange interaction

Employing the microscopic superexchange model incorporating the effect of spin–orbit interaction, we have investigated the Dzyaloshinsky–Moriya (DM) interaction in perovskite transition-metal (TM) oxides and explored the interplay between the DM interaction and the TM-3d orbital symmetry. For d3 and d5 systems with isotropic orbital symmetry, the DM vectors are well described by a simple symmetry analysis considering only the bond geometry. In contrast, the DM interaction for d4 systems with anisotropic orbital symmetry shows slightly different behavior, which does not obey simple symmetry analysis. The direction as well as the strength of the DM vector varies depending on the occupied orbital shape. We have understood this behavior based on the orbital symmetry induced by local crystal field variation.

Electronic structures and magnetic properties of a ferromagnetic insulator: La2MnNiO6

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Substrate-tuning of correlated spin-orbit oxides revealed by optical conductivity calculations.

exhibits concomitant antiferromagnetic (AFM) and structural transitions, both of which originate from the open-shell

Resonant inelastic x-ray scattering on single magnons at oxygen K edges

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Electronic Excitations in the Edge-shared Relativistic Mott Insulator: Na2IrO3

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Electronic Structure of the Kitaev Material α -RuCl 3 Probed by Photoemission and Inverse Photoemission Spectroscopies

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