Structural and oxygen content changes of hexagonal HoMnO manganite at the stability boundary in the perovskite phase have been studied by X-ray diffraction and thermogravimetry using in situ oxidation and reduction processes at elevated temperatures in oxygen and air. The oxygen storage properties during structural transformation between stoichiometric Hex0 and oxygen-loaded Hex1 phases, transition temperatures and kinetics of the oxygen incorporation and release are reported for materials prepared by the solid-state synthesis and high-impact mechanical milling. Long-term annealing experiments have shown that the Hex0 (δ = 0) → Hex1 (δ ≈ 0.28) phase transition is limited by the surface reaction and nucleation of the new phase for HoMnO 15MM. The temperatures of Hex0 ↔ Hex1 transitions have been established at 290 °C and 250 °C upon heating and cooling, respectively, at a rate of 0.1° min, also indicating that the temperature hysteresis of the transition could possibly be as small as 10 °C in the equilibrium. Ball-milling of HoMnO has only a small effect on improving the speed of the reduction/oxidation processes in oxygen, but importantly, allowed for considerable oxygen incorporation in air at a temperature range of 220-255 °C after prolonged heating. The Mn 2p XAS results of the Mn valence in oxygen loaded samples support the oxygen content determined by the TG method. The magnetic susceptibility data of the effective Mn valence gave inconclusive results due to dominating magnetism of the Ho ions. Comparison of HoMnO with previously studied DyMnO indicates that a tiny increase in the ionic size of lanthanide has a huge effect on the redox properties of hexagonal manganites and that practical properties could be significantly improved by synthesizing the larger average size (Y,Ln)MnO manganites.

By employing temperature (T)-dependent soft x-ray magnetic circular dichroism (XMCD) in the Fe and Cr 2p absorption edges, the electronic structures of Li0.5FeCr1.5O4 spinel ferrite, which exhibits magnetization compensation, have been investigated. This work provides evidence that (i) both Fe and Cr ions are trivalent, (ii) most of Fe3+ ions occupy the A (Td) sites, while Cr3+ ions occupy the B (Oh) sites, (iii) the magnetic moments of Fe and Cr ions are coupled antiferromagnetically, and (iv) they are reversed at ∼255 K. The sum-rule analysis of Fe and Cr 2p XMCD spectra reveals that the orbital magnetic moments of Fe and Cr ions in Li0.5FeCr1.5O4 are much larger than those of metallic Fe and Cr, implying the large spin–orbit coupling and the non-fully occupied t2g orbitals of Fe3+ and Cr3+ ions. Based on these findings, we have provided a comprehensive model for the electronic and spin configurations of Fe and Cr ions in (Fe)A[Li0.5Cr1.5]BO4.

The electronic structure of a Möbius Kondo insulator (MKI) candidate of CeRhSb has been investigated by employing angle-resolved photoemission spectroscopy (ARPES), and the density functional theory (DFT) and dynamical mean-field theory (DMFT) band calculations. The Fermi surfaces (FS's) and band structures are successfully measured for three orthogonal crystallographic directions. A sharp Ce 4f peak is observed at the Fermi level (EF), and its temperature (T)evolution agrees with that of the Ce 4f Kondo resonance. The metallic FS's are obtained for all three different (100), (010), and (001) planes. The Ce 4f FS's are described properly by the unfolded DFT calculations considering the reduced Ce-only unit cell. The T-dependence of Ce 4f states as well as the dispersive coherent Ce 4f bands are described well by the DMFT calculations, and reveal the anisotropic c-f hybridization. The photon energy dependence of the Fermi-edge states in CeRhSb reveals the 3D character, consistent with the bulk states dispersing to EF over a larger energy scale rather than the predicted Möbius topological surface states.

The electronic structures of SrRu1−xIrxO3 films (0≤x≤1) have been investigated by employing polarization-dependent soft X-ray absorption spectroscopy. In SrIrO3, the coherent quasi-particle peak at the Fermi level (EF) is clearly observed, reflecting the spin-orbit-coupled correlated metallic nature of SrIrO3. X-ray linear dichroism signals for x=0 and x=1 are negligibly weak, demonstrating the pseudo-cubic structure for SrRuO3 and the strong spin-orbit coupling in SrIrO3. In contrast, finite linear dichroism is observed for the intermediate x regime, indicating that the narrow dxz↓ and dyz↓ bands close to EF are occupied less than the wide dxy↓ band due to the enhanced in-plane hopping.