Seungho Seong

Soft X-ray absorption spectroscopy study of multiferroic Bi-substituted Ba1−xBixTi0.9Fe0.1O3

The electronic structures of multiferroic oxides of Ba1−xBixTi0.9Fe0.1O3 (0 ≤ x ≤ 0.12) have been investigated by employing photoemission spectroscopy and soft X-ray absorption spectroscopy (XAS). The measured Fe and Ti 2p XAS spectra show that Ti ions are in the Ti4+ states for all x and that Fe ions are Fe2+-Fe3+ mixed-valent for x > 0. The valence states of Fe ions are found to be nearly trivalent for x=0 and decrease with increasing x from being nearly trivalent (v(Fe) ~ 3) for x = 0 to v(Fe) ~ 2.6 for x = 0.12. The valence states of both Ti and Ba ions do not change for all x ≤ 0.12. Based on the obtained valence states of Fe ions, the electronic and the magnetic properties of Ba1−xBixTi0.9Fe0.1O3 are explored.

Soft X-ray Synchrotron-Radiation Spectroscopy Study of [Co/Pd] Multilayers as a Function of the Pd Sublayer Thickness

We have investigated the electronic structures of intermetallic multilayer (ML) films of [Co(2A)/Pd(xA)] (x: the thickness of the Pd sublayer; x = 1 A, 3 A, 5 A, 7 A, 9 A) by employing soft X-ray absorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD). Both Co 2p XAS and XMCD spectra are found to be similar to one another, as well as to those of Co metal, providing evidence for the metallic bonding of Co ions in [Co/Pd] ML films. By analyzing the measured Co 2p XMCD spectra, we have determined the orbital magnetic moments and the spin magnetic moments of Co ions in [Co(2A)/Pd(xA)] ML films. Based on this analysis, we have found that the orbital magnetic moments are enhanced greatly when x increases from 1 A to 3 A, and then do not change much for x ≥ 3 A. This finding suggests that the interface spin-orbit coupling plays an important role in determining the perpendicular magnetic anisotropy in [Co/Pd] ML films.

Soft X-ray Synchrotron-Radiation Spectroscopy Study of Half-metallic Mn3Ga Heusler Alloy

By employing photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS), the electronic structure of the candidate half-metallic antiferromagnet of Mn3Ga Heusler compound has been investigated. We have studied two ball-milled Mn3Ga powder samples, one after annealing and the other without annealing, respectively. Based on the Mn 2p XAS study, we have found that Mn ions are nearly divalent in Mn3Ga and that the Mn ions having the locally octahedral symmetry and those having the locally tetrahedral symmetry are both present in Mn3Ga. We have found relatively good agreement between the measured valence-band PES spectrum of Mn3Ga and the calculated density of states, which is in agreement with the half-metallic electronic structure of Mn3Ga.

Photoelectron Spectroscopy Study of the Semiconductor Electrode Nanomaterials for the Dye Synthesized Solar Cell

The electronic structures of the potential candidate semiconductor nanoparticles for dye-sensitized solar cell (DSSC), such as and , have been investigated by employing X-ray photoemission spectroscopy (XPS). The measured X-ray diffraction patterns show that and samples have the single-phase ilmenite-type structure and the inverse spinel structure, respectively. The measured Zn 2p and Sn 3d core-level XPS spectra reveal that the valence states of Zn and Sn ions are divalent (Zn 2+) and tetravalent (Sn 4+), respectively, in both and . On the other hand, the shallow core-level measurements show that the binding energies of Sn 4d and Zn 3d core levels in are lower than those in . This work provides the information on the valence states of Zn and Sn ions and their chemical bonding in and .