Jihoon Hwang

Valence states and electronic structures of Co and Mn substituted spin gapless semiconductor PbPdO2

Electronic structures of Pb(Pd0.9T0.1)O2 (T = Mn, Co) spin gapless semiconductors have been investigated by employing soft X-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES). The valence states of Co and Mn ions are found to be mixed-valent (∼2.7) and tetravalent, respectively. The measured valence-band PES and O 1s XAS spectra show that both PbPdO2 and PbPd0.9Co0.1O2 are small-gap semiconductors. This finding is supported by the calculated band structures, obtained in the density functional theory with the modified Becke-Johnson potential (mBJ) scheme. This work also shows evidence for the existence of the phase separation in Mn-substituted PbPd0.9Mn0.1O2.

Size-dependent structural evolution of the biomineralized iron-core nanoparticles in ferritins

The structural identity of the biomineralized iron core nanoparticles in Helicobacter pylori ferritins (Hpfs) has been determined by employing soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism. Valence states of Fe ions are nearly trivalent in all Hpfs, indicating that the amount of magnetite (Fe3O4) is negligible. With increasing filling of Fe ions, the local configurations of Fe3+ ions change from the mixture of the tetrahedral and octahedral symmetries to the octahedral symmetry. These results demonstrate that the biomineralization of the ferritin core changes from maghemite-like (γ-Fe2O3) formation to hematite-like (α-Fe2O3) formation with increasing Fe content.

Phase separation in thermoelectric delafossite CuFe1−xNixO2 observed by soft x-ray magnetic circular dichroism

Electronic structures of Ni-doped CuFe1−xNixO2 delafossite oxides (0 ≤ x ≤ 0.03) have been investigated by employing soft x-ray magnetic circular dichroism (XMCD). Finite XMCD signals are observed for Fe, Ni, and Cu 2p states, and valence states of Cu, Fe, and Ni ions are nearly monovalent (Cu+), trivalent (Fe3+), and divalent (Ni2+), respectively, for all x ≤ 0.03. Tiny magnetic impurities could be detected by employing XMCD. Fe and Ni 2p XMCD signals are identified due to ferrimagnetic spinel impurities of CuFe2O4 and NiFe2O4. XMCD signals for Cu 2p states arise from divalent Cu2+ ions. Thermoelectrical properties are found to be very sensitive to the very little impurity phase present in delafossite oxides.

Soft x-ray magnetic circular dichroism study of valence and spin states in FeT2O4 (T = V, Cr) spinel oxides

Electronic structures of spinel oxides FeT2O4 (T = V, Cr) have been investigated by employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS). XAS reveals that Cr and V ions are trivalent, and that Fe ions are nearly divalent in FeT2O4 (T = V, Cr). Finite XMCD signals are observed in FeV2O4 at T = 80 K, while they are very weak in FeCr2O4. XMCD shows that Fe spins are antiparallel to V and Cr spins, with the V and Cr spins being canted from Fe spins, which suggests a Yafet-Kittel type triangular spin configuration in FeT2O4 (T = V, Cr).

Soft x-ray synchrotron radiation spectroscopy study of CuFe1-xNixO2 (0≤ x ≤0.03) delafossite oxides

Electronic structures of Ni-doped CuFe1-x Nix O2 delafossite oxides (x = 0, 0.015, and 0.03) have been investigated by employing soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism (XMCD). It is found that the valence states of Cu, Fe, and Ni ions are nearly monovalent (Cu+), trivalent (Fe3+), and divalent (Ni2+), respectively, and that they do not change with x. In contrast, the Cu 2p XMCD signals, which arise from the Cu2+ states, increase with increasing x. This study suggests that the increasing XMCD signals are presumably related to the formation of ferrimagnetic spinel impurities in CuFe1-x Nix O2.

Differences in the Electronic Structures of Bulk and Powder FeV 2 O 4 Spinel Oxide Investigated by Using Synchrotron Radiation

The electronic structure of ferrimagnetic spinel oxide of has been investigated by employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). The Fe 2p and V 2p XAS spectra show that the valence states of Fe and V ions are mixed-valent states and states, respectively. In Fe 2p XMCD spectra, finite XMCD signals are observed for divalent states only, but not for states. This finding indicates that the magnetic moments of ions are ordered ferromagnetically but that those of ions are cancelled, implying that ions play an important role in determining magnetic properties of .

Soft x-ray Synchrotron Radiation Spectroscopy Study of Molecule-based Nano Bioparticles Containing Fe

By employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD), the electronic structures of molecule-based nano bioparticles, such as Helicobacter pylori ferritin (H. pylori ferritin), Heme, -type Prussian Blue (M

Electronic structures of SrMn1–xMoxO3 (0≤x≤0.75) perovskite oxides investigated by XAS and PES

Electronic structures of perovskite oxides of SrMn1-x Mox O3 (0 ≤x≤ 0.75) have been investigated by employing soft x-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES). It is found that the valence states of Mn ions change systematically from Mn4+ for x = 0, to nearly Mn3+ for x = 0.3, and Mn2+ for x = 0.5, and then remain as Mn2+ for x≥0.5. Both the Mo 3d core-level PES and Mo 3p XAS spectra show that the valence states of Mo ions remain unchanged as being hexavalent (Mo6+) for x≤0.5 but that they decrease for x>0.5 with increasing x. This study shows that Mo ions are mixed-valent for x>0.5 in SrMn1-x Mox O3, either with the Mo4+–Mo6+ configuration or with the Mo4+–Mo5+–Mo6+ configuration.