G. Kim

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 values of the cations in selenospinel Cu(Cr,Ti)2Se4

A long-standing issue about the Cu valency in selenospinel CuCr2Se4 was investigated by soft X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). Using the sensitivity of XAS and XMCD to the valence value of transition metal ion and its local symmetry, we checked the valence value of each cation in selenospinel CuCrxTi 2−xSe4 (x = 1.0, 1.1, 1.5, and 2.0) and obtained spectroscopic evidence that a small amount of the Cu cation changes the valency from Cu(I) to Cu(II) as the Cr concentration increases from 1.0 to 2.0. Dependence of the Cu(II) concentration and the mean field magnetic exchange energy on the Cr concentration suggests the Cu d-hole could play a crucial role in the intriguing magnetic/electrical properties of CuCr2Se4.

Scanning photoelectron microscopy study of Ge1−xTx (T=Cr, Fe) diluted ferromagnetic semiconductor single crystals

The chemical distributions and electronic structures of Ge1−xTx (T=Cr, Fe) diluted ferromagnetic semiconductors have been investigated by employing scanning photoelectron microscopy (SPEM), x-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). The SPEM images and PES spectra of Ge1−xTx show the stripe-shaped regions due to the inhomogeneous concentration distributions of T ions. T2p XAS spectra indicate that T ions are mainly in the divalent states, and that they do not form pure metal clusters. This study reveals that Ge1−xTx crystals are chemically phase-separated, suggesting that the observed ferromagnetic ordering in Ge1−xTx arises from the magnetic properties of the T-rich Ge1−xTx phases.

Photoemission spectroscopy and x-ray absorption spectroscopy study of delafossite AgTO2 (T=Fe,Co,Ni)

Electronic structures of delafossite AgTO2 (T=Fe,Co,Ni) have been investigated by using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The T 2p XAS spectra of AgTO2 show that Fe and Co ions are in the trivalent states but that Ni ions are mainly in the divalent states, suggesting that the metallic nature of AgNiO2 arises from hole carriers due to divalent Ni ions. The valence-band PES study of AgTO2 (T=Co,Ni) reveals that T 3d states are located close to EF and that the Ni 3d band is more metalliclike than the Co 3d band.

A case with improvement of blepharospasm by zolpidem.

Zolpidem is usually used for the treatment of insomnia as a hypnotic drug. It was also suggested to be effective in the treatment of dystonia in some studies. A 74-year-old woman had been suffering from frequent and intense bilateral spasms of the eyelids for 20 years. She has been treated with botulinum toxin injection and taken some medications. But, she experienced a little effect and was not satisfied with those treatments. Her symptom was improved after taking Zolpidem which had been prescribed for insomnia by her primary physician. She did not show any improvement after placebo injection and neostigmine test. This is the first report which shows improvement of isolated blepharospasm by Zolpidem in Korea. Zolpidem can be one of useful alternative pharmacological treatments for blepharospasm. Further randomized, blinded, placebo-controlled studies are needed to validate this finding.

Subcortical vascular dementia (SVaD) without hypertension (HTN) may be a unique subtype of vascular dementia (VaD)

Although HTN is the most important factor in the pathogenesis of SVaD, about 20% of patients with SVaD do not have HTN. We hypothesize that SVaD without HTN may have strong risk factors other than HTN, and the study on this group can elucidate the risk factors for SVaD. We included 332 patients with SVaD from the database of the Clinical Research Center for Dementia of South Korea (CREDOS) study. Among them, 26.2% of patients (87 out of 332) had no history of HTN. We analyzed the differences in risk factors, clinical features, and survival time of SVaD according to HTN. Contrary to our expectations, SVaD without HTN had less known vascular risk factors such as diabetes mellitus (DM), dyslipidemia, and obesity. In addition, SVaD without HTN had different clinical features including less depression, focal neurological signs or symptoms and more features of disinhibition. However, although SVaD without HTN had less known vascular risk factors that can shorten survival times, the survival times did not differ according to the presence of HTN. SVaD without HTN may be a unique subtype of SVaD and can be a target group for studies of unknown risk factors for SVaD.

Synchrotron radiation spectroscopy study of FeCr2X4 (X=S and Se)

Electronic structures of FeCr2X4 (X=S and Se) have been investigated by employing soft-x-ray absorption spectroscopy and soft-x-ray magnetic circular dichroism (XMCD). It is found that FeCr2S4 and FeCr2Se4 have similar electronic structures. The valence states of Cr and Fe ions are nearly trivalent (Cr3+) and divalent (Fe2+), respectively. The Fe 3d states are strongly hybridized to the X p states. The Fe and Cr 2p XMCD study provides evidence for the antiparallel alignment between Cr and Fe spins and the strong hybridization between the Fe 3d and X p electrons.

Valence states of transition-metal ions in cubic perovskites SrMn1−xFexO3

The electronic structures of SrMn1−xFexO3 (0⩽x⩽1) have been investigated by using photoemission spectroscopy (PES) and soft x-ray absorption spectroscopy (XAS). Mn ions in SrMnO3 are found to be in the nearly tetravalent (Mn4+) states, but with a small mixture of the Mn2+ configuration. With increasing x in SrMn1−xFexO3, Mn ions remain in the 4+ states. Fe ions in SrMn1−xFexO3 are also in the nearly tetravalent (Fe4+) states for the whole range of x. Valence-band PES reveals that the occupied Mn t2g3 states are located about 2.5eV below EF, while the occupied Fe t2g3eg1 states are broader than the Mn 3d occupied states, and are located between 3 and 6eV below EF. The large overlap between Fe 3d and the O 2p states is found in SrFeO3, reflecting the strong hybridization between the Fe 3d states and the O 2p states, in agreement with the metallic nature of SrFeO3.

Investigation of valence states and electronic structure of ferromagnetic double-perovskite La2MnNiO6 by using synchrotron radiation

The electronic structure of ferromagnetic double-perovskite La2MnNiO6 has been investigated by employing Mn and Ni 2p→3d resonant photoemission spectroscopy (RPES) and soft x-ray absorption spectroscopy (XAS). The Mn and Ni 2p XAS measurements show that Mn ions are formally tetravalent (3d3) and that Ni ions are formally divalent (3d8). Mn and Ni 2p→3d RPES shows that the occupied Mn 3d3 (t2g3↑) states are sharp and located around 2 eV below EF, while the occupied Ni 3d8 (t2g3↑t2g3↓eg2↑) states are broader than the Mn 3d states and they extend from EF to ∼5u2002eV below EF.

Electronic structures of AgNi1-xCoxO2AgNi1-xCoxO2 delafossite oxides

Electronic structures of AgNi1-xCoxO2AgNi1-xCoxO2(0⩽x⩽1)(0⩽x⩽1) delafossite oxides have been investigated by using photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS). T 2p XAS (T=CoT=Co, Ni) spectra of AgNi1-xCoxO2AgNi1-xCoxO2 show that the valence states of Co ions are trivalent and do not change with xx. In contrast, Ni ions are in the Ni2+–Ni3+Ni2+–Ni3+ mixed-valent states and the trivalent component increases with increasing xx. This finding suggests that the metallic nature of AgNi1-xCoxO2AgNi1-xCoxO2 for low values of xx arises from the divalent Ni ions. The valence-band PES study of AgNi1-xCoxO2AgNi1-xCoxO2 reveals that the Ni 3d states are more metallic like than the Co 3d states.