Masako Sakamaki

K 2 Cr 8 O 16 predicted as a half-metallic ferromagnet: Scenario for a metal-insulator transition

Based on the first-principles electronic structure calculations, we predict that a chromium oxide

NiO-like single layer formed on a Ni/Cu(001) thin film revealed by the depth-resolved x-ray absorption spectroscopy

{\text{K}}_{2}{\text{Cr}}_{8}{\text{O}}_{16}

Operation of a fast polarization-switching source at the Photon Factory

of hollandite type should be a half-metallic ferromagnet where the Fermi level crosses only the majority-spin band, whereas the minority-spin band has a semiconducting gap. We show that the double-exchange mechanism is responsible for the observed saturated ferromagnetism. We discuss possible scenarios of the metal-insulator transition observed at low temperature and we argue that the formation of the incommensurate long-wavelength density wave of spinless fermions caused by the Fermi-surface nesting may be the origin of the opening of the charge gap.

Real-time observation of CO oxidation reaction on Ir(111) surface at 33 ms resolution by means of wavelength-dispersive near-edge x-ray absorption fine structure spectroscopy

The formation of a 1-ML-thick NiO-like layer on a 5.5 ML Ni ultrathin film by Ni deposition on oxygen precovered Cu(001) is revealed by the depth-resolved x-ray absorption spectroscopy, and its magnetic properties are investigated. The surface layer exhibits a NiO-like x-ray absorption spectrum, while the underlying layers show a typical spectrum for a metallic Ni film. An uncompensated spin moment is observed in the NiO-like layer, which is antiparallel to the spin moment in the underlying Ni layers. These results demonstrate a potential to fabricate a sharp interface between ferromagnetic and antiferromagnetic materials.

Fast polarization switching in the soft X-ray region at PF BL-16A

We have been developing a fast polarization-switching source for the vacuum ultraviolet and soft X-ray region at the B15-16 straight section of the 2.5-GeV Photon Factory (PF) storage ring. The source consists of two tandem APPLE-II-type elliptically polarizing undulators (EPUs), namely, U#16-1 and U#16-2, and a fast kicker system. The target frequency of polarization switching is 10 Hz. As the first step, we installed U#16-1 and five identical bump kickers in the PF ring in March 2008. Then, we constructed U#16-2 and installed it in August 2010. The orbit switching operation at 10 Hz, for user experiments, started in January 2012. We describe the details of the operation status of two EPUs and the fast local bump system in this report.

X‐Ray Absorption Fine Structure Spectroscopy Study of Arsenate Adsorption on Schwertmannite

The CO oxidation reaction on Ir(111) is observed by the near-edge x-ray absorption fine structure (NEXAFS) spectroscopy in the soft x-ray region. A continuous data acquisition at 33 ms real-time resolution is realized for a single event of the reaction without the repetition, by adopting the wavelength-dispersive NEXAFS technique. The time evolution of the coverages for atomic O and molecular CO is quantitatively estimated during the reaction. The obtained activation energy is significantly larger than that on Pt(111).

Element Specific Magnetic Anisotropy Energy of Alternately Layered FeNi Thin Films

Recent development in fast polarization switching at the soft X-ray beamline, BL-16A in the Photon Factory is reported. Two APPLE-II type undulators installed in a tandem configuration enables us to achieve polarization switching between not only two opposite circular polarizations, but also the vertical and horizontal linear polarizations. An energy shift is observed during polarization switching due to a vertical modulation in the electron beam, which has been reduced by properly correcting the electron orbit.

Effect of surface roughness on magnetism of ultrathin Co films

We studied arsenate adsorption on schwertmannite by means of XAFS. Our results show that arsenate is bound to one or two iron octahedra and individual iron octahedra in schwertmannite become more regular after the adsorption. At the same time there is an increase of disorder in polymeric chains of iron octahedra. This suggests that the release of local strain is related to the overall stability of arsenate‐adsorbed schwertmannite.

Correlation of magnetism and structure for ultra thin Au/Co/Au films: Evidence for magnetoelastic effects

The element specific magnetic anisotropy energy (MAE) of alternately layered FeNi thin films grown on Ni (4–20 MLs)/Cu(001) is investigated by means of the X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE). Although surface Fe is known to show strong perpendicular magnetic anisotropy, the Ni-sandwiched Fe layer has a tiny MAE of 10±40 µeV. On the other hand, the Fe-sandwiched Ni layer has a positive MAE of 60±30 µeV. The total MAE simulated from the XMCD analysis shows good agreement with the MOKE result. We demonstrate that in-situ analysis of the element specific MAE gives a possible strategy for manipulating the magnetic anisotropy of multilayers.

Molecular orientation change during adsorption of NO and N2O on Ir(111) observed by real-time wavelength-dispersive x-ray absorption spectroscopy with polarization switching

Interface roughness effect on magnetic anisotropy of Co/Au are studied by using a Au substrate with sharp and rough surfaces by means of conventional and depth-resolved XMCD techniques. From the Co L-edge XMCD and sum rule analysis, the critical Co thickness of SRT from in-plane to perpendicular magnetization are found to be shifted from ~0.8 to ~1.1 nm by Au capping. We also found the sample with rough interface favors in-plane magnetization more than the sample with sharp interface. Compared to sharp sample, rough sample has smaller ml/ms values, and no significant probing-depth dependence is observed. These differences in the magnetic state at the interface between sharp and rough might be caused by structural changes. Moreover, ml/ms is lager for sharp sample especially at the interface. This can be interpreted as a large perpendicular anisotropy at the sharp interface, i.e. large Ks, while the magnetic anisotropy of the rough sample is determined by Kv more than by Ks.