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The oxygen evolution reaction (OER) on the TiO2 surface at the solid–liquid interface was observed in real-time and operando using fluorescence-yield X-ray absorption spectroscopy (XAS) in the soft X-ray region. The OER was observed during a potential sweep with UV light on or off, focusing on the oxygen K-edge XAS. Although conventional XAS measurements require long measurement times, the spectra during the reaction were obtained every 3 s in the present experiment via wavelength-dispersive XAS technique. An increase in the X-ray absorption intensity at approximately 533.8 eV was observed during the potential sweep only with UV light on. The observed spectral change is discussed in relation to the reaction mechanism of the OER. The present technique can be applied to a wide range of analyses of (photo-) electrocatalysis and electrochemical reactions at solid–liquid interfaces to observe their products and intermediates during the reaction.

Real-time monitoring of oxygen species during the oxygen evolution reaction (OER) on cobalt oxide, one of the major OER electrocatalysts, was achieved through operando observation using wavelength-dispersive X-ray absorption spectroscopy (XAS) at the oxygen K-edge. The XAS spectra were collected every 3 s during electrode potential sweeping for the OER, and oxygen intermediate species related to the rate-determining step of the OER were detected just below the onset potential. Moreover, the cobalt L-edge XAS results demonstrate that the Co3O4 species dominates the surface of the electrode at a relatively high potential region, where the OER occurs. The present technique has significant potential for application in the analysis of solid–liquid interfaces, whose fundamental understanding is useful for further improvement of electrocatalysis.

The Hybrid Ring with a superconducting-linac injector as a highly flexible synchrotron radiation source to enable new experimental techniques and enhance many existing ones is proposed. It is designed to be operated with the coexistence of the storage (SR) bunches characterized by the performance of the storage ring, and the single-pass (SP) bunches characterized by the performance of the superconducting linac. Unique experiments can be performed by simultaneous use of the SR and SP beams, in addition to research with various experimental techniques utilizing the versatile SR beam and research in the field of ultrafast dynamics utilizing the ultrashort pulse of the SP beam. The extendability of the Hybrid Ring will allow it to be developed into a synchrotron radiation complex.

The antiperovskite ferrimagnet Mn4N has perpendicular magnetic anisotropy and small spontaneous magnetization, both of which are favorable properties for current induced domain wall motion. Previously we have investigated the magnetic structure of 3d-element-doped Mn4N thin films and demonstrated ultrafast domain wall velocities reaching 3000 m s−1 in the vicinity of the magnetic compensation composition of Ni-doped Mn4N at the current density of j = 1.2 × 1012 A m−2 at room temperature (RT). In this study, we investigate the effect of Au doping on the magnetic structure of Mn4N films, and present a composition ratio-dependent sign reversal of the anomalous Hall effect at RT. X-ray magnetic circular dichroism measurement revealed that the magnetic moment of the face-centered Mn atoms of Mn4−xAuxN reversed between x = 0.1 and 0.2, and became parallel to that of the corner-site Mn atoms for x = 0.2 and 0.3. This result suggests that the ferrimagnetic-ferromagnetic phase transition occurred in Au-doped Mn4N epitaxial films as in the In-doped Mn4N epitaxial films.

The X-ray magnetic circular dichroism detection of magnetic octupole moment has not been experimentally demonstrated so far. Here, the authors observe ferroic order of magnetic octupole in Mn3Sn, finding the exotic material functionalities related to the multipole order.

We measured X-ray absorption spectra of amorphous alumina with vacancy-type oxygen defects (AlOx) which exhibits the resistance random access memory (ReRAM) effect. We were able to detect changes in the electronic structure owing to the ReRAM effect. A major difference in the spectra near the O K-absorption edge was observed between a low resistance state (LRS) and a high resistance state (HRS). The subpeak profile within the band gap appeared in the LRS, while it was suppressed in the HRS. By contrast, the spectra near the Al K-absorption edge in the LRS and HRS appeared almost identical, indicating that no byproducts are generated. These findings imply that the distribution of charged electrons primarily changes near oxygen sites from the HRS to the LRS. The features of the subpeak profile are analogous to those of the mid-gap profile, as speculated by the first-principles calculation [Momida et al., Appl. Phys. Lett. 98, 042102 (2011)]. The LRS was mainly detected near the surface of the thin film.

Effect of energetic C60 cluster ion irradiation on magnetic properties in FeRh thin films was examined by SQUID and XMCD measurements. The XMCD signal for the C60 irradiated samples is larger than that for the C1 samples in the initial stage of the irradiation. In contrast, as for the irradiation with larger ion fluence, the XMCD spectrum for the sample irradiated with C1 ion is larger than that for the sample irradiated with C60 cluster ion. Although the magnetization for the C60 irradiation samples continuously decreases with increasing in the ion fluence, the saturation magnetization for the C1 irradiation samples increases with increasing in the ion fluence. Considering these different behaviors in the irradiation induced ferromagnetism, the cluster ion can effectively deposit the apparent elastic collision energy at the surface region in the film, which effectively causes the ferromagnetic state at the surface of the films.

The structures of the Fe(2 and 4 ML)/Cu(001) films before and after CO adsorption are revealed by EXAFS. The Fe(2 ML)/Cu(001) film shows an fcc structure before and after CO adsorption. The bare Fe(4 ML)/Cu(001) film also have an fcc structure. However, the CO adsorbed Fe(4 ML)/Cu(001) film changes its structure to the mixture of fcc and strained bcc structures. The strained bcc structure is closely examined, and the shear angle of 10° is most plausible. The relationship between the structure and magnetism has been discussed. The magnetically dead layers have been reported for the CO/Fe(4 ML)/Cu(001) film, and it is concluded that the dead layers correspond to this strained bcc structure. [ABSTRACT FROM AUTHOR]

A twisted magnetic structure in Ni ultrathin films attached to antiferromagnetic FeMn is revealed by a combination of the depth-resolved x-ray magnetic circular dichroism (XMCD) and the polarized neutron reflectivity (PNR) techniques. The depth-resolved XMCD at remanent magnetization shows that the perpendicular magnetization component in the Ni film decreases around the interface to FeMn when the film exhibits perpendicular magnetization, whereas the in-plane component is kept constant through the whole film in the case of in-plane magnetization. Moreover, the PNR data shows that when a weak in-plane magnetic field is applied to a film, which exhibits perpendicular magnetization at the remanent state, an in-plane magnetization component is induced in Ni around the interface to FeMn. These results are reasonably interpreted by assuming that the magnetic moment in the Ni layer is twisted from the perpendicular to the in-plane directions towards the interface to FeMn. Such a magnetic structure is supposed to be induced by a magnetic anisotropy interaction at the interface between ferromagnetic Ni and antiferromagnetic FeMn, which makes the Ni magnetic moment around the interface rotate towards the in-plane direction. [ABSTRACT FROM AUTHOR]

Temperature dependence of remanent magnetization of Ni thin films at the interface to Cu is investigated by means of the depth-resolved x-ray magnetic circular dichroism technique. Although magnetization at the interface is smaller than that in the inner layers, no detectable difference in Curie temperature, at which remanent magnetization vanishes, is found between the interface and the inner layers. In contrast, the magnetization-temperature curves at the interface and in the inner layers show a small difference, which cannot be explained by using a simple mean-field theory if the interface layer is assumed to have the same exchange-coupling constant as that in the inner layers. It is also shown that the critical exponent for the in-plane magnetized film is significantly larger than that for the perpendicularly magnetized film due to the difference in the degree of freedom for the magnetic moment. [ABSTRACT FROM AUTHOR]

High signal-to-background (S/B) ratio depth-resolved soft X-ray absorption spectroscopy (XAS) is achieved by an energy-selective detection of the fluorescence with a diffraction grating at different emission angles. We apply this technique to a Au/FeCo/BaTiO3 thin film, and selectively observe the Fe and Co Lα fluorescences. The S/B ratio for the Co L-edge depth-resolved XAS is then enhanced by nearly two orders of magnitude. We observe the spectra at different probing depths, and find from the layer-resolved analysis that ∼60% of bottom Co is oxidized. A significant improvement in the observation of the buried interface state is thus successfully demonstrated. [ABSTRACT FROM AUTHOR]

The magnetic properties of ferromagnetic Ni thin films grown on a Cu(001) single crystal are modified by the growth of a NiO overlayer, as well as by the voltage application through the NiO/Ni interface. A spin reorientation transition from in-plane to perpendicular magnetization is induced with increasing NiO thickness, and the coercive field significantly increases by further growth of the NiO overlayer. The remanent magnetization of the films is found to be modulated by the voltage application. Moreover, a small exchange-bias effect arising from the ferromagnetic–antiferromagnetic interaction at the interface is observed, and the amplitude of the effect is modified by the applied voltage. [ABSTRACT FROM AUTHOR]

The insertion effect of an interface NiO layer on magnetism in Fe/BaTiO3 is investigated by X-ray absorption spectroscopy (XAS). From X-ray magnetic circular dichroism (XMCD) analysis, the enhancement of remanent magnetization in Fe is observed with increasing NiO thickness. We also find that the NiO layer is partially composed of metallic Ni, and its thickness is estimated to be ∼0.4 nm from the NiO-thickness dependence of the Ni XAS intensity by assuming that Ni is localized at the interface between Fe and NiO. Moreover, extended X-ray absorption fine structure data shows that the Ni–O distance of the interface NiO layer is shorter than that of bulk NiO, which leads to the pseudomorphic growth of NiO on BaTiO3. We thus suppose that the improved Fe growth promoted by the interface NiO layer enhances the magnetic moment in Fe. [ABSTRACT FROM AUTHOR]

We have studied the effect of cobalt substitution in L10-Fe1-xCoxPt films by means of x-ray magnetic circular dichroism (XMCD) and first-principles calculations. The magnetic moments of Fe (~2.5μB) and Co (~1.5μB) deduced using XMCD were almost unchanged upon Co doping, and the net magnetization decreases with increasing Co content. Calculation also showed that the 3d electrons that have been added by Co substitution occupy only spin-down bands. [ABSTRACT FROM AUTHOR]