Hiroshi Maruyama

Electrophysiological characterization of the tetrodotoxin-resistant Na+ channel, Na(v)1.9, in mouse dorsal root ganglion neurons.

Small dorsal root ganglion neurons express preferentially the Na+ channel isoform NaV1.9 that mediates a tetrodotoxin-resistant (TTX-R) Na+ current. We investigated properties of the Na+ current mediated by NaV1.9 (INaN) using the whole-cell, patch-clamp recording technique. To isolate INaN from heterogeneous TTX-R Na+ currents that also contain another type of TTX-R Na+ current mediated by NaV1.8, we used NaV1.8-null mutant mice. When F− was used as an internal anion in the patch pipette solution, both the activation and inactivation kinetics for INaN shifted in the hyperpolarizing direction with time. Such a time-dependent shift of the kinetics was not observed when Cl− was used as an internal anion. Functional expression of INaN declined with time after cell dissociation and recovered during culture, implying that NaV1.9 may be regulated dynamically by trophic factors or depend on subtle environmental factors for its survival. During whole-cell recordings, the peak amplitude of INaN increased dramatically after a variable delay, as if inactive or silent channels had been “kindled”. Such an unusual increase of the amplitude could be prevented by adding ATP to the pipette solution or by recording with the nystatin-perforated patch-clamp technique, suggesting that the rupture of patch membrane affected the behaviour of NaV1.9. These peculiar properties of INaN may provide an insight into the plasticity of Na+ channels that are related to pathological functions of Na+ channels accompanying abnormal pain states.

Glitch-free X-ray absorption spectrum under high pressure obtained using nano-polycrystalline diamond anvils

Nano-polycrystalline diamond (NPD) [Irifune et al. (2003), Nature (London), 421, 599] has been used to obtain a glitch-free X-ray absorption spectrum under high pressure. In the case of conventional single-crystal diamond (SCD) anvils, glitches owing to Bragg diffraction from the anvils are superimposed on X-ray absorption spectra. The glitch has long been a serious problem for high-pressure research activities using X-ray spectroscopy because of the difficulties of its complete removal. It is demonstrated that NPD is one of the best candidate materials to overcome this problem. Here a glitch-free absorption spectrum using the NPD anvils over a wide energy range is shown. The advantage and capability of NPD anvils is discussed by a comparison of the glitch map with that of SCD anvils.

Novel Magnetic Domain Structure in Iron Meteorite Induced by the Presence of L10-FeNi

Photoelectron emission microscopy has been carried out to study the magnetic properties of iron meteorite associated with the Widmanstatten structure for the first time. A magnetic circular dichroic image reveals a unique magnetic domain structure, resulting in the head-on magnetic coupling over the interface between the α and γ lamellae. Such a magnetic domain structure is unfavorable in any synthetic Fe–Ni alloys. Micromagnetics simulation reasonably explains that the formation of magnetic domains is induced by the L10-type FeNi (tetrataenite) phase segregated at the boundary in the Widmanstatten structure.

Structural, magnetic and electronic state characterization of L1 0-type ordered FeNi alloy extracted from a natural meteorite

To understand the hard magnetism of L10-type ordered FeNi alloy, we extracted the L10-FeNi phase from a natural meteorite, and evaluated its fundamental solid-state properties: sample composition, magnetic hysteresis, crystal structure and electronic structure. We executed multidirectional analyses using scanning electron microscopy with an electron probe micro-analyzer (SEM-EPMA), a superconducting quantum interference device (SQUID), x-ray diffraction (XRD) and magnetic circular dichroism (MCD). As a result, we found that the composition was Fe: 50.47 ± 1.98 at.%, Ni: 49.60 ± 1.49 at.%, and an obvious superlattice peak is confirmed. The estimated degree of order was 0.608, with lattice constants a = b = 3.582 Å and c = 3.607 Å. The obtained coercivity was more than 500 Oe. MCD analysis using the K absorption edge suggests that the magnetic anisotropy could originate from the orbital magnetic moment of 3d electrons in Fe; this result is consistent with that in a previous report obtained with synthetic L10-FeNi.

X-ray magnetic spectroscopy at high pressure: performance of SPring-8 BL39XU.

An X-ray magnetic circular dichroism experiment under multiple extreme conditions, 2 <or= T <or= 300 K, H <or= 10 T and P <or= 50 GPa, has been achieved at SPring-8 BL39XU. A combination of the high-brilliant X-ray beam and a helicity-controlled technique enabled the dichroic signal to be recorded with high accuracy. The performance is shown by the outcome of pressure-induced ferromagnetism in Mn(3)GaC and the pressure-suppressed Co moment in ErCo(2). Two technical developments, a tiny diamond anvil cell inserted into a superconducting magnet and in situ pressure calibration using 90 degrees Bragg diffraction from a NaCl marker, are also presented. X-ray magnetic spectroscopy under multiple extreme conditions is now opening a new approach to materials science.

Ab initio x-ray absorption study of Mn K-edge XANES spectra in Mn3MC (M = Sn, Zn and Ga) compounds

This work reports a theoretical x-ray absorption near-edge structure (XANES) spectroscopy study at the Mn K-edge in several Mn3MC (M = Sn, Zn and Ga) compounds. Comparison of the experimental Mn K-edge XANES spectra and theoretical computations based on multiple scattering theory shows that standard single-channel calculations are not able to reproduce the experimental spectra. The comparison between experimental data and ab initio computations indicates the need to include the charge transfer and hybridization between the absorbing Mn atom and the two nearest neighbour C atoms.

Relationship between XMCD and molecular field in rare-earth (R) transition-metal (T) intermetallic compounds

This work reports an x-ray magnetic circular dichroism (XMCD) study performed at the rare-earth L2,3xa0edges in several rare-earth transition-metal RT2 compounds (T = Fe, Co and Al). The transition metal contributes to the XMCD of the rare earth recorded at the L2xa0edge while no influence is detected at the L3xa0edge. This contribution shows the same spectral shape for both light and heavy rare earths and its amplitude reflects the sign and the magnitude of the magnetic moment of the transition metal. The results here presented point out that this contribution is associated with the molecular field due to the transition metal acting at the rare-earth sites.

Relationship between hydriding and Nd magnetic moment in Nd2Fe14B

We present an x-ray magnetic circular dichroism (XMCD) investigation performed at the Fe K edge in the intermetallic Nd2Fe14BHx and Y2Fe14BHx compounds with controlled hydrogen content. The present study clearly reveals that hydrogen exerts an appreciable influence on the electronic structure of the whole system, and in particular on the rare-earth sublattice. The combined study of both magnetization and XMCD indicates that the magnetic moments of Nd decrease upon hydrogen uptake.

Direct metallographic analysis of an iron meteorite using hard x-ray photoelectron emission microscopy

The local structure of an iron meteorite was analyzed using photoemission electron microscopy (PEEM) and hard x-rays. The x-ray absorption fine-structure spectrum was obtained for each pixel in the PEEM image. The spectrum provides a wide variety of information, e.g., chemical composition, electronic structure, and lattice structure, in the interface region of the Widmanstatten structure. The shape of the absorption edge and the radial distribution function indicate that the structural phase changes from body- to face-centered cubic phases as the Ni composition at the interface is increased. The use of PEEM and hard x-rays is an attractive approach for local structure analysis.

Orbital contribution to perpendicular magnetic anisotropy in Co80Pt20 thin films

We have measured x-ray magnetic circular dichroism spectra at the Co and Pt L2,3-edges in Co80Pt20 perpendicular magnetization films, wherein the uniaxial magnetic anisotropy constant, Ku, significantly increases with decreasing film thickness, δ, and reaches 1.7×107u2002erg/cm3 for δ=3u2002nm. The anisotropy of the orbital magnetic moment (AOM) was estimated as a function of δ, and the relationship between AOM and Ku is discussed. When the thickness was reduced, the AOM for Pt 5d was nearly constant, whereas a weak increase was observed for Co 3d. Both AOMs are small in contrast to the large Ku, and any proportionality between AOM and Ku was hardly recognized. This result indicates that a large AOM is not always a necessary and sufficient condition for the appearance of perpendicular magnetization.