Yohtaro Yamazaki

Microstructure of electroplated soft magnetic CoNiFe thin films

The microstructural and crystallographic characteristics of electroplated soft magnetic CoNiFe thin films were investigated by transmission electron microscopy. Dark field images showed that the film with fcc-bcc dual crystals has a smaller grain size than the fcc or bcc single phase film. The fcc films were found to have a unique microstructure with twin-like stacking faults with relatively uniform grain size distribution, and such twins were also found in the dual phase films. Some coarse grains were found in the bcc films with a twin-free microstructure. The film prepared from the thiourea bath had a smaller grain size than that of the film from the saccharin bath. It is suggested from the diffraction patterns that the fcc and bcc components of the films are substitutional solid solutions of Co, Ni and Fe. The lattice constants of fcc CoNiFe films are determined by atomic concentrations of the three elements. The crystal structures of bcc films are determined by Fe, and the lattice constants are slightly changed by the incorporation of Co and Ni into the bcc lattice of Fe. The CoNiFe films obtained from saccharin and thiourea baths have different lattice constants, because of different sulfur contents of the films.

Substrate-Dependent Microstructure and Magnetoresistance of La?Sr?Mn?O Thin Films Grown by RF Sputtering

The relationship between the microstructure and the magnetoresistive properties of La–Sr–Mn–O thin films was investigated. La0.76Sr0.24Mn0.98O3-δ films were deposited onto (100) SrTiO3, (100) LaAlO3, (110) sapphire and polycrystalline YSZ substrates by rf sputtering. The films grew epitaxilly on SrTiO3 and LaAlO3 substrates with a large number of defects, whereas in-plane-oriented and nonoriented polycrystalline films with 20–60 nm grains grew on the sapphire and polycrystalline YSZ substrates, respectively. The magnetoresistance ratio (H=0.8 T) of the epitaxial films has a peak at a temperature slightly below the maximum resistance temperature. The resistivity of the epitaxial films was ten times less than that of the polycrystalline films. The polycrystalline films exhibited substantial magnetoresistance ratios over a wide temperature range. The existence of grain boundaries and the preferential in-plane grain orientation were found to be correlated to the resistivity, temperature dependence and low magnetic field sensitivity of magnetoresistance.

Cation order and magnetic properties of double perovskite Sr2FeMoO6

A double perovskite type compound Sr2FeMoO6 was synthesized by a solid-state reaction. The order parameter (x) of Fe and Pt ions on the B sites increased from 68% to 82% and the spontaneous magnetization at 5 K increased from 2.1 to 3.0 μB per formula unit by lowering the calcination temperature from 1100 to 500 °C. The dependence of the spontaneous magnetization on x was discussed using two models considering the local magnetic interactions between ions on the B sites. 57Fe Mossbauer analysis suggested the existence of tiny areas of SrFeO3−δ in Sr2FeMoO6.

Control of domain structures and magnetotransport properties in patterned ferromagnetic wires

Observations of controlled domain structures in zigzag patterned cobalt wires are demonstrated. Distinct domain structures are accessible by changing the orientation of magnetic field using the zigzag geometry, which provides a prospective potential to design the desired magnetic structures. Utilizing the subtle technique, we further throw light on the issue of magnetoresistance induced by the different domain structures. It is found that a negative contribution to the resistance is due to the spin configuration around the corner of the zigzag wires and shows an anomalous maximum around 100 K.

Mixed magnetic phases in (Ga,Mn)As epilayers.

Two different ferromagnetic-paramagnetic transitions are detected in (Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition at a higher temperature results from (Ga,Mn)As cluster phases with [110] uniaxial anisotropy and that at a lower temperature is associated with a ferromagnetic (Ga,Mn)As matrix with 100 cubic anisotropy. A change in the magnetic easy axis from [100] to [110] with increasing temperature can be explained by the reduced contribution of 100 cubic anisotropy to the magnetic properties above the transition temperature of the (Ga,Mn)As matrix.

Proton conductivity of zirconium tricarboxybutylphosphonate/PBI nanocomposite membrane

Abstract The preparation process and proton transport properties of zirconium tricarboxybutylphosphonate Zr(O3PC(CH2)3(COOH)3)2 (Zr(PBTC))/polybenzimidazole (PBI) composite membranes have been investigated with a view to developing a novel electrolyte for direct methanol fuel cells. A compacted Zr(PBTC) powder sample and a Zr(PBTC)/PBI composite membrane with 50 wt.% Zr(PBTC) content show conductivities of 6.74 × 10–2 S cm–1 and 3.82 × 10–3 S cm–1 at 200 °C under a fully humid condition, respectively. Post-sulfonation thermal treatment, which has a great effect on the ligand structure of PBI, gives a marked increase in the conductivity of the membrane by a factor of 2 in the same condition. This effect is mainly attributed to the proton transport via sulfonic acid groups bonded to the PBI unit.

Magneto-optical properties and morphology of particulate film consisting of Bi-YIG coprecipitated particles

Abstract Magneto-optical properties of particulate films containing bismuth yttrium iron garnet small particles were investigated. The small particles with different crystallite sizes were prepared by coprecipitation method and changing heat treatment temperatures from 600° to 725°C. The crystallite size of the particle increased with raising heat treatment temperature and the saturation magnetization showed a maximum for the particles heated at 700°C. Oscillatory behavior of the Faraday rotation of the particulate film was also observed as a function of the heat treatment temperature. This can be well characterized by the magnetization and the absorption coefficient that abruptly increases around 650°C. The increase in the absorption coefficient was due to the change in the size of constituent garnet particles in the film. The magneto-optical properties and the morphology of the particulate films were examined in detail.

The Structure of Electroless Cobalt Alloy Films for Perpendicular Magnetic Recording Media

Two types of electroless Co alloy films, and , were prepared for perpendicular magnetic recording media. The correlation between their structure and magnetic properties was investigated and discussed as a function of film thickness. The magnetic properties of these two types of films showed different patterns of dependence with respect to the film thickness. The Co‐Ni‐Re‐P alloy film gave a higher (perpendicular coercivity) in regions where it was very thin; on the other hand, the Co‐Ni‐Re‐Mn‐P alloy film displayed a lower at the initial film thickness. The composition was observed with AES measurements to be nearly independent of film thickness. The clear columnar structure of both types of films was confirmed by scanning electron microscopy (SEM) and especially by transmission electron microscopy (TEM) observations. Only the reflection high energy electron diffraction (RHEED) patterns for both types of film clearly showed different dependence patterns with respect to the film thickness. The Co‐Ni‐Re‐P film displayed a very highly c‐axis oriented structure even at the initial thin film stage. On the other hand, the Co‐Ni‐Re‐Mn‐P film showed a dependence of the degree of c‐axis orientation on the film thickness, which increased with film thickness. The differences in magnetic properties as a function of thickness were assumed to be due to the degrees of c‐axis orientation and change in magnetic domain structure.

Strain-induced anisotropic low-field magnetoresistance of La–Sr–Mn–O thin films

Sputtered La0.71Sr0.29Mn1.01O3−δ (LSMO) thin films on (001) SrTiO3, polycrystalline yttria-stabilized zirconia (YSZ) and (1120) sapphire substrates demonstrate the distinctive low-field magnetoresistance (MR) correlated with the microstructure and the strain of the films. The epitaxial LSMO film on (001) SrTiO3 shows the in-plane magnetic anisotropy with [110] easy axis and the attendant anisotropic MR. The polycrystalline films on YSZ and sapphire substrates with grain sizes from 20 to 60 nm exhibit different anisotropic feature of transport: the isotropic MR of the film on YSZ and the large anisotropy on sapphire substrates. Moreover, in the (1120) film plane of sapphire substrate, the [1100]SAP magnetic easy axis appears due to a large tensile stress, and the longitudinal MR becomes pronounced along the [0001]SAP hard axis. This implies that the anisotropy of the low-field MR is attributed to the stress induced by the thermal expansion mismatch between film and substrate. These results emphasize tha...

Oxidation behavior of an La-coated chromia-forming alloy and the electrical property of oxide scales

La-coating by electron-beam vacuum deposition was applied to a chromia-forming alloy. The effects of La-coating on oxidation behavior of the alloy and on the electrical property of the oxide scale, thermally grown in solid oxide fuel cell (SOFC) operating atmospheres, were investigated. The elemental analysis results of La-coated specimens indicate that chromium in the alloy is oxidized internally under the La-diffusion region. The electric resistance of the La-coated specimen is found to be lower than that of the uncoated specimen by more than one order of magnitude.