K. Morii

Enhancement of ferromagnetic ordering in dielectric BaFe1−xZrxO3−δ (x=0.5–0.8) single-crystal films by pulsed laser-beam deposition

The effect of Zr substitution on the magnetic and dielectric properties of the BaFe1−xZrxO3−δ epitaxial grown films was investigated. The Zr substitution significantly improved the dielectric properties of the films. In addition to this, the saturation magnetization for the x=0.7 sample was determined to be 0.98μB∕Fen+, in contrast to 0.09μB∕Fen+ for the x=0.5 sample. This implies that the magnetic ordering for the x=0.7 sample has been greatly enhanced, possibly due to the ferromagnetic spin alignment of Fe ions. We will discuss the magnetization behavior in conjunction with the valence state of the Fe ions in the samples.

Formation of the (001) textured Mn5Ge3 phase by solid state reaction of thin multilayered films

Abstract Solid state phase formation by thermal annealing in ion beam sputtered Mn/Ge multilayered films was investigated, as a function of the discharging power of the ion source during sputtering and as a function of the annealing conditions. Films of preferentially (001) oriented Mn5Ge3 were produced upon annealing at 973 K of the multilayered films, expected to be composed of the Mn11Ge8 phase with a preferential (010) orientation developed in the as-sputtered state. It has been shown that the former preferential orientation is induced by the latter. Such inherited orientation relationship has been ascribed to the similarity in the atomic arrangement, within particular crystal planes, between Mn5Ge3 and Mn11Ge8. Phase formation has been discussed in terms of interdiffusion of the layers and in terms of the modified effective heat of formation rule.

Origin of the leakage current in Zr-substituted magneto-dielectric BaFeO3−δ single-crystal films on (0 0 1) SrTiO3 substrates

Epitaxially-grown BFZO thin films with various amounts of Zr content were successfully fabricated on (0 0 1) Nb doped-SrTiO3 substrates using the pulsed laser-beam deposition technique. The Zr substitution caused a substantial decrease in the leakage current density of the films. According to the analysis of the origin of the leakage current behaviour, the samples with x values smaller than 0.7 were found to show Poole–Frenkel (PF) type leakage properties at high electric fields, and the samples with larger x values exhibited Schottky-type behaviour. Regarding the x = 0.7 sample, it was considered that the currents of the PF- and Schottky-type behaviours determined the leakage properties of the samples, resulting in an intermediate state. The observed mechanism change is discussed in conjunction with the electronic band structure change, which may be caused by the increase in the relative amount of Zr ions, as well as by the change in the valence state of the Fe ions associated with Zr substitution.

Martensitic Transformation and Mechanical Behavior of TiNi Shape Memory Alloys after Severe Plastic Deformation

Thermal- and stress-induced martensitic transformation was investigated on TiNi shape memory alloys subjected to severe plastic deformation (SPD) by cold rolling. TEM observation revelaed the sample is a mixture of nanocrystalline and amorphous after 40% cold rolling. DSC analysis suggested that the martensitic transformation was suppressed when the thickness reduction was over 25% reduction. Aging at lower temperatures (573 ~ 673 K, 3.6 ks) restores the phase transformations, but to a limited extent. The stress-strain curves of nanocrystalline/amorphous TiNi are characterized by absence of stress-plateau and small hysteresis.

Surface Amorphization in Intermetallic Compounds by Shot Peening

Surface amorphization by shot peening in intermetallic compounds was examined. The formation of amorphous layer has been verified in Ti-Ni and Zr-Co-Ni alloys. In Ti-Ni alloy, an amorphous phase and nanocrystalline grains were detected by TEM for 120 s peening duration. However, recrystallization and grain growth occurred, when peening duration was up to 400 s. In Zr-Co-Ni alloy, an amorphous phase coexisting with nanocrystalline grains was observed in Zr-37Co-13Ni alloy. For other alloy compositions (Zr-50Co and Zr-50Ni), an amorphous phase was not observed, and nanocrystalline grains were observed. All the observed nanocrystalline grains may be recrystallized from amorphous phase, because their shape was spherical.