Shin-ichiro Hatta

Highly oriented superconducting Tl‐Ca‐Ba‐Cu oxide thin films with 2‐1‐2‐2 phase

Thin films of the Tl‐Ca‐Ba‐Cu‐O system with 2‐1‐2‐2 phase have been prepared stably on MgO substrates by rf magnetron sputtering and post‐annealing. The post‐annealing of the films was carefully carried out in order to reduce the effect of evaporation of Tl. The annealed films showed a c‐axis‐oriented structure perpendicular to the substrates. The highest zero‐resistance temperature of the films was 102 K. The highest critical current density obtained so far was 1.2×105 A/cm2 at 77 K.

Pt‐coated substrate effect on oxide superconductive films in low‐temperature processing

Excellent films of a high Tc oxide superconductor were easily produced on Pt‐coated substrates at 650 °C. The film superconductivity was significantly improved by the Pt buffer layer. The c axis of the superconductive film was preferentially oriented perpendicularly to the plane with the crystalline oriented Pt coating layer.

Superconducting (Nd,Ce)2CuO4 thin films grown by rf magnetron sputtering

Thin films of an electron‐doped‐type (Nd,Ce)2CuO4 system have been prepared by rf magnetron sputtering and subsequent annealing. The films showed a highly oriented structure with the c axis normal to the film plane. They exhibited superconductivity after the reducing treatment by heating at 800–900 °C in vacuum. The resistivity of the films was fairly low with metallic characteristics, and the sign of the Hall coefficient was negative in the normal state. The sharp superconducting transition with zero resistivity at 22 K was observed for the film of Nd/Ce/Cu:1.855/0.145/1.2.

Superconducting (Nd,Ce)/sub 2/CuO/sub 4/ thin films grown by rf magnetron sputtering

Thin films of an electron‐doped‐type (Nd,Ce)2CuO4 system have been prepared by rf magnetron sputtering and subsequent annealing. The films showed a highly oriented structure with the c axis normal to the film plane. They exhibited superconductivity after the reducing treatment by heating at 800–900 °C in vacuum. The resistivity of the films was fairly low with metallic characteristics, and the sign of the Hall coefficient was negative in the normal state. The sharp superconducting transition with zero resistivity at 22 K was observed for the film of Nd/Ce/Cu:1.855/0.145/1.2.

X-ray photoelectron spectroscopy of Nd2-xCexCuO4-y (x=0 and 0.15) thin films

Electronic structure of Nd2−xCexCuO4−y (x=0 and 0.15) thin films was examined by x‐ray photoelectron spectroscopy. The films were prepared by rf magnetron sputtering and successive annealing under reducing condition (reduction). The reduced films showed semiconducting and superconducting behaviors depending on the value x. The Cu, O, and Nd core‐level spectra revealed that the doped electrons were predominantly in CuO2 plane of the Nd2CuO4 crystal. The Cu core‐level spectra from x=0.15 films before and after the reduction suggested that the reduction added electrons to Cu4s‐O2p extended conduction band, and strengthened Cu O bond covalency to screen the core hole state by mobile itinerant electrons.

Electron Spectroscopy of Nd2-xCexCuO4-y (x=0, 0.15, and 0.23) Thin Films

Electron spectroscopy of Nd 2- x Ce x CuO 4- y ( x =0, 0.15, and 0.23) thin films prepared by rf magnetron sputtering and successive annealing under a reducing condition was carried out. The films showed semiconducting, superconducting, and metallic behaviors according to x . The X-ray photoelectron and Auger electron spectra revealed that the electrons doped by replacing Nd 3+ with Ce 4+ were present in both the CuO 2 plane and the Nd layer of the Nd 2 CuO 4 crystal. The Cu valence was found to be 1+ for the superconducting x =0.15 film by the photoelectron and Auger electron spectra. U dd =9 eV and U pp =6 eV were obtained from the CuL 3 VV and OKVV Auger electron spectra for the x =0.15 film.

Anomalous Magnetization and Magnetoresistance of Fe-Ni Invar under High Magnetic Fields

Magnetization measurements have been made for Fe–Ni Invar alloys in high magnetic fields up to 180 kOe at high temperatures up to 850 K. In contrast to the case of pure Fe and pure Ni, M 2 - H / M curves for Invar alloys are hardly described by Landaus phenomenological equation in a high field region above 100 kOe. Namely, the M 2 - H / M curves are bent upward in high fields. Furthermore, it was observed that the magnetization curve is deviated upward from linearity by applying high fields in a higher temperature region. This additional magnetization over the usual one was reconfirmed by means of the transversal magnetoresistance effect measured with a pulse high field up to 300 kOe. This anomalous magnetization induced by a high field is considered to be due to re-polarization of low spin states of constituent Fe atoms.

X-ray irradiation enhanced critical current density and strong pinning sites created in Gd1Ba2Cu3O7−x thin films

An enhancement of the critical current density (to more than 106 A/cm2 below 65 K) of Gd1Ba2Cu3O7−x superconducting thin films was achieved by X-ray irradiation with oxygen annealing. This process of X-ray irradiation with oxygen annealing introduced stable pinning centers into the crystal and also increased the activation energy from 0.1 eV to 0.25 eV.

Critical Exponents Determined for Nickel from Magnetization Measurement in High Magnetic Fields

Magnetization curves were measured for Ni near and above the Curie temperature in magnetic fields up to 160 kOe. By extrapolating linear parts of ( M 2 - H / M ) curves in a high field region, the critical exponents were estimated without being affected by spin clusters. These values are consistent with those expected from the molecular field theory.

Strongly Induced Perpendicular Anisotropy in Magnetic Thin Films by Micro-Fabrication

Strong perpendicular anisotropy was induced by micro-fabrication in magnetic thin films in which isolated magnetic micro-pillars were regularly formed on the surface. The result indicated that most of the films with in-plane anisotropy may be changed to perpendicularly magnetized recording media.