Tadataka Morishita

Improvement of YBa2Cu3Ox Single-Crystal Surface by Chemical Etching

The single-crystal YBa2Cu3Ox (YBCO) surface presents precipitates that aggregate to form a very thin damaged layer on the surface after mechanical polishing and thermal annealing. The damaged layer was removed by dipping it into a chemical etchant, HCl/methanol. After applying the etching process, YBCO(001) surfaces exhibited a well-defined step-and-terrace feature with unit-cell step height. No precipitates were observed from the etched substrates after annealing. Homoepitaxial films on etched substrates grew with unit-cell-high steps and step-edge facets, while those on as-polished substrates exhibited a grain structure with rough edges.

Changes of Structure and Magnetization of Amorphous Rare Earth-Transition Metal Films by Annealing

Magnetization (M) and X-ray diffraction patterns of amorphous Gd–Tb–Fe films were measured. The film annealed at 330°C for 3 hours under a pressure of low vacuum (1×10-3 Torr~1×10-2Torr) showed X-ray diffraction peaks corresponding to bcc Fe and oxides of rare earth metals, and its M increased. We concluded that these results and the irreversible increase of M at temperatures higher than 200°C are caused by clustering of Fe due to immiscibility of Fe with selectively oxidized rare earth metals. To determine the exact crystallization temperature of amorphous RE-TM films, oxidation of the films must be carefully avoided.

Sputtering system for the preparation of compositionally modulated films

A novel sputtering system that was specially designed for synthesizing compositionally modulated films (CMFs) has been produced. In this system, substrates remain above one of two targets during deposition; the substrate positions and deposition periods are computer controlled. Periodic structures in Fe/SiO2 CMFs prepared by the system have been investigated by X-ray diffraction and were found to be well-defined.

Effects of Seed Layer on YBa2Cu3Ox Films Grown by Liquid Phase Epitaxy

Crack-free YBa2Cu3Ox (YBCO) films were grown by liquid phase epitaxy (LPE) on MgO(100) substrates with a YBCO seed layer. The crystalline property of LPE was crucially dependent on that of the seed layer. On the purely c-axis-oriented seed layer, reasonable YBCO films were grown with a full-width at half maximum of the (005) reflection rocking curve, Δω, of 0.07°. In the case of the seed including an a-axis-oriented grain, the value of Δω of LPE films was poor in reproducibility and larger than 0.1° on average. For the a-axis-oriented seed, no YBCO films grew under the growth conditions in this study. X-ray topographic observations revealed that the crystalline quality of MgO substrates limited the Δω of LPE films grown on them.

Magnetic Properties of Compositionally Modulated Fe/SiO2 Films

Compositionally modulated Fe/SiO2 films prepared by sputtering method show a well-defined multilayer structure. Magnetization of Fe/SiO2 films has been studied by a vibrating sample magnetometer. Magnetization of Fe layers decreases gradually with the decrease of Fe thickness (dFe) in the range of dFe smaller than 100 A. However, even when the Fe layer is thinner than monolayer thickness, it shows ferromagnetic behavior at 77 K. Moreover, an Fe layer in a (Fe 1.5 A/SiO2 28.9 A) film has an easy axis of magnetization normal to the film plane.

Observation of Adiabatic Spin Reorientation in ErCrO3

The spin-reorientation (SR) phase transition has been induced by cooling in an adiabatic demagnetization process just above the critical temperature. The magnetic phase diagram and the isentropic curves are presented in a temperature vs field coordinate. By using a change in optical absorption spectra at SR, transient phenomena have been observed. The nucleation rate and the volume fraction of the new phase during SR are determined by a degree of under-cooling and the latent heat at SR which raises the temperature of the thermally-isolated spin system.