Koichi Tsukamoto

Magnetoresistance effect in La-A-Mn-O (A = Ca, Ba) thin films synthesized by metal-organic decomposition

Polycrystalline La(0.67)A(0.33)MnO(z) (A=Ca, Ba) thin films were successfully synthesized on quartz substrates by metal-organic decomposition. Some of the La-0.67(Ca0.5Ba0.5)(0.33)MnOz films were deposited on quartz with a SrTiO3 template layer (LCBMT). The porous structure of the films was observed by atomic force microscopy. It was found that all the films showed a broad peak effect of resistance under the zero field, over a temperature range of 77-302 K. Under a 10 kOe field, however, only La0.67Ca0.33MnOz films revealed a broad magnetoresistance (MR) peak. An enhanced MR effect was exhibited at low temperatures in all films, which was related to the porous structure of the films. LCBMT presented larger MR values below 180 K, than the La-0.67(Ca0.5Ba0.5)(0.33)MnOz films without a template layer. The low-field MR effect was observed in all films at 77 K, but it weakened with increasing temperature, and disappeared near room temperature, which was attributed to the offset effect of the thermal hopping of carriers on the tunneling MR at high temperature

Recrystallization and Microstructure in Electrophoretically Deposited Ferroelectric BaTiO3 Films under CO2-Laser Irradiation

Recrystallization of BaTiO3 films deposited electrophoretically on Pt plates was investigated under the irradiation of a CO2-laser beam. Laser irradiation of the films caused significant growth of platelike crystals and strip grains on the surface. Considerable recrystallization occurred in a wide temperature gradient region around the laser-irradiated portions. The laser scanning process is suited for the growth of large grains with preferred orientation. The recrystallized phase of film was the tetragonal one of BaTiO3. Remanent polarization of 4.8 µ C/cm2 and coercive field of 3.2 kV/cm were obtained in the film with 4 µ m thickness.

Characteristics of La–Ba–Mn–O thin films grown by metal-organic decomposition

Abstract La 0.67 Ba 0.33 MnO z thin films were grown by means of metal-organic decomposition (MOD) on quartz substrates. Polycrystalline structure of the films with [202] preferred orientation was shown by X-ray diffraction spectrum. Atomic force microscope images revealed that the films were smoothly grown on the substrates and structural defects such as porosity were displayed in the films. The chemical states of the elements obtained from X-ray photoemission spectra were discussed in detail and oxygen deficiency was observed. Furthermore, the magnetic property and magnetotransport behavior of the films were investigated. The films showed a low ferromagnetic transition temperature ( T c ) of about 265 K due to the oxygen deficiency. A smooth metal–insulator transition peaking at a temperature far below T c presented in the temperature dependence of resistivity under zero field. No magnetoresistance (MR) peak but an enhanced MR effect at low temperature was observed under 10 kOe field. The above magnetotransport behavior was ascribed to the structural defects such as grain boundaries and porosity in the films.

Hardening and microstructure of aluminum metal surface by laser alloying process

Hardening and microstructure of aluminum metal surface with CO2 laser alloying process have been investigated. Mixtures of Al, Ti powder and organic flux used as alloying elements was painted onto the metal surface and irradiated by one step specimen move technique. To address uniformly distribution of the fine dendrite structure and eliminating of many pores occurred within alloyed layer, new complex technique of laser irradiation with ultrasonic radiation methods was attempted together to modify them. Evaluations of the microstructure within the alloyed surface, hardness and tribological properties have been conducted. The alloyed surface consisted of dendrite structures of the Ti3Al and Al-Ti solid solution. The Ti3Al dendrite crystallized leads to adhere effectively to the aluminum phase, and the surface approaches Hv equals 600 kg/mm2 in hardness. As substantial tribological property, the wear resistance of the alloyed specimen to cast iron was around less 1/7 time than that with comparing of Al metal.

New ceramic coating technique using laser spraying process

A new ceramic coating technique using a CO2 laser has been developed. A high power density laser beam passes near the substrate. Coating materials are supplied by an extra-high accuracy powder supply device and pass across the laser beam. The coating materials are melted in the laser beam and deposited on the substrate surface. A YSZ (Yttria Stabilized Zirconia) layer and a LaCoO3 layer are made for high temperature solid oxide fuel cells. The crystal structures of the coated layers are the same as that of the original coating materials. Superconducting BPSCCO ceramic films are also made with this process. The films show super-conductivity with Tc at 81 K. The Jc of the specimen is 440 A/cm2 at 77 K. We can easily handle and arrange not only metal but also refractory materials. By adopting a multi-axis robot and a surface treatment laser technique, the laser spraying method described here makes it possible to produce highly functional and three dimensional parts of devices directly from raw powder materials. Thus the proposed method will open the path to an unexplored field of key production technology.