Hiromasa Shimojima

Magnetic Shielding Property of Bi(Pb)–Sr–Ca–Cu–O Superconducting Tube

The magnetic shielding property of a Bi(Pb)-Sr-Ca-Cu-O superconducting tube was examined. The measured internal magnetic flux density of the tube, as a function of the applied magnetic field, agreed with the critical state model calculated with the consideration of the hysteresis of the critical current density on the magnetic field.

Magnetic Detector Using Bi-Pb-Sr-Ca-Cu-O Superconductive Film

The Bi-Pb-Sr-Ca-Cu-O film prepared by rf magnetron sputtering was annealed at 780°C for 2 h and 828°-847° for 160 h (two-step annealing). The obtained film made use of a magnetic detector, based on the magnetoresistive effect in the oxide superconductor. Sensitivity to a magnetic field was measured for the obtained films. The 842°C annealed film showed an excellent property as a magnetic detector, and its magnetic field resolution estimated from the sensitivity to the magnetic field and the voltage noise was 1.82×10-6 G/√Hz at 100 Hz. This film was mainly composed of plate like crystals which were partially parallel and partially perpendicularly oriented to the surface of the MgO substrate. It is considered that the grain boundaries between the grains with different crystal axes act as weak links in this compound.

Influence of calcium content on the preparation of the high Tc (110 K class) Bi-Pb-Sr-Ca-Cu-O thin film

The Bi-Pb-Sr-Ca-Cu-O thin films with various Ca/Sr ratios were prepared by r.f. magnetron sputtering using multi-targets (Bi0.5Pb0.50x, CaCu0.750x, SrCu0.75Ox. The high Tc phase (2223 phase) was obtained by firing these films. The film with the highest Ca/Sr ratio (Ca/Sr > 1.0) produced the largest amount of 2223 phase on firing at 850 °C. The highest Ca/Sr ratio (=1.17) film contained 91% volume ratio of 2223 phase compared with the low Tc phase (2212 phase) after 15 h firing. However, the 2223 phase decreased with increasing long-term firing (65 h). The resistance curve of the film with the highest Ca/Sr ratio fired for 65 h showed tailing, until the temperature fell below 20 K, suggesting that this phenomenon was due to the segregation of excess calcium and copper components around the grain, in the amorphous state.

Effect of Al alloy composition on Mechanical Properties of Al2O3 particles reinforced aluminum composite

The chemical composition of an Al alloy will influence the properties of Al alloy matrix composites. In this paper, Al2O3 particles / Al alloy metal matrix composites were made by high pressure infiltration, and the influence of Al alloy chemical composition, especially Si content, on the mechanical properties (strength and toughness) of the Al alloy matrix composites was studied. The Si content of the Al alloy was changed, and other elements were added to examine their influence on the mechanical properties. The results obtained were as follows: when Cu and Ni were added to the Al alloy, the bending strength of the composites was improved at high temperature. Increasing the alumina volume fraction also improved the bending strength. However increasing the Si content decreased the fracture toughness. The possibility of improving heat-resistance of Al2O3 particles reinforced Al composite was found.

Dependence of Magnetic Shielding Property on Critical Current Density

Bi(Pb)-Sr-Ca-Cu-O superconducting tubes with different critical current densities were fabricated to examine the effect of the critical current density on the magnetic shielding property. The shielding magnetic flux density, at which the flux started to penetrate into the tube center, was proportional to the critical current density at zero magnetic field. These experimental results agreed with the calculations based on the critical state model.

Sensitivity to magnetic field for BiSrCaCuO superconductive film

Abstract Bi(Pb)SrCaCuO films prepared by rf magnetron sputtering (film A) and Doctor Blade Casting (film B) were annealed. The films made use of a magnetic detector, based on the magnetoresistive effect in the oxide superconductor. Film sensitivity to a magnetic field was measured. The 842°C annealed film A showed an excellent property as a magnetic detector, and its magnetic field resolution estimated from the sensitivity to the magnetic field and the voltage noise was 1·82 × 10−6G/ √Hz at 100 Hz. This film was mainly composed of plate-like crystals which were partially parallel and partially perpendicularly oriented to the surface of the MgO substrate. It is considered that the grain boundaries between the grains with different crystal axes act as weak links in this compound. However, film B showed high sensitivity to magnetic field, but the output voltage was noisy and the magnetic field resolution was 4·06 × 10−4 G/√Hz at 100 Hz.

Influence of chemical composition of Bi(Pb) system superconductive films on their sensitivity to weak magnetic fields

Abstract The Bi-Pb-Sr-Ca-Cu-O superconductive polycrystal films were prepared by the two-step-annealing of the deposited film on a MgO substrate. Of these films, the low (Bi+Pb) content films showed the highest sensitivity to magnetic fields. On the contrary, the high (Bi+Pb) content films showed the lowest sensitivity. The high sensitivity films indicated the bad c -axis orientation of the grains, but the low sensitivity films indicated the good c -axis orientation. The c -axis length for both of the high T c phase and the low T c phase was separated into two parts. The c -axis of the high T c phase for the high sensitivity films was about 0.01 nm shorter than those for the low sensitivity films. It is postulated that this change of the c -axis length was caused by the increase of d-space in the Bi-O double layer.