Hideo Itozaki

Step-edge junction of YBCO thin films on MgO substrates

The authors have studied the microstructure of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) thin films epitaxially grown on MgO

NDT of high speed fine particles by high Tc SQUID

We detected moving magnetized fine particles with high Tc SQUIDs. The output signals of SQUIDs were investigated with various particle speeds. It was found that the signal decreases less than 20% with an increase of particle speed from 10 to 500 m/min. An iron particle of 50 /spl mu/m diameter could be detected by the SQUID. The high Tc SQUID had a trilayered 15-turn flux transformer. It has a magnetic field resolution of 48 fT Hz/sup -1/2/ at white noise level and a magnetic field capture area of 2.7 mm/sup 2/.

Properties of high Jc BiSrCaCuO and TlBaCaCuO thin film

Abstract BiSrCaCuO thin films were prepared by an RF magnetron sputtering. We obtained a c-axis oriented polycrystal with many intergrowth layers. This film has high Jc of 3.4MA/cm 2 at 77.3K. TlBaCaCuO thin films were also prepared by the sputtering. It was a c-axis textured polycrystalline thin film. Its Tc(R=0) and Jc was 115K and 3.2MA/cm 2 , respectively.

High Jc superconducting thin films prepared by sputtering

Abstract REBaCuO (RE: Rare earth element) high Jc superconducting single crystalline films were grown on MgO (001) substrates by a magnetron sputtering. The critical current density Jc of the HoBaCuO film was 3.53 million A/cm2 at 77.3K. Even under the influence of a magnetic field of 1.0T, Jc was sustained at more than 1.5 million A/cm2 at 77/3K. X-ray, RHEED and SEM analyses showed that these films are epitaxially grown single crystals with extremely smooth surface.

Flux trapping of High Tc dc SQUID

Flux trapping, which occasionally occurs when a high-Tc SQUID is cooled, degrades the performance of the SQUID. We have investigated the flux noise (1-1kHz) of YBCO dc-SQUIDs cooled in static magnetic fields of 0.1µT to 1mT. It was not affected for magnetic fields less than 0.5 µT corresponding to about 1/100 of the ambient earth magnetic fields. For magnetic fields of more than 1µT, the flux noise at low frequency (1 Hz to 100Hz) increased. The white noise level increased for magnetic fields over 5µT (= about 1/10 of the ambient earth magnetic fields). We observed random telegraphic signal noise in fields over 5011T (= about the ambient earth magnetic fields); excess noise of low frequency markedly increased by a factor of 20000 for this field. To obtain good SQUID performance, it is necessary to cool it under a magnetic field of less than 1/100 of the ambient earth magnetic field.

Properties of High Jc BiSrCaCuO Thin Film

BiSrCaCuO thin films were grown on MgO substrate by an RF magnetron sputtering. Its Jc was 1.9 million A/cm2 at 77.3K and 21 million A/cm2 at 40K. Anisotropic degradation of Jc was observed. In the most severe case, Jc decreased to 0.1 million A/cm2 as applied magnetic field increased to only 0.5 Tesla. X-ray analysis showed that this film consists of almost single high Tc 2223 phase with c=37.2A. RHEED, SEM and TEM observation showed that this high Jc thin film was c axis oriented polycrystalline. The grain boundaries and stacking faults were not barriers for supercurrent to flow but they might act as pinning places for magnetic flux.

Large Washer SQUID

Focussing effect of YBa2Cu3O7−y large washer SQUID and flux shielding plates were studied. Optimizing the hole size of the shielding plates, the flux capture area was improved up to 60% of the theoretical value. The field resolution was 370fT/Hz1/2 at 10Hz. We have developed a 16-channel high-Tc SQUID magnetometer system, and demonstrated that the 16 channel magnetocardiogram can be obtained. The devices used in this system were sealed by epoxy resin; there were no significant degradation of the SQUID performances after the heat cycles (room temperature to 77K) of 50 times.

Microwave Propagation on High-J c YBCO Transmission Lines

We have prepared YBCO superconducting transmission lines on the substrates of a MgO single crystal and have studied the propagation of microwave signals from 200MHz to 20GHz on these lines. The transmission lines are co-planar type and are 0.5μm thick, 30–100μm wide, and 12mm long. Their critical current densities which were directly measured through the whole line (12mm long) were more than 105A/cm2 at 77.3K. The transmission properties of the YBCO superconducting co-planar lines were measured by a network analyzer. The results were compared with those of Al transmission lines. The transmission losses on the YBCO co-planar line (30μm wide) were less than 0.5dB for frequencies up to 9GHz. They are lower than those on the equivalent Al line on a MgO single crystal at 77.3K.

YBa2Cu3O7−y SQUID with Step-Edge Junctions

YBa2Cu3O7− junctions were fabricated. We have studied characteristics of the SQUIDs with different inductances. The flux transfer function was affected significantly by the SQUID inductance. The minimum energy sensitivity at 10Hz of 3.3 × 13.10−29J/Hz was obtained at the SQUID with inductance of 40pH. The superconducting focussing plate was applied to the SQUID to enhance the magnetic field sensitivity. The flux capture area increased by a factor of 3.6 and was 1.8 × 10-8m2. The flux noise Sϕ 1/2 at 10 Hz was 3.4 x× 10−5ϕ0/Hz1/2, corresponding to 3.7pT/Hz1/2.

Resistive Behavior of High Tc Superconducting Thin Film in Magnetic Field

We have measured the temperature dependence of resistance for epitaxial and polycrystalline YBCO thin films in a magnetic field. The resistive behavior of the epitaxial thin film could be explained by the flux creep model. The pinning potential estimated from that model had strong anisotoropy and this anisotropy was consistent with that of the coherence length. On the other hand, the resistive behavior of the polycrystalline thin film could not be explained by the flux creep model. It was suggested that the broadening of the resistivity for the polycrystalline thin film is caused by weakly linked grain boundaries.