Daisuke Okai

A crystallization process in an amorphous state under isothermal condition is examined for binary alloys ZrNi and ZrNi2 by differential thermal analysis (DTA). Time dependence of DTA curves is measured at several constant temperatures just below crystallization temperature. The fraction of crystallized volume in amorphous state and its time evolution during isothermal annealing are measured. These data are analyzed by the Johnson-Mehl-Avrami formula. The Avrami exponent is 2.4 +/- 0.1 for ZrNi and 3 similar to 4 depending on the set temperature for ZrNi2. The activation energy for crystallization of amorphous ZrNi and ZrNi2 was estimated by plots of lnt(1/2) vs. 1/T.

We have examined the effect of the loss in the cavity on the measurement accuracy of surface resistance (Rs) of a superconducting thin film using a microstripline resonator. The Rs of a YBCO thin film was measured as a parameter of the height of the cavity's ceiling. The investigation revealed that the loss in the ceiling affected the measurement accuracy of Rs for a comparatively lower ceiling height. However, when the ceiling's height was sufficiently high, the effect was negligible.

The effects of the crystallinity and surface roughness of CeO2 buffer on R-plane Al2O3 substrate on the microwave surface resistance (R-s) of YBa2Cu3Oy (YBCO) thin alms are discussed. We estimated R-s from the transmission characteristics of the microstrip line resonator at 25 K and 6.7 GHz. X-ray diffraction (XRD) of theta-2 theta and phi-scan showed that CeO2 was completely (001)-oriented and in-plane aligned crystal. Fear CeO2 samples with different thicknesses were prepared using identical conditions except for the deposition time, The dependence of RI on CeO2 thickness was measured in the range from 10 mn to 200 nm. The value of R-s was minimum at CeO2 thickness of 100 ma The dependence of R-s vs CeOs thickness was similar to that of the amount of a-axis domains against the thickness The crystallinity of thin CeO2 was poor because the lattice was strongly strained by Al2O3. This affected the quality of the upper YBCO layer. In contrast, thick CeO2 had excellent crystallinity. However, for the thickness of more than 100 nm a drastic change in surface morphology was observed bg atomic force microscopy (AFM), a number of projections appeared on the CeO2 suface. These projections act as nucleation centers for the a-axis domains.

The microstripline resonator (MSR) is used for the measurement of surface resistance of superconducting thin film. We have developed a probe-coupling type MSR. By this method, it is possible to measure the surface resistance of thin film without attaching contacts to the film. To obtain the accurate value of surface resistance, it needs the technique that can measure the quality factor accurately. This paper reports the effect of the cavity's shape on measurement accuracy. For accurate measurement of the surface resistance of superconducting thin film, it was found that the positions of the cavity's ceiling and antennas are important parameters.

Using the microstripline resonator method, we can measure all of the values of the surface resistance. Rs and magnetic penetration depth, λ of superconducting thin film and the dielectric constant, ε_r and dielectric loss, tan δ of dielectric substrate, which are important parameters for designing superconducting microwave passive devices. However, the microstripline resonator method for accurate measurement of the values of the Rs and the λ has not yet been examined systematically. We investigated the effect of the thin film thickness on accuracy of the values of the Rs and the λ. The results show that in order to increase the accuracy of the Rs and the λ, we must take into consideration the thickness of the stripline. The Rs λ of YBCO thin film were measured using the microstripline resonator method. The Rs was 177.2μΩ at 3.9 GHz and at 21K, and the λ(0) was found out to be 0.37μm.