Using atomic force microscopy and scanning electron microscopy (SEM), we investigate the correlations between the microstructural defects and the electrical characteristics of the bicrystal grain-boundary Josephson junctions and dc superconducting quantum inference devices (SQUIDs). The structural defects are shown to correlate qualitatively with the characteristics of grain-boundary Josephson junctions patterned on the YBa2Cu3O7−x film. SEM images show that these defects grown on the grain boundary were a few submicron depth of the groove. The low flux noise characteristics were observed when the groove depth was smaller than 18nm in the junctions of the SQUID. The existence of these defects is expected to affect the supercurrent and the motion of the magnetic flux in the films, which dominate the excess noise in the SQUID with bicrystal junctions.

We investigated the relaxation of protons in magnetic fluids using a high-Tc SQUID magnetometer. It was found that the longitudinal relaxation rate, 1/T1, is slower than the transverse relaxation rate, 1/T2, for ferrofluids in the same field. This is due to the fact that the 1/T1 process involves returning the magnetization to the z-direction, which automatically involves the loss of magnetization in the x-y plane governed by the 1/T2 process. Additionally, 1/T1 and 1/T2 at high temperatures are slower than the corresponding relaxation rates at low temperatures, which is due to the enhanced Brownian motion of nanoparticles at high temperatures.

We characterized the current-voltage, voltage-flux, and the field sensitivity of integrated high-Tc series superconducting quantum interference device (SQUID) magnetometers and gradiometers. The series two-SQUID magnetometers shows field sensitivities of ∼30–40fT∕Hz1∕2 at 1kHz and ∼80–100fT∕Hz1∕2 at 1Hz over that of a one-SQUID magnetometer in shielded environment. The field sensitivity of a series two-SQUID gradiometers is ∼60fT∕Hz1∕2cm, while the one-SQUID gradiometer shows a gradient sensitivity of ∼80–150fT∕Hz1∕2cm at 1kHz in an unshielded laboratory environment. The series two-SQUID magnetometers or gradiometers show a significant improvement in flux noises over that of one-SQUID magnetometers or gradiometers.

Despite the significant progress in fabrication methods of step edge, the lack of reproducibility still hinders their use in more complicated systems. To pursue the high reproducibility and quality of step edge for high-Tc superconducting devices, we have developed the technique to fabricate high quality step-edge substrates with arbitrary step angles. We used two steps to improve the step ramp quality substantially. The surface microscopy of step substrates shows high uniformity with respect to any step angle. There are no needles, waves, trenches, cascades, or other flaws on these surfaces. Serial Josephson junctions and superconducting quantum interference device arrays were fabricated onto step-edge substrates. The step-edge devices exhibit excellent results.

Mechanisms of noise increase in direct-coupled high T c superconducting quantum interference device magnetometers exposed to magnetic fields J. Appl. Phys. 90, 4049 (2001); 10.1063/1.1403680Direct-coupled second-order superconducting quantum interference device gradiometer from single layer of high temperature superconductor