Improvement in sensitivity of novel magnetic sensor using Y-Ba-Cu-O ceramic superconductor film

The authors report an improvement in the sensitivity of a magnetic sensor made of high-T/sub c/ ceramic superconductor. The sensitivity is discussed in connection with the noise measurement of a film element. It is believed that a high sensitivity comparable to that of a high-T/sub c/ SQUID (superconducting quantum interference device) utilizing ceramic materials can be obtained with the present magnetoresistive superconductive element. The magnetic field dependence of the electric resistance of the element at 77 K is shown. The sensitivity as a function of the current is compared for various elements. It is found that the sensitivity of this element is about 100000 times higher than that of a bulk element reported last year. The magnetoresistance at low magnetic field is attributed to the weak couplings between superconductive grains in a ceramic semiconductor. Thus the ceramic superconductor is considered to be a multiconnected Josephson network. The noise is mainly due to the presence of trapped magnetic flux. The reduction of the noise for parallel magnetic field implies the elimination of the trapped flux. Noise measurements are also reported.<>