Sound magnetometer noise measurements on YBa sub 2 Cu sub 3 O sub 7 thin films and input coils

This paper reports on a SQUID magnetometer system incorporating a Nb-based conventional SQUID operating at 4.8 K used to measure the magnetic field noise from high-T{sub c} input coils and unpatterned films at 77 K. The system allows for the rapid measurement of relatively large regions of high-T{sub c} material. The results on numerous coils and films show the noise decreasing as a function of increasing film critical current density at 77K. High-T{sub c} films with J{sub c}(77K) = 3 {times} 10{sup 6} A/cm{sup 2} appear suitable for use as input coils in SQUID magnetometer applications requiring low noise at frequencies down to 1 Hz.