Nonlinear response in thin film magnetometer sense loops at 77 K

The onset of nonlinear response to applied magnetic field in GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film magnetometer sense loops was measured in equipment performing at 77 K. As the magnetic field applied to the magnetometers was ramped, the output magnetic flux of the sense loops was monitored with a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// DC superconducting quantum interference device flip-chip coupled to the loop sample's output washer. In experiments devised to minimize circulating current in the magnetometers, nonlinear onset fields ranging from 26 to 120 /spl mu/T were measured for samples having linewidths ranging from 20 to 800 /spl mu/m. The loops also exhibited hysteresis in conjunction with the nonlinear behavior. These results indicate that nonlinear hysteresis is an issue for magnetometer loops operating in the Earth's field.< >