Magnetic hysteresis in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// magnetometer sense loops

We have measured the magnetic hysteresis of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin-film magnetometer test sample at 77 K for applied magnetic field ramp amplitudes up to 1 mT. The test sample was designed with two distinct SQUID magnetometer input sense loops connected in series with each other and also with an output washer located outside of the magnetic field application region. In addition to permitting fields to be applied to the input loops in the same direction, as in a conventional magnetometer arrangement, this sample design allowed opposing fields to be applied to the loops, providing a measure of hysteresis behavior expected for a gradiometer loop. The fractional hysteresis in the loops for field excursions of 100 /spl mu/T, as encountered for rotation in the Earth\´s field, was 2.1/spl times/10/sup -5/ for the gradiometer mode measurement, and 3.5/spl times/10/sup -4/ for a magnetometer measurement. We found that hysteresis measured with the sample cooled down in a 50 /spl mu/T field was identical to that measured with the sample cooled in "zero field".