High temperature superconductor sensors for low field magnetometry

The nonlinear strong response of high-temperature superconductors immersed in alternating magnetic fields is employed for measurements of very weak DC fields. Even harmonics are generated due to a strong field dependence of the critical current in these materials. A second harmonic signal induced by magnetic flux threading a detection coil yielded a sensitivity to magnetic fields as low as several tenths of a picotesla. For the best bulk sensors, a minimum detectable flux density of 4*10/sup -11/ T was found for S/N (signal/noise)=1.<
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