Ultra-low DC Magnetic Field Detection Using Ceramic Superconductors

In the present study, the linear behavior of the second harmonic signal generated by application of very low DC magnetic fields to the polycrystalline bulk high-T (c) superconductors has been examined. The amplitude of AC field, H (ac) , intergranular first critical field, H (1cJ) , and minimum field required for the magnetization of specimen as a whole, H (au), were determined and a special coil design has been presented. The results reveal that the second harmonic signal varies linearly with the applied DC field in the -0.1 Oe to 0.1 Oe range. Additionally, detection of ultra-low DC fields as small as 5 nT has been achieved. Repeatability and reproducibility tests were performed and the resultant data have been found to be consistent. In the light of our study, a commercial magnetometer can be produced to be utilized in successful detection of very low magnetic fields.