Influence of magnetic fields on hysteretic ac losses in bulk MgB2 superconductor investigated by using Hall probe ac susceptibility method

We report the results of an investigation of the influence of magnetic fields on hysteretic ac losses in bulk MgB2 superconductor by using Hall probe ac susceptibility. The external magnetic field in this study had an ac part with frequency 10 Hz and magnitude in the range 240-1200 A m-1 and no dc part. We have measured the imaginary part of the magnetic susceptibility and analysed data by using Bean's critical state model of cylindrical geometry for four different temperature values 39.55, 39.51, 39.47 and 39.41 K. The result of this analysis indicates that Bean's model is adequate to explain the experimental findings. Calculated hysteretic ac loss versus applied magnetic field curve is given by using the critical state model. We have also measured the magnetization versus applied magnetic field and determined the first critical magnetic field of a MgB2 sample as 500 A m-1 at 35 K