ac susceptibility of a paramagnetic Meissner effect sample

摘要

The dynamic magnetic properties of a granular Bi2Sr2CaCu2O8 sample that displays the paramagnetic Meissner effect have been studied by low field ac susceptibility measurements. The frequency and field dependence of the in-phase and out-of-phase components of the susceptibility show a spontaneous creation of an increasing number of microscopically giant magnetic moments in the sample with decreasing temperature below T-c. The magnetic response of the sample can be explained by a superposition of shielding and flux expulsion from individual grains and a polarisation of spontaneous moments by the applied magnetic field. The polarisation mechanism is the thermal activation over energy barriers separating the up and down directions of the magnetic moments. From our experimental data, the size of the thermally active magnetic moments is estimated to be 10(7)-10(8) mu(B). (C) 1998 Elsevier Science B.V. [References: 29]