Collapse of the static magnetization in anisotropic hard superconductors

摘要

The suppression (collapse) of the static magnetization of an anisotropic hard superconductor under effect of ac magnetic fields was studied experimentally and theoretically. The measurements were carried out in mutually orthogonal dc and ac: magnetic fields, (H) over right arrow and (h) over right arrow (t). Both fields were parallel to the sample surface. Superconducting Y-123 plate-like single crystals were cut from a textured ingot in such a way that the c axis was in the sample plane. The amplitude of the ac field that suppresses completely the static magnetization was shown to be dependent on the orientation of the magnetic fields with respect to the crystallographic axes of the sample. The dynamics of the collapse of the magnetization was investigated. In some cases, the magnetic moment was found to change non-monotonically with the increase of the amplitude of the ac magnetic field. An unusual phenomenon of the transition of the superconductor from the paramagnetic to diamagnetic state induced by the transverse ac field is discovered. The observed results are interpreted within the framework of the critical state model generalized to the anisotropic case. [References: 19]