Collapse of static magnetization of type II anisotropic superconductors

The effect of suppression of static magnetization (magnetization collapse) of an anisotropic hard superconductor by an alternating magnetic field is studied experimentally and theoretically. The measurements are performed in constant and alternating magnetic fields H and h(t) which are parallel to the sample surface and are mutually orthogonal. Superconducting samples of the Y-123 system are cut from a grain-oriented piece in such a way that the c axis lies in the plane of the plate. It has been established that the amplitude of the alternating field for which the complete suppression of the magnetization occurs significantly depends on the field orientation relative to the crystallographic axes of the sample. The dynamics of the magnetization collapse is studied, and it is established that, in some cases, the magnetic moment varies nonmonotonically with the growth in amplitude h₀ of the alternating field. A peculiar effect of transition (induced by field h(t)) of the superconductor from the paramagnetic into the diamagnetic state is discovered. The results of observations are explained in the framework of the model of critical state generalized to the anisotropic case.