The magnetic response of irreversible type-II superconductor slabs subjected to in-plane rotating magnetic field is investigated by applying the circular, elliptic, extended-elliptic, and rectangular flux-line-cutting critical-state models. Specifically, the models have been applied to explain experiments on a PbBi rotating disk in a fixed magnetic field Ha, parallel to the flat surfaces. Here, we have exploited the equivalency of the experimental situation with that of a fixed disk under the action of a parallel magnetic field, rotating in the opposite sense. The effect of both the magnitude Ha of the applied magnetic field and its angle of rotation αs upon the magnetization of the superconductor sample is analyzed. When Ha is smaller than the penetration field HP , the magnetization components, parallel and perpendicular to Ha, oscillate with increasing the rotation angle. On the other hand, if the magnitude of the applied field, Ha, is larger than HP , both magnetization components become constant functions of αs at large rotation angles. The evolution of the magnetic induction profiles inside the superconductor is also studied.

The magnetic behavior of an irreversible type-II superconducting slab under the action of in-plane crossed fields is investigated within both the original elliptic critical-state model and the extended one, which was recently proposed by Clem. In particular, we study the suppression of the remanent magnetization of a PbBi specimen by a sweeping external transverse magnetic field. It is found that both elliptic critical-state models reproduce the main features of available experimental magnetization curves. We also show that the average magnetizations, corresponding to diamagnetic and paramagnetic initial states at a static bias field H z , are asymmetrically reduced by the action of an oscillating transverse field H y . If the amplitude of the oscillations of H y is as large as the first penetration field H P , the resulting state becomes paramagnetic after various cycles of H y . Such a kind of paramagnetism is attributed to the anisotropy, induced by flux-line cutting effects, in the critical current density. In PbBi samples, paramagnetism is expected to be manifest in a wide range of values of the static bias field H z .

Experimental evidence of tremendous magnetic moment dynamical inversion, from metastable trapping state to the state with essentially the same moment oriented in the opposite direction, appearing during giant flux jump connected to thermomagnetic avalanche process in superconducting YBa 2 Cu 3 O 7− δ single crystal, is presented. Magnetization inversion takes place in the system, without thermal contact between sample and sample holder, with a tremendous stored energy once the avalanche process is completed in quasi-adiabatic conditions. A model of magnetic moment inversion, caused by the jump between two metastable states of superconductor with the same energy storage, is presented and discussed in terms of the critical state with peculiar evolution of the critical-current spatial distribution. Importantly, knowledge of conditions of the appearance of such a phenomenon is crucial for applications of bulk superconductors as “permanent” magnets, for example, in superconducting levitation devices, etc.

The evolution of flux distribution in MgB 2 single crystals during their remagnetization was imaged with magneto-optical technique. Meissner holes, formed as the areas where the annihilation of vortices and antivortices takes place, were found at the boundary between oppositely magnetized parts of the crystal. Gradient of magnetic induction in the vicinity of Meissner holes was found to be enhanced. Finger-like structures of convex shape, formed during the penetration of magnetic flux inside the crystal, were observed and explained as an effect of inhomogeneous pinning and demagnetizing field redistribution in the sample.