Nonlinear effects at the remagnetization of layered high-temperature superconductors with ferromagnetic impurities under the action of a current and an external magnetic field

The processes of remagnetization by the self-field of a transport current in a high-temperature superconductor sample with ferromagnetic particles as defects in the presence of an external magnetic field have been calculated by the continuous Monte Carlo method. A new effect has been detected in the form of a nonlinear $S$-shaped character of current-voltage characteristics of the superconductor-ferromagnet in the external magnetic field. It has been shown that the $S$-shaped feature of the current-voltage characteristic is due to change in the effective interaction of magnetic moments of impurity particles with the vortex system of the superconductor induced by the local remagnetization of ferromagnetic impurities under the action of the self-field of the transport current and by the motion of the magnetic domain and the vortex density domain. The temperature, magnetic field, and imperfection parameters of the sample at which nonlinear effects are manifested have been analyzed. The conditions for the possible generation of radiation in the region of nonlinearity of the current-voltage characteristic have been obtained. The $H-T$ phase diagram of the existence of the instability of the current-voltage characteristic has been plotted.