Kinetics of Magnetization Reversal in Superconductor–Ferromagnet Heterostructures in Longitudinal and Perpendicular Magnetic Fields

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The kinetics of magnetization reversal in LSMO/YBCO hybrid nanostructures in longitudinal and perpendicular magnetic fields is investigated at temperatures above and below that of the superconducting transition. It is shown that, in a perpendicular magnetic field, the presence of the ferromagnetic layer in the structure leads only to an increase in the local pinning of vortices and inhomogeneity of the penetrating magnetic flux due to its dendritic penetration into YBCO. However, in a longitudinal field, various patterns of magnetic-flux penetration into YBCO are observed, which are determined by the magnetic prehistory, i.e., by the type of magnetic-domain structure formed in LSMO after magnetization reversal above the critical temperature of the superconductor. In particular, the longitudinal magnetic field applied to the structure is transformed either to macroscopic droplets with an alternating perpendicular magnetic flux or to extended longitudinal waves of the perpendicular flux, which decay upon propagation deep into the superconductor; i.e., in both cases, vortices and antivortices perpendicular to the superconductor film plane enter the superconductor. The results obtained are qualitatively explained by distortion of the configuration of the longitudinal magnetic field applied to the heterostructure by a ferromagnetic layer deposited under the superconducting layer.