Flux pinning of stress-induced magnetic inhomogeneity in the bilayers of YBa2Cu3O7−δ/La0.67Sr0.33MnO3−δ

Abstract

Elaborately designed bilayers consisting of epitaxial YBa2Cu3O7−δ (YBCO) and La0.67Sr0.33MnO3−δ (LSMO) films were fabricated by pulsed laser deposition with respect to the investigation into magnetic-dependent vortex pinning effect. The improvement in the critical current density and a pronounced upward shift in the superconducting irreversibility line based on magnetotransport measurements are observed when compared to the pure YBCO film, suggesting the enhancement in flux pinning in the studied bilayer. It is believed that the improved flux pinning for YBCO arises from the magnetic inhomogeneity of the underlying LSMO. Magnetization measurements show a nonuniform magnetic state in the LSMO film, most probably being macroscopically phase-separated clusters with ferromagnetic (FM) and anti-FM domains, which can be caused by the epitaxial strain due to the lattice mismatch. Such a magnetic disorder is hardly affected by the external magnetic field, unlike the magnetic disorder induced by the domain structures of FM materials where the magnetic domains naturally disappear as the applied field exceeds the coercive field. Hence, the present magnetic flux pinning may be stiff in the large magnetic fields, showing good prospects for artificial flux pinning enhancements.