Structure and magnetic characterization of La0.67Sr0.33MnO3/YBa2Cu3O7 superlattices

Abstract

Oxide multilayers composed of ferromagnetic metallic layers of La0.67Sr0.33MnO3 (LSMO) and superconducting cuprate YBa2Cu3O7 (YBCO) were grown on LaAlO3 substrates by high-pressure dc sputtering. We have investigated the structural, transport, and magnetic properties of a series of samples in which the LSMO layer thickness is fixed at eight unit cells and that of YBCO varied from one to six unit cells. The superconducting transition temperature Tc0 determined from the resistance measurement is higher than the temperature of the onset of the diamagnetic response Td0. This result is discussed in the frames of the model proposed by E. B. Sonin and I. Felner [Phys. Rev. B. 57, R14000 (1998)] for a ferromagnetic superconductor. The model suggests the presence of the spontaneous vortex phase in the temperature interval Td0<T<Tc0 without an external magnetic field.