Superconducting and ferromagnetic properties of epitaxial YBa2Cu3O7−δ/La2/3Ca1/3MnO3 bilayers

Perovskite ferromagnetic La2/3Ca1/3MnO3 films with thickness between 22 and 35 unit cells were deposited on single-crystal SrTiO3 substrates with crystal plane orientation (0 0 1) and covered with ∼10 unit cells of superconducting YBa2Cu3O7−δ in order to study their microstructure and physical properties. X-ray diffraction and atomic force microscopy studies showed no dramatic change of the structural and morphological quality of the superconducting top layers with increasing of the thickness of the ferromagnetic layer. Electrical transport and magnetic measurements revealed a strong dependence of both the superconducting transition temperature and the Curie temperature for the onset of ferromagnetic ordering on the thickness of the ferromagnetic layer. Intrinsic phenomena like proximity effect or extrinsic factors like interface strain, interdiffusion of cations between the constituents layers or spin injection from the magnetic into the superconducting electrode are discussed as possible sources of the depression of the critical temperature in these bilayers.