Surface Structure and Transport Properties ofYBa2Cu3O7-δUsingLa2/3Ca1/3MnO3as Buffer

The YBa2Cu3O7-δ(YBCO) ultrathin films were prepared by off-axis rf magnetron sputtering on SrTiO3(STO) substrate with a 300-Å-thick La2/3Ca1/3MnO3(LCMO) buffer layer. At low temperature, the magnetism of the LCMO buffer layer seemed to be screened by the epitaxial YBCO layer with a thickness of more than about 125 Å. A remarkable magnetoresistance (MR) ratio was obtained for thinner YBCO cap layer. The superconducting transition temperature,Tc, decreases with decreasing YBCO thickness and disappears at the thickness of less than 85 Å. X-ray diffraction (XRD) was used to characterize the quality of the buffer and epitaxial films. The out-of-plane lattice parameters for both buffer and epitaxial layer varied monotonically. The surface structures of the buffer and the epitaxial YBCO films were characterized by atomic force microscopy (AFM). Interfacial diffusions for cations such as Y, Cu, La, Ca and Sr were deduced from Auger electron spectroscopy (AES). The larger diffusion length was found at the interface between YBCO and LCMO, which may relate to the suppression of superconductivity and magnetoresistance.