Oscillatory superconducting transition temperature in YBa2Cu4O8/La2/3Ca1/3MnO3/YBa2Cu4O8 heterostructures

YBa2Cu4O8/La2/3Ca1/3MnO3/YBa2Cu4O8 (Y-124/LCMO/Y-124) heterostructures were prepared by facing-target sputtering technique. The oscillatory behavior of superconducting transition temperature (TC) with the thickness of LCMO (dL) has been observed. The strongest nonmonotonic information in TC-dL curves appears clearly when dL is larger than the critical thickness dLCR. The metal-insulator transition temperature (TMI) can only be detected at dL > dLCR. For LCMO/Y-124/LCMO trilayer films, the TMI has also shown an oscillation with decreasing spacer layer thickness. These kinds of symmetric dependence on the spacer layer in LCMO/Y-124 systems suggest strongly the interplay of ferromagnetic and superconducting couplings.