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YBa2 Cu4 O8 /La0.67Ca0.33MnO3/YBa2 Cu4 O8 (YBCO/LCMO/YBCO) trilayer films were prepared by magnetron facing-target sputtering. For the first time, the oscillatory behaviour of superconducting transition temperature TC,ON with the thickness of LCMO (dL) has been observed. The strongest nonmonotonic information in the TC,ON-dL curves appears clearly when dL is larger than the critical thickness dLCR. The metal-semiconductor transition temperature can only be detected at dL ＞ dLCR. The dependence on the ferromagnetic spacer layer in YBCO/LCMO/YBCO systems suggests strongly the interplay of ferromagnetic and superconducting couplings.