Critical temperatures in ferromagnetic-superconducting all-oxide superlattices

Ferromagnetic/superconducting superlattices represent a new class of materials with the simultaneous occurrence of superconductivity and ferromagnetism. The mutual interaction of these antagonistic ordering phenomena is of vital fundamental interest and opens novel possibilities for spin-injection devices. Therefore, we systematically studied YBa2Cu3O7-La2/3Ca1/3MnO3 superlattices of different modulation lengths especially with respect to the reduced phase transition temperatures to ferromagnetism and superconductivity, respectively. Conventional models to explain the reduction of T-C and T-Curie fail and novel concepts giving rise to a long-range proximity effect have to be introduced. Furthermore, it is suggested that the pseudogap opening of the YBa2Cu3O7 weakens the innerlayer ferromagnetic coupling of the La2/3Ca1/3MnO3 layers, thus contributing to the reduction of T-Curie.