Enhancement of the superconducting transition temperature by an external magnetic field parallel to the plane of La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 trilayers

We investigate the superconducting transition temperature of epitaxial La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 (LSMO/YBCO/LSMO) trilayers as a function of the magnetic field parallel to the layer structure. In these structures, the magnetic moment of the half-metallic ferromagnet LSMO is parallel to the plane of the film. The coercivity- and saturation field of the top and bottom LSMO layer could be independently tuned by adjusting their thickness. The application of a magnetic field increased the superconducting transition temperature by about 1.6 K with respect to the demagnetized state of the LSMO. Three possible mechanisms of the enhancement are considered. These are the stray fields due to domain walls, spin polarization of the current, and the formation of an odd triplet superconducting state.