Magnetism and superconductivity in La0.7Ca0.3MnO3/YBa2Cu3O7−δ superlattices

We report on the magnetic and superconducting properties of ${\mathrm{La}}_{\mathrm{0.7}}{\mathrm{Ca}}_{\mathrm{0.3}}{\mathrm{MnO}}_{\mathrm{3}}{\mathrm{/YBa}}_{\mathrm{2}}{\mathrm{Cu}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{7}}$ (LCMO/YBCO) superlattices. For a constant LCMO layer thickness of 6 unit cells (u.c.), resistance and susceptibility measurements show superconductivity for YBCO layer thickness in excess of 4 unit cells. The critical temperature increases with YBCO thickness, and a $T_c$ of 58 K is found for a YBCO thickness of 10 unit cells. Magnetization measurements show a ferromagnetic transition at 100 K in a $({\mathrm{LCMO}}_{\mathrm{6 u.c.}}{\mathrm{/YBCO}}_{\mathrm{5 u.c.}}{\mathrm{)}}_{\mathrm{15 bilayer}}$ superlattice, and a depressed value of the saturation magnetization of 20 emu cm⁻³. These results are discussed in terms of interface disorder (analyzed by x-ray diffraction and transmission electron microscopy) and of the possible interaction between magnetism and superconductivity.