Ferromagnetic clusters and superconducting order in La0.7Ca0.3MnO3/YBa2Cu3O7-delta heterostructures

The existence of magnetic and superconducting order in a [(La0.7Ca0.3MnO3)(100 A)/(YBa2Cu3O7-delta)(100 A)](10) superlattice has been studied by polarized neutron reflectometry, SQUID magnetometry, and resistivity measurements. The magnetization line shapes observed by SQUID magnetometry under zero-field-cooled and field-cooled conditions imply an inhomogeneously disordered magnetic state of the manganite blocks. This is substantiated by resistivity measurements and polarized neutron reflectometry. Resistivity measurements under field-cooled conditions reveal strong perturbations, which imply that the ferromagnetic La0.7Ca0.3MnO3 blocks contain strong magnetic disorder with perturbations coupled to the magnetic order via charge hopping between domains. Polarized neutron reflectometry under zero-field-cooled conditions, below the superconducting transition, reveal a noncollinear ferromagnetic structure, coherent across half the superlattice blocks. Across the superconducting transition, the noncollinear components are perturbed by the superconducting order and attempt to align with the dominant ferromagnetic order. Additionally, the magnetic correlation length increases from half the superlattice structure to a magnetic structure correlated across the complete superlattice. At temperatures above the superconducting transition, the noncollinear magnetic components and the magnetic correlation length relax to the structure observed below the superconducting transition.