Abstract:

In the present work we study experimentally the influence that the domain structure of a ferromagnet (FM) has on the properties of a superconductor (SC) in bilayers and multilayers of La0.60Ca0.40MnO3/Nb and FePt/Nb proximity hybrids. Specific experimental protocols that were employed in the performed magnetization measurements enabled us to directly uncover a generic property of FM/SC hybrids: In the absence of an external magnetic field, the multidomain structure of the FM promotes the nucleation of superconductivity, while its monodomain state strongly suppresses it. Our experimental findings support recent theoretical studies [A. I. Buzdin and A. S. Mel'nikov, Phys. Rev. B 67, 020503(R) (2003); T. Champel and M. Eschrig, Phys. Rev. B 71, 220506(R) (2005)] that suggest the formation of the so-called domain-wall superconductivity and propose that when an inhomogeneous exchange field is offered by the FM to the SC the superconducting pairs are not susceptible to pairbreaking. In contrast, when magnetic homogeneity is restored in the FM the SC's properties are strongly suppressed.