  In the present work we study experimentally the influence that the domain
structure of a fer- romagnet (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
struc- ture of the FM promotes the nucleation of superconductivity, while its
monodomain state strongly suppresses it. Our experimental findings support
recent theoretical studies proposing that when an inhomogeneous exchange field
is offered by the FM to the SC the superconducting pairs are not susceptible to
pair-breaking.
