Flux-closure pattern in a two-dimensional NbN-Fe superconductor-ferromagnet nanocomposite: Anisotropy of the angular magnetoresistance

Abstract

The angular dependence of magnetoresistance (MR) of distributed NbN-Fe-NbN Josephson-junctions in the out-of-plane and in-plane magnetic field geometries shows a striking anisotropy on the polarity of the current (I₊/I_-) and its direction with respect to the applied field. The origin of this anisotropy is suggested to be the difference in the degree of spin polarization of electrons injected from Fe nanoplaquettes into the superconducting NbN for I₊ and I_-. Such a conclusion is based on the topography of flux-closure domains in Fe plaquettes. The anisotropy of MR is suppressed at high fields as the flux-closure domains transform into a single-domain structure.