Giant magnetoresistance in hybrid superconductor/ferromagnetic sandwich heterostructures

The perpendicular electron transport through a ferromagnetic bilayer (F-1/F -2) in contact with a superconductor (S) was investigated theoretically. Th e conductance is calculated in the Kubo formalism with Green functions foun d as the solutions of the Gorkov equations. It is shown that the giant magn etoresistance (GMR) defined as the relative difference in conductivity betw een the parallel and antiparallel alignments of the magnetizations in Fl an d Fz behaves differently in the ballistic and diffusive regimes. In the for mer case, the GMR amplitude can be fairly large, whereas in the latter case , it almost vanishes, The interpretation of this behaviour is given by comp aring the contributions to the total resistance of the Andreev reflection a t the F-1/S interface and the usual quantum reflection at the F-1/F-2 inter face.