CPP magnetoresistance of magnetic multilayers: mean-free- path is not the culprit

Abstract The series resistor and Valet–Fert models widely used to describe the current-perpendicular-to-plane (CPP) magnetoresistances of ferromagnetic/non-magnetic (F/N) metal multilayers were recently claimed to apply only for mean-free paths shorter than layer thicknesses; otherwise the mean-free-path was claimed to be an important length scale in the CPP-MR. Contradicting these claims, we show that the behaviors on which they were based do not change when the mean-free path in the N-layer is reduced from about five times to one-fifth its layer thickness. Part of these behaviors can be ascribed to finite spin-memory-loss (spin-flipping) in the F and N metals and the rest might be due to spin flipping at F/N interfaces.