|
In a superconducting spin switch the transition temperature Tc of a superconductor (S) sandwiched between two ferromagnets (F) depends on the relative orientation of the F layer magnetizations. We report on the superconducting transport properties of FSF triple layers, where F is a Co-Pt multilayer with perpendicular magnetic anisotropy and S is Nb. Due to the high coercive fields of the two F layers, a remanent state with a parallel (P) or antiparallel (AP) orientation of the perpendicular magnetization can be achieved. We provide data to prove that the AP state is a saturated state of the F layers rather than a multidomain state in zero field. Tc is higher for the P state compared to the AP state. Moreover, the resistance close to Tc shows a difference when the magnetic field is reduced to zero from the P or AP state. However, Tc is independent of the magnetization orientation if an insulating barrier is introduced between F and S at each of the two interfaces. These results favor the view that observed changes of the resistance have their origin in the enhanced pair breaking by the diffusion of spin-polarized charge carriers from F into S, in contrast to the stray-field induced mechanism proposed recently for in-plane magnetized multilayers with low coercivity [C. Bell et. al. PRB 74 (2006) 214520, D. Stamopoulos et. al. PRB (2007), in press]. |