Competition between the superconducting spin-valve effect and quasiparticle spin-decay in superconducting spin-valves

Abstract

In a ferromagnet/normal metal/ferromagnet spin-valve, spin dependent scattering causes a difference in resistance between antiparallel (AP) and parallel (P) magnetization states. The resistance difference, ΔR = R(AP) − R(P) is positive due to increased scattering of majority and minority spin-electrons in the AP-state. If the normal metal is substituted for a superconductor, the superconducting spin-valve effect occurs: in the AP-state the net magnetic exchange field acting on the superconductor is lowered and the superconductivity is reinforced meaning R(AP) decreases. For current-perpendicular-to-plane spin-valves, existing experimental studies show that the normal state effect dominates (ΔR > 0) over the superconducting spin valve effect (ΔR < 0). Here however, we report a crossover from giant magnetoresistance (ΔR > 0) to the superconducting spin-valve effect (ΔR < 0) in current-perpendicular-to-plane ferromagnet/superconductor/ferromagnet spin-valves as the superconductor thickness decreases below a critical value.