Asymmetric superconducting spin valves based on the Fe/V layer system grown on MgO(100)

We studied asymmetric superconducting spin valves with the layer sequence V/Fe/V/Fe/CoO, grown on MgO(100). These thin film heterostructures exhibit a superconducting spin valve (SSV) effect, that is, a difference, Delta T-s, between the superconducting transition temperatures Ts with the magnetization directions of the two Fe layers oriented antiparallel and parallel. For pure Fe layers in the SSV we observe a maximum shift Delta T-s D = 24 mK. On replacing the Fe layers with FeV alloy layers, the SSV effect was increased to a maximum value of Delta T-s = 35 mK. This is one of the largest shifts observed in SSV devices up to now, but still an order of magnitude smaller than the SSV effect observed in V layers grown on epitaxial Fe/V superlattices previously. Our results suggest a dominant importance of the Fe/V interface quality for the amplitude of the SSV effect.