Superconducting spin valves based on epitaxial Fe/V superlattices

Abstract

In superconducting spin valves of the type S/F1/N/F2 or F1/S/F2 with a superconducting layer S, two ferromagnetic layers F1 and F2, and a normal metallic layer N, the superconducting transition temperature TS depends on the relative magnetization direction of the ferromagnetic layers F1 and F2. The difference of the transition temperature ΔTS=TsAP−TsP with the magnetization direction of F1 and F2 either antiparallel or parallel is called the superconducting spin valve effect. We have prepared both types of spin valves by growing Fe/V thin-film heterostructures with epitaxial quality on MgO(001) substrates. In the S/F1/N/F2-type spin valves the ferromagnetic layers were the first two Fe layers of a [Fe/V] superlattice coupled antiferromagnetically via the interlayer exchange interaction. Here we observed a superconducting spin valve shift of up to ΔTS≈200 mK when aligning the sublattice magnetization in an external magnetic field. In the F1/S/F2-type spin valves the ferromagnetic layer F1 was either a [Fe/V] or a [FexV1−x/V] superlattice, the F2 layer was a Fe-, a Co-, or a FexV1−x film. Using weakly ferromagnetic FexV1−x alloy layers as F1 and F2 we find a spin valve effect of up to ΔTS≈20 mK, which is more than a factor of 2 larger than reported in the literature before for spin valves with comparable transition temperatures. Our results indicate that a high interface transparency and a large superconducting correlation length are prerequisites for the observation of a sizable superconducting spin valve effect.

Source-reported materials — not catalogue approval

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