Magnetic coupling in superconducting spin valves with strong ferromagnets

Abstract

We investigate the magnetotransport behavior of ferromagnet (F)/superconductor/ferromagnet trilayers made of ferromagnetic Ni80Fe20 (Permalloy, Py) and superconducting Nb for temperatures both above and below the superconducting transition temperature Tc. In such devices, and for weak ferromagnets, Tc depends on the relative magnetization directions of the two F layers in such a way that TcP of the parallel (P) alignment is lower than TcAP of the antiparallel (AP) alignment (the so-called superconducting spin-valve effect). For strong magnets, the suppression of Andreev reflection may alter this picture, but also stray field effects become important, as is known from earlier work. We compare large-area samples with microstructured ones, and find blocklike switching in the latter. We show this not to be due to a switch between the P and AP states, but rather to dipolar coupling between domains which are forming in the two Py layers, making a stray-field scenario likely. We also present measurements of the depairing (critical) current Idp and show that a similar depression of superconductivity exists far below Tc as is found around Tc.

Source-reported materials — not catalogue approval

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