Abstract
Odd-frequency triplet Cooper pairs are believed to be the carriers of long-range superconducting correlations in ferromagnets. Such triplet pairs are generated by an inhomogeneous magnetism at the interface between a superconductor (S) and a ferromagnet (F). So far, reproducible long-range effects were reported only in complex layered structures designed to provide the magnetic inhomogeneity. Here we show that spin triplet pair formation can be found in simple unstructured Nb/permalloy ()/Nb trilayers and Nb/Py bilayers, but only when the thickness of the ferromagnetic layer ranges between 140 and 250 nm. The effect is related to the emergence of an intrinsically inhomogeneous magnetic state, which is a precursor of the well-known stripe regime in Py that in our samples sets in at thickness larger than 300 nm.
Highlights
Superconductivity and ferromagnetism are competing phases whose coexistence is unlikely to occur
The domain wall configuration of the structured samples was reproduced by simulations realized with the object oriented micromagnetic framework (OOMMF) software for all the three different regimes [25]
From the analysis of the phase diagrams of the S/F/S trilayers it emerges that a 2D–3D dimensional crossover (DCO) is present only when the thickness of the Py layer is in the emerging stripe-domain (ESD) regime
Summary
Superconductivity and ferromagnetism are competing phases whose coexistence is unlikely to occur. From the case of bulk systems, the coexistence between superconductivity and ferromagnetism may be achieved in artificial superconductor-ferromagnet (S/F) hybrids. In these systems the two antagonistic orderings are confined in spatially separated layers interacting via the proximity effect, which arises when a superconductor comes in metallic contact with a ferromagnet [2]. In this case, the spin-singlet Cooper pairs enter the F-layer and magnetic excitations leak into the S-region across the S/F interface. Since Eex ∼ 1 eV, ξF is only few nanometers
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