Superconducting triplet spin valve

TL;DR

This paper investigates how the critical temperature in superconductor-ferromagnet trilayers varies with magnetization angles, revealing a triplet spin-valve effect and reentrant behavior, advancing understanding of superconducting spintronics.

Contribution

It demonstrates the nonmonotonic dependence of T_c on magnetization angle and predicts a triplet spin-valve effect with reentrant T_c behavior in SFF trilayers.

Findings

T_c varies nonmonotonically with magnetization angle.

Reentrant T_c(lpha) behavior is predicted.

Both standard and inverse switching effects are possible.

Abstract

We study the critical temperature T_c of SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. We demonstrate that T_c can be a nonmonotonic function of the angle \alpha between the magnetizations of the two F layers. The minimum is achieved at an intermediate \alpha, lying between the parallel (P, \alpha=0) and antiparallel (AP, \alpha=\pi) cases. This implies a possibility of a "triplet" spin-valve effect: at temperatures above the minimum T_c^{Tr} but below T_c^{P} and T_c^{AP}, the system is superconducting only in the vicinity of the collinear orientations. At certain parameters, we predict a reentrant T_c(\alpha) behavior. At the same time, considering only the P and AP orientations, we find that both the "standard" (T_c^{P} < T_c^{AP}) and "inverse" (T_c^{P} > T_c^{AP}) switching effects are possible depending on parameters of the system.