Superconducting triplet spin valve

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 $T_c^\mathrm{Tr}$ but below $T_c^\mathrm P$ and $T_c^\mathrm{AP}$, 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” ($T_c^\mathrm P<T_c^\mathrm{AP}$) and “inverse” ($T_c^\mathrm P>T_c^\mathrm{AP}$) switching effects are possible depending on parameters of the system.