Half-Metallic Superconducting Triplet Spin Valve

TL;DR

This paper theoretically investigates a finite size spin valve with a normal metal and a half-metallic ferromagnet, revealing how magnetization orientations influence the superconducting transition temperature and triplet correlations, aligning with experimental observations.

Contribution

It provides a detailed microscopic analysis of triplet correlations and spin currents in a $SF_1NF_2$ spin valve, highlighting the role of half-metallicity and magnetization tilt in enhancing the spin-valve effect.

Findings

Transition temperature $T_c$ varies significantly with magnetization orientation.

Zero energy peaks in local density of states indicate triplet correlations.

Half-metallic ferromagnet enhances spin-valve effects and triplet pairing.

Abstract

We theoretically study a finite size $SF_1NF_2$ spin valve, where a normal metal ($N$) insert separates a thin standard ferromagnet ($F_1$) and a thick half-metallic ferromagnet ($F_2$). For sufficiently thin superconductor ($S$) widths close to the coherence length $\xi_0$, we find that changes to the relative magnetization orientations in the ferromagnets can result in substantial variations in the transition temperature $T_c$, consistent with experiment [Singh et al., Phys. Rev. X 5, 021019 (2015)]. Our results demonstrate that, in good agreement with the experiment, the variations are largest in the case where $F_2$ is in a half-metallic phase and thus supports only one spin direction. To pinpoint the origins of this strong spin-valve effect, both the equal-spin $f_1$ and opposite-spin $f_0$ triplet correlations are calculated using a self-consistent microscopic technique. We find that when the magnetization in $F_1$ is tilted slightly out-of-plane, the $f_1$ component can be the dominant triplet component in the superconductor. The coupling between the two ferromagnets is discussed in terms of the underlying spin currents present in the system. We go further and show that the zero energy peaks of the local density of states probed on the $S$ side of the valve can be another signature of the presence of superconducting triplet correlations. Our findings reveal that for sufficiently thin $S$ layers, the zero energy peak at the $S$ side can be larger than its counterpart in the $F_2$ side.