Magnetization Control and Transfer of Spin-Polarized Cooper Pairs into a Half-Metal Manganite

Abstract

The pairing state and critical temperature ( T C ) of a thin s-wave superconductor ( S ) on two or more ferromagnets ( F ) are controllable through the magnetization alignment of the F layers. Magnetization misalignment can lead to spin-polarized triplet-pair creation, and since such triplets are compatible with spin-polarized materials, they are able to pass deeply into the F layers and cause a decrease in TC. Various experiments on S/F1/F2 “triplet spin valves” have been performed with the most pronounced suppression of TC reported in devices containing the half-metal ferromagnet (HMF) CrO 2 ( F 2 ) albeit using out-of-plane magnetic fields to tune magnetic noncollinearity [Singh et al., Phys. Rev. X 5, 021019 (2015)]. Routine transfer of spin-polarized triplets to HMFs is a major goal for superconducting spintronics so as to maximize triplet-state spin polarization. However, CrO 2 is chemically unstable, and out-of-plane fields are undesirable for superconductivity. Here, we demonstrate low-field (3.3 mT) magnetization-tunable pair conversion and transfer of spin-polarized triplet pairs to the chemically stable mixed valence manganite La 2 / 3 Ca 1 / 3 MnO 3 in a pseudo-spin-valve device using in-plane magnetic fields. The results match microscopic theory and offer full control over the pairing state.