Spin Transport in Half-Metallic Ferromagnet-Superconductor Junctions

Abstract

We investigate the charge and spin transport in half-metallic ferromagnet ($F$) and superconductor ($S$) nanojunctions. We utilize a self-consistent microscopic method that can accommodate the broad range of energy scales present, and ensures proximity effects that account for the interactions at the interfaces are accurately determined. Two experimentally relevant half-metallic junction types are considered: The first is a $F_1{F}_{2}S$ structure, where a half-metallic ferromagnet $F_1$ adjoins a weaker conventional ferromagnet $F_2$. The current is injected through the $F_1$ layer by means of an applied bias voltage. The second configuration involves a $S{F}_1{F}_2{F}_{3}S$ Josephson junction whereby a phase difference $\Delta \phi$ between the two superconducting electrodes generates the supercurrent flow. In this case, the central half-metallic $F_2$ layer is surrounded by two weak ferromagnets $F_1$ and $F_3$. By placing a ferromagnet with a weak exchange field adjacent to an $S$ layer, we are able to optimize the conversion process in which opposite-spin triplet pairs are converted into equal-spin triplet pairs that propagate deep into the half-metallic regions in both junction types. For the tunnel junctions, we study the bias-induced local magnetization, spin currents, and spin transfer torques for various orientations of the relative magnetization angle $\theta$ in the $F$ layers. We find that the bias-induced equal-spin triplet pairs are maximized in the half-metal for $\theta \approx 90^{\circ }$ and as part of the conversion process, are anticorrelated with the opposite-spin pairs. We show that the charge current density is maximized, corresponding to the occurrence of a large amplitude of equal-spin triplet pairs, when the exchange interaction of the weak ferromagnet is about $0.1E_F.$

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Cited by in corpus (9)

• Cubic spin-orbit coupling and anomalous Josephson effect in planar junctions
• Supercurrent Diode Effect, Spin Torques, and Robust Zero-Energy Peak in Planar Half-Metallic Trilayers
• Tunable planar Josephson junctions driven by time-dependent spin-orbit coupling
• Anomalous supercurrent modulated by interfacial magnetizations in Josephson junctions with ferromagnetic bilayers
• Josephson current through a ferromagnetic bilayer: Beyond the quasiclassical approximation
• Supergap and subgap enhanced currents in asymmetric {S_1FS_2} Josephson junctions
• Charge and Spin Supercurrents in Magnetic Josephson Junctions with Spin Filters and Domain Walls
• Superconducting Vortices in Half-Metals
• Anisotropic angle-dependent Andreev reflection at the ferromagnet/superconductor junction on the surface of topological insulators