Quantum dynamics of tunneling between ferromagnets

TL;DR

This paper investigates the quantum tunneling of spin currents between ferromagnets, deriving an effective action and revealing both DC and AC spin Josephson effects influenced by external magnetic fields.

Contribution

It introduces a theoretical framework for spin tunneling in ferromagnetic junctions, demonstrating the existence of a full O(3) symmetric DC spin Josephson current and its conversion to an AC current under magnetic fields.

Findings

Derivation of the effective action for ferromagnetic junctions.

Identification of a DC spin Josephson current with O(3) symmetry.

Prediction of an AC spin Josephson effect induced by external magnetic fields.

Abstract

We study the Josephson-like spin currents between two ferromagnetic metals by deriving the effective action of the junction. A DC spin Josephson current with the full O(3) symmetry is obtained. By the analogy to the superconducting junctions, we have shown that a time-independent uniform magnetic field can serve as the source of the AC spin Josephson effect. That is, the spin current becomes a periodic function of the time with the period proportional to the inverse of the magnitude of the external magnetic field.