Dissipationless Spin Current between Two Coupled Ferromagnets

TL;DR

This paper introduces a universal principle where misaligned magnetic orders in coupled ferromagnets generate a dissipationless spin current, analogous to the Josephson effect, applicable to metals and insulators.

Contribution

It establishes a general, scattering-independent principle for dissipationless spin currents between ferromagnets, extending across metallic and insulating systems.

Findings

Dissipationless spin current flows between misaligned ferromagnets.

The principle is analogous to the Josephson effect.

A static magnetic field can control and stabilize the spin current.

Abstract

We demonstrate the general principle which states that a dissipationless spin current flows between two coupled ferromagnets if their magnetic orders are misaligned. This principle applies regardless the two ferromagnets are metallic or insulating, and also generally applies to bulk magnetic insulators. On a phenomenological level, this principle is analogous to Josephson effect, and yields a dissipationless spin current that is independent from scattering. The microscopic mechanisms for the dissipationless spin current depend on the systems, which are elaborated in details. A uniform, static magnetic field is further proposed to be an efficient handle to create the misaligned configuration and stabilize the dissipationless spin current.