Spin-current amplification by stimulated spin pumping

TL;DR

This paper introduces two novel mechanisms for amplifying AC spin currents in magnetic materials through stimulated spin pumping, potentially enabling the development of practical spin current amplifiers.

Contribution

It proposes two mechanisms—synchronous and asynchronous—for amplifying spin currents via stimulated spin pumping in ferromagnetic media, a first step towards realistic spin current amplifiers.

Findings

Demonstrates spin current amplification via stimulated spin pumping.

Shows gain saturation profiles analogous to optical amplifiers.

Proposes feasible mechanisms for practical spin current amplification.

Abstract

Stimulated emission is a process during which an atomic system gives away energy to create a coherent photon. It is fundamental to the operation of the optical amplifier. Here we propose two mechanisms for amplifying AC spin currents in a solid-state magnetic medium by a stimulated spin pumping process. The first is synchronous and consists of phase-locked pulses that perturb a precessing magnetic moment. The second is asynchronous and is driven by DC spin currents. The amplification relies on a non-adiabatic interaction taking place in a ferromagnetic medium in which the magnetic moment emits spin angular momentum in the form of spin current before equilibrating with the environment. The pumped spin current amplifies or absorbs the injected AC spin current mimicking the operation of the optical gain medium as readily seen from the gain saturation profiles. The mechanisms we propose are a first step towards a realistic spin current amplifier.