Gate controllable spin pumping in graphene via rotating magnetization

TL;DR

This paper demonstrates how rotating magnetization in graphene can generate and control pure spin currents, with potential for measurable spin pumping and a spin battery effect in graphene-based heterostructures.

Contribution

It introduces a method to control spin pumping in graphene via gate voltages and rotating magnetization, revealing quantum interference effects and a spin battery phenomenon.

Findings

Spin current can be controlled by gate voltages.

Maximum spin current occurs when one spin species is filtered.

Oscillatory spin current due to quantum interference in F region.

Abstract

We investigate pure spin pumping in graphene by imposing a ferromagnet (F) with rotating magnetization on top of it. Using the generalized scattering approach for adiabatic spin pumping, we obtain the spin current pumped through magnetic graphene to a neighboring normal (N) region. The spin current can be easily controlled by gate voltages and under certain conditions, becomes sufficiently large to be measurable in current experimental setups. In fact it reaches a maximum value when one of the spins are completely filtered due to the vanishing density of states of the corresponding spin species in the ferromagnetic part. Considering an N|F|N structure with a finite ferromagnetic region, it is found that in contrast to the metallic ferromagnetic materials the transverse spin coherence length can be comparable to the length of F denoted by $L$. Subsequently, due to the quantum interferences, the spin current becomes oscillatory function of $JL/\hbar v_F$ in which $J$ is the spin splitting inside F. Finally we show, originated from the controllability of pumped spin into two different normal sides, a profound spin battery effect can be seen in the hybrid N|F|N device.