Spin and charge thermopower effects in the ferromagnetic graphene junction

TL;DR

This paper investigates thermoelectric effects in ferromagnetic graphene junctions, revealing how spin and charge currents respond to temperature gradients and external tuning, including conditions for pure spin current generation.

Contribution

It introduces a detailed analysis of spin and charge thermopower effects in ferromagnetic graphene, highlighting the control of pure spin currents via external parameters.

Findings

Charge Seebeck coefficient is an odd function of chemical potential in undoped graphene.

Spin Seebeck coefficient remains an even function regardless of temperature gradient.

Pure spin current can be achieved without charge current by tuning exchange field and gate voltage.

Abstract

Using wave function matching approach and employing the Landauer-Buttiker formula a ferromagnetic graphene junction with a temperature gradient across the system, is studied. We calculate the thermally induced charge and spin current as well as the thermoelectric voltage (Seebeck effect) in the linear and nonlinear regimes. Our calculation revealed that due to the electron-hole symmetry, the charge Seebeck coefficient is, for an undoped magnetic graphene, an odd function of chemical potential while the spin Seebeck coefficient is an even function regardless of the temperature gradient and junction length. We have also found with an accurate tuning external parameter, namely the exchange filed and gate voltage, the temperature gradient across the junction drives a pure spin current without accompanying the charge current. Another important characteristic of thermoelectric transport, thermally induced current in the nonlinear regime, is examined. It would be our main finding that with increasing thermal gradient applied to the junction the spin and charge thermovoltages decrease and even become zero for non-zero temperature bias.