# Nanoscale Magnetic Heat Pumps and Engines

## TL;DR

This paper develops a theoretical framework for nanoscale magnetic heat pumps and engines, linking magnetic, thermal, and mechanical effects to enable design of energy conversion devices at the nanoscale.

## Contribution

It introduces a linear response matrix for magnetic nanowires driven by multiple biases and unifies various magneto-thermo-mechanical effects using Onsager's reciprocity.

## Key findings

- Derived an expression for heat-current induced domain wall motion.
- Unified description of Barnett and Einstein-de Haas effects.
- Proposed nanoscale heat pumps and engines based on magnetic domain walls.

## Abstract

We present the linear response matrix for a sliding domain wall in a rotatable magnetic nanowire, which is driven out of equilibrium by temperature and voltage bias, mechanical torque, and magnetic field. An expression for heat-current induced domain wall motion is derived. Application of Onsager's reciprocity relation leads to a unified description of the Barnett and Einstein-de Haas effects as well as spin-dependent thermoelectric properties. We envisage various heat pumps and engines, such as coolers driven by magnetic fields or mechanical rotation as well as nanoscale motors that convert temperature gradients into useful work. All parameters (with the exception of mechanical friction) can be computed microscopically by the scattering theory of transport.