Thermodynamics of the heat currents in the longitudinal spin Seebeck and spin Peltier effects

TL;DR

This paper develops a thermodynamic framework to describe heat currents driven by spin currents in Pt/YIG bilayers, deriving conditions for efficient spin Peltier effects and estimating the temperature change scale.

Contribution

It introduces a non-equilibrium thermodynamics approach to analyze spin-induced heat transport and provides criteria for effective spin Peltier effect injection.

Findings

Efficient injection occurs when layer thickness exceeds diffusion length.

The ratio of diffusion length to damping time constants influences effectiveness.

Estimated temperature change per current aligns with experimental observations.

Abstract

We employ the non-equilibrium thermodynamics of currents and forces to describe the heat transport caused by a spin current in a Pt/YIG bilayer. By starting from the constitutive equations of the magnetization currents in both Pt and YIG, we derive the magnetization potentials and currents. We apply the theory to the spin Peltier experiments in which a spin current, generated by the spin Hall effect in Pt, is injected into YIG. We find that efficient injection is obtained when: i) the thickness of each layer is larger than its diffusion length: $t_{Pt} > l_{Pt}$ and $t_{YIG} > l_{YIG}$ and ii) the ratio $(l_{Pt}/\tau_{Pt})/(l_{YIG}/\tau_{YIG})$ is small, where $\tau_i$ is the time constant of the intrinsic damping ($i=Pt, YIG$). We finally derive the temperature profile in adiabatic conditions. The scale of the effect is given by the parameter $\Delta T_{SH}$ which is proportional to the electric current in Pt. Using known parameters for Pt and YIG we estimate $\Delta T_{SH}/j_e = 4 \cdot 10^{-13}$ K A$^{-1}$m$^2$. This value is of the same order of magnitude of the spin Peltier experiments.