Spincaloric properties of epitaxial Co$_2$MnSi/MgO/Co$_2$MnSi magnetic tunnel junctions

TL;DR

This paper introduces a novel approach to calculating spincaloric properties in magnetic tunnel junctions, accounting for temperature-dependent effects and interface conditions, with potential applications in thermally operated memory devices.

Contribution

A new method for evaluating spincaloric properties that surpasses linear response limitations and includes temperature-dependent chemical potentials and finite-bias effects.

Findings

Large spin-dependent Seebeck coefficient of -65 μV/K at room temperature.

Interface termination significantly influences spincaloric properties.

Method enables tailored thermoelectric responses in magnetic tunnel junctions.

Abstract

The electronic transport and spincaloric properties of epitaxial magnetic tunnel junctions with half-metallic Co$_2$MnSi Heusler electrodes, MgO tunneling barriers, and different interface terminations are investigated by using first-principles calculations. A new approach to spincaloric properties is presented that circumvents the linear response approximation inherent in the Seebeck coefficient and compared to the method of Sivan and Imry. This approach supports two different temperatures in the two electrodes and provides the exact current and/or voltage response of the system. Moreover, it accounts for temperature-dependent chemical potentials in the electrodes and finite-bias effects. We find that especially the former are important for obtaining qualitatively correct results, even if the variations of the chemical potentials are small. It is shown how the spincaloric properties can be tailored by the choice of the growth conditions. We find a large effective and spin-dependent Seebeck coefficient of $-65$ $\mu$V/K at room temperature for the purely Co-terminated interface. We suggest to use such interfaces in thermally operated magnetoresistive random access memory modules, which exploit the magneto-Seebeck effect, to maximize the thermally induced readout voltage.