Thermal conductivity of thin insulating films determined by tunnel magneto-Seebeck effect measurements and finite-element modeling

TL;DR

This paper introduces a novel method combining tunnel magneto-Seebeck effect measurements with finite-element modeling to accurately determine the thermal conductivity of ultra-thin insulating films, overcoming experimental challenges.

Contribution

The study presents a new approach that uses TMS and FEM to measure thermal conductivity of thin insulating films, providing results consistent with theoretical predictions.

Findings

Thermal conductivity of MAO is 0.7 W/(K·m).

Thermal conductivity of MgO is 5.8 W/(K·m).

Method effectively isolates TMS without parasitic effects.

Abstract

In general, it is difficult to access the thermal conductivity of thin insulating films experimentally just by electrical means. Here, we present a new approach utilizing the tunnel magneto-Seebeck effect (TMS) in combination with finite-element modeling (FEM). We detect the laser-induced TMS and the absolute thermovoltage of laser-heated magnetic tunnel junctions with 2.6 nm thin barriers of MgAl$_2$O$_4$ (MAO) and MgO, respectively. A second measurement of the absolute thermovoltage after a dielectric breakdown of the barrier grants insight into the remaining thermovoltage of the stack. Thus, the pure TMS without any parasitic Nernst contributions from the leads can be identified. In combination with FEM via COMSOL, we are able to extract values for the thermal conductivity of MAO ($0.7$ W/(K$\cdot$m)) and MgO ($5.8$ W/(K$\cdot$m)), which are in very good agreement with theoretical predictions. Our method provides a new promising way to extract the experimentally challenging parameter of the thermal conductivity of thin insulating films.