Determination of spin-dependent Seebeck coefficients of CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars

TL;DR

This study measures the spin-dependent Seebeck coefficients in CoFeB/MgO/CoFeB magnetic tunnel junctions, revealing large thermoelectric effects and their dependence on magnetic states, advancing understanding of spin caloritronics.

Contribution

It provides the first detailed measurement of spin-dependent Seebeck coefficients in CoFeB/MgO/CoFeB MTJs, demonstrating significant thermoelectric effects linked to magnetic configurations.

Findings

Large spin-dependent Seebeck coefficients (~240 μV/K) were observed.

Thermo power voltage scales linearly with heating power.

Tunneling magneto thermopower up to 90% was achieved.

Abstract

We investigate the spin-dependent Seebeck coefficient and the tunneling magneto thermopower of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. Thermal gradients are generated by an electric heater on top of the nanopillars. The thermo power voltage across the MTJ is found to scale linearly with the heating power and reveals similar field dependence as the tunnel magnetoresistance. The amplitude of the thermal gradient is derived from calibration measurements in combination with finite element simulations of the heat flux. Based on this, large spin-dependent Seebeck coefficients of the order of (240 \pm 110) \muV/K are derived. From additional measurements on MTJs after dielectric breakdown, a tunneling magneto thermopower up to 90% can be derived for 1.5 nm MgO based MTJ nanopillars.