Spin-dependent Seebeck coefficients of Ni_{80}Fe_{20} and Co in nanopillar spin valves

TL;DR

This study experimentally measures the spin-dependent Seebeck coefficients of Ni80Fe20 and Co in nanopillar spin valves, using a specialized device and 3D finite-element modeling to separate heat and charge effects, providing new quantitative insights.

Contribution

It introduces a method combining nanopillar devices and 3D-FEM modeling to accurately determine spin-dependent Seebeck coefficients in ferromagnetic materials.

Findings

Cobalt's spin-dependent Seebeck coefficient is -1.8 μV/K.

Permalloy's spin-dependent Seebeck coefficient is -4.5 μV/K.

The polarization of the Seebeck coefficient is 0.08 for Co and 0.25 for permalloy.

Abstract

We have experimentally determined the spin-dependent Seebeck coefficient of permalloy (Ni_{80}Fe_{20}) and cobalt (Co) using nanopillar spin valve devices. The devices were specifically designed to completely separate heat related effects from charge related effects. A pure heat current through the nanopillar spin valve, a stack of two ferromagnetic layers (F) separated by a non-magnetic layer (N), leads to a thermovoltage proportional to the spin-dependent Seebeck coefficient S_{S}=S_{\uparrow}-S_{\downarrow} of the ferromagnet, where S_{\uparrow} and S_{\downarrow} are the Seebeck coefficient for spin-up and spin-down electrons. By using a three-dimensional finite-element model (3D-FEM) based on spin-dependent thermoelectric theory, whose input material parameters were measured in separate devices, we were able to accurately determine a spin-dependent Seebeck coefficient of -1.8 microvolt/Kelvin and -4.5 microvolt/Kelvin for cobalt and permalloy, respectively corresponding to a Seebeck coefficient polarization P_{S}=S_{S}/S_{F} of 0.08 and 0.25, where S_{F} is the Seebeck coefficient of the ferromagnet. The results are in agreement with earlier theoretical work in Co/Cu multilayers and spin-dependent Seebeck and spin-dependent Peltier measurements in Ni_{80}Fe_{20}/Cu spin valve structures.