Thermal spin injection and interface insensitivity in permalloy/aluminum metallic non-local spin valves

TL;DR

This study investigates thermal and electrical spin injection in nanoscale metallic non-local spin valves, revealing that thermal spin injection is less sensitive to interface effects and could be advantageous for sensor and spin current applications.

Contribution

It provides the first detailed analysis of thermal spin injection limits and interface insensitivity in permalloy/aluminum spin valves, highlighting potential advantages over electrical methods.

Findings

Thermal spin injection is less affected by interface quality.

The spin-dependent Seebeck coefficient is estimated between -0.5 and -1.3 μV/K.

Thermal spin injection signals are comparable to electrical ones despite smaller electrical signals.

Abstract

We present measurements of thermal and electrical spin injection in nanoscale metallic non-local spin valve (NLSV) structures. Informed by measurements of the Seebeck coefficient and thermal conductivity of representative films made using a micromachined Si-N thermal isolation platform, we use simple analytical and finite element thermal models to determine limits on the thermal gradient driving thermal spin injection and calculate the spin dependent Seebeck coefficient to be $-0.5\ \mu\mathrm{V}/\mathrm{K}< S_{s}<-1.3\ \mu\mathrm{V}/\mathrm{K}$. This is comparable in terms of the fraction of the absolute Seebeck coefficient to previous results, despite dramatically smaller electrical spin injection signals. Since the small electrical spin signals are likely caused by interfacial effects, we conclude that thermal spin injection is less sensitive to the FM/NM interface, and possibly benefits from a layer of oxidized ferromagnet, which further stimulates interest in thermal spin injection for applications in sensors and pure spin current sources.