Comparison between thermal and current driven spin-transfer torque in nanopillar metallic spin valves

Abstract

We investigate the relation between thermal spin-transfer torque (TSTT) and the spin-dependent Seebeck effect (SDSE), which produces a spin current when a temperature gradient is applied across a metallic ferromagnet, in nanopillar metallic spin valves. Comparing its angular dependence (aSDSE) with the angle dependent magnetoresistance (aMR) measurements on the same device, we are able to verify that a small spin heat accumulation builds up in our devices. From the SDSE measurement and the observed current driven STT switching current of 0.8 mA in our spin valve devices, it was estimated that a temperature difference of 230 K is needed to produce an equal amount of TSTT. Experiments specifically focused on investigating TSTT show a response that is dominated by overall heating of the magnetic layer. Comparing it to the current driven STT experiments we estimate that only ~10% of the response is due to TSTT. This leads us to conclude that switching dominated by TSTT requires a direct coupling to a perfect heat sink to minimize the effect of overall heating. Nevertheless the combined effect of heating, STT and TSTT could prove useful for inducing magnetization switching when further investigated and optimized.