Spin heat accumulation and spin-dependent temperatures in nanopillar spin valves

TL;DR

This paper reports the experimental observation of different spin-up and spin-down electron temperatures in nanopillar spin valves under heat current, revealing spin heat accumulation and its weak relaxation at room temperature and 77 K.

Contribution

It demonstrates the first direct detection of spin-dependent electron temperatures in a nanopillar spin valve, advancing understanding of spin caloritronics and inelastic spin scattering.

Findings

Spin heat accumulation of 120 mK at room temperature

Spin heat accumulation of 350 mK at 77 K

Weak relaxation of spin heat inelasticity at room temperature

Abstract

Since the discovery of the giant magnetoresistance (GMR) effect the use of the intrinsic angular momentum of the electrons has opened up new spin based device concepts. The two channel model of spin-up and spin-down electrons with spin-dependent conductivities very well describes spin and charge transport in such devices. In studies of the interaction between heat and spin transport, or spin caloritronics, until recently it was assumed that both spin species are always at the same temperature. Here we report the observation of different temperatures for the spin up (T_\uparrow) and spin down (T_\downarrow) electrons in a nanopillar spin valve subject to a heat current. The weak relaxation, especially at room temperature, of the spin heat accumulation (T_s = T_\uparrow-T_\downarrow) is essential for its detection in our devices. Using 3D finite element modeling spin heat accumulation (SHA) values of 120 mK and 350 mK are extracted at room temperature and 77 K, respectively, which is of the order of 10% of the total temperature bias over the pillar. This technique uniquely allows the study of inelastic spin scattering at low energies and elevated temperatures, which is not possible by spectroscopic methods.