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

Measurements of the spin heat accumulation at the ferromagnetic/non-magnetic interface in nanopillar spin valves show that spin-up and spin-down electrons have different temperatures. This observation is important for the design of magnetic thermal switches and the study of inelastic spin scattering. Since the discovery of the giant magnetoresistance effect 1 , 2 the intrinsic angular momentum of the electron has opened up new spin-based device concepts. Our present understanding of the coupled transport of charge, spin and heat relies on the two-channel model for spin-up and spin-down electrons having equal temperatures. Here we report the observation of different (effective) temperatures for the spin-up and spin-down electrons in a nanopillar spin valve subject to a heat current. By three-dimensional finite element modelling 3 of our devices for varying thickness of the non-magnetic layer, spin heat accumulations (the difference of the spin temperatures) 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 nanopillar. This technique uniquely allows the study of inelastic spin scattering at low energies and elevated temperatures, which is not possible by spectroscopic methods.