Chapter Three - Charge, Spin, and Heat Transport in the Proximity of Metal/Ferromagnet Interface

Abstract

The spin Seebeck effect (SSE) is one of the few routes for exploiting the spin degree of electronic transport. The observation of SSE has been reported using transverse and longitudinal geometries with in-plane (∇xT) and out-of-plane temperature (∇zT) gradient, respectively. However, it is hard to create purely in-plane temperature gradient for thin magnetic films on thick substrates. The transverse geometry where temperature gradient is applied along in-plane direction is always accompanied by an unintended out-of-plane temperature gradient due to substrates, which gives rise to the anomalous Nernst effect (ANE). The voltages of transverse SSE with ∇xT and ANE with ∇zT have the same field dependence and angular symmetry and thus are entangled. In the longitudinal SSE applicable for ferromagnetic insulator (e.g., yttrium iron garnet, YIG), the temperature gradient is exclusively out of plane. However, one encounters a different issue of magnetic proximity effects (MPEs) when the spin current detector, Pt, is in contact with YIG where unusual transport phenomena, including magnetoresistance and anomalous Hall effects, exist. These complications present difficulties for the unequivocal establishment of SSE in Pt/YIG. Very recently, the intrinsic SSE using the longitudinal geometry in Au/YIG was reported without appreciable MPE.