Thermal gradient driven enhancement of pure spin current at room temperature in nonlocal spin transport devices

We show that the junction design in the laterally configured ferromagnetic/nonmagnetic (FM/NM) hybrid structure significantly affects the spin transport under high-bias current. The thermal conductivity mismatch between FM and NM and the inhomogeneous current distribution at the interface produce a reversed temperature gradient, which drastically reduces the thermal spin injection efficiency. The homogeneity in the temperature gradient at the interface is a crucial factor in determining the efficiency of the thermal spin current generation. The experimental results show excellent agreement with the theoretical model [Y. Takezoe et al., Phys. Rev. B 82, 094451 (2010)] that the spin relaxation is proportional to the second spatial derivative of the temperature.