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 that the spin relaxation is proportional to the second spatial derivative of the temperature.