Non Local Spin Detection in Ferromagnet/Superconductor/Ferromagnet Spin-Valve Device with Double-Tunnel Junctions

摘要

The nonequilibrium spin accumulation in a nonmagnetic material caused by spin injection from ferromagnets can be detected as a voltage signal by the non local measurement technique. We applied this technique to a Ni_(81)Fe_(19)/Al/Ni_(81)Fe_(19) spin-valve device with double-tunnel junctions to explore the effect of spin injection into the superconducting state of aluminum. The non local signal as a function of the external magnetic field and the injection current was found to behave very differently between the normal state at 10 K and the superconducting state at 0.5 K. The observed spin signal, up to 4 mΩ at 0.5 K, was 8 times larger than the signal at 10 K. We also found that the non local spin signal in the superconducting state drastically depended on the injection current, which was not the case for the normal state.