First- and second-harmonic detection of spin accumulation in a multiterminal lateral spin valve under high-bias ac current

We have investigated the transport properties of electrically and thermally excited spin currents in a lateral spin valve consisting of a spin injector and detector with a middle ferromagnetic wire by detecting the first- and second-harmonic voltages. The first-harmonic spin signal was significantly suppressed by the middle ferromagnetic wire because of the spin absorption effect. On the other hand, in the second-harmonic signal, a small signal related to the middle ferromagnetic wire was observed in addition to a conventional spin signal with a reduced magnitude. This indicates that the additional ferromagnetic wire acts not only as the spin absorber but also as another spin injector under thermal spin injection, because the heat current caused by direct spin injection propagates to the middle ferromagnetic wire and creates another temperature gradient. By using this effect, we show that the magnetization direction of a ferromagnetic nanodot embedded in a nonmagnetic Cu wire becomes measurable.