Abstract:
Pure spin current has the advantage of carrying the maximum angular momentum with the minimum charge carriers. More interestingly, pure spin current can be carried by magnons in magnetic insulators where no charge carriers are required at all. In order to generate a pure spin current, commonly used methods include the spin Hall effect (SHE) in a nonmagnetic metal or the spin Seebeck effect (SSE) in a ferromagnetic insulator via electrical or thermal means, respectively. Conventional SHE converts a charge current into a transverse spin current with the spin index pointing in the third direction. Conventional SSE excites a spin current in the longitudinal direction under the application of the out-of-plane heat current. In addition to the conventional spin current generation, in this talk, I will discuss two unconventional effects in generating the spin current electrically and thermally. They are the magnetization dependent spin Hall effect (MDSHE) in a ferromagnetic metal and the vector spin Seebeck effect (VSSE) in a non-collinear antiferromagnetic insulator. In the MDSHE, with a charge current flow in the ferromagnetic metal, the generated spin current has a spin index that does not follow a strict orthogonal relation as in conventional SHE; in contrast, it can be arbitrarily controlled by the magnetization direction of the magnetic metal. In the VSSE, under a heat current, we observe not only a longitudinal but also a transverse spin current generation, which is caused by the vector magnetization in the non-collinear spin structure in the antiferromagnetic insulator. Our study opens up new aspects in studying the pure spin current generation and conversion in magnetic materials.