Magnetization-Independent Spin Hall Effect in a Ferromagnetic Metal

Exploring the physics of spin transport in ferromagnetic metals (FMs) has been a central challenge in magnetism and spintronics. In a FM, an electric field E generates a spin current flowing along the m×E direction with a spin direction along m, where m denotes the unit vector of the magnetization. The generation of such a spin current is referred to as the spin anomalous Hall effect (SAHE). In the SAHE, the spin direction σ of the spin current can be changed by controlling m because of σ//m. This is contrary to the spin Hall effect (SHE) in nonmagnetic metals (NMs), where σ is geometrically fixed; σ is perpendicular to both E and the flow direction of the spin current. As in the case of the SAHE, it has been commonly assumed that the spin direction of spin currents in FMs is aligned with m because of spin dephasing.

In this research, we demonstrate the isotropic SHE in the epitaxial ferromagnet by measuring the spin orbit torques for the Co/Ti/Fe3Si(001) device. From the ST-FMR measurements, we find that the SHE in the Fe₃Si layer generates spin Hall currents with a spin direction non-collinear with the magnetization. Furthermore, we show that the spin Hall currents in the Fe₃Si layer are unchanged by the change in the direction of the magnetization. This result demonstrates that the intrinsically generated transverse spins are free from dephasing and that the SHE in the ferromagnet is isotropic.