  The control of spin current is pivotal for spintronic applications,
especially for spin-orbit torque devices. Spin Hall effect (SHE) is a prevalent
method to generate spin current. However, it is difficult to manipulate its
spin polarization in nonmagnet. Recently, the discovery of spin current in
ferromagnet offers opportunity to realize the manipulation. In the present
work, the spin current in van der Waals ferromagnet Fe3 GeTe2 (FGT) with
varying magnetization is theoretically investigated. It has been observed that
the spin current in FGT presents the nonlinear behavior with respect to
magnetization. The in-plane and out-of-plane spin polarization emerges
simultaneously, and the bilayer FGT can even exhibit arbitrary spin
polarization thanks to the reduced symmetry. More intriguingly, the correlation
between anomalous Hall effect (AHE) and spin anomalous Hall effect (SAHE) has
been interpreted from the aspect of Berry curvature. This work illustrates that
the interplay of symmetry and magnetism can effectively control the magnitude
and spin polarization of the spin current, providing a practical method to
realize exotic spin-orbit torques.
