Fig. 1: Schematic of the microscopic mechanism of manipulation of magnetism by a spin current.

a, The electron spins transmitted into the FM contain both transverse and longitudinal components with respect to M. Owing to exchange coupling, the transverse component dephases and is absorbed by M, which gives rise to the damping-like (DL) SOT and is responsible for changing the direction of M. The longitudinal component of the spin current is on average aligned with M, leading to additional filling of the majority band when M is oriented along the +z direction, and an enhancement of the magnitude M as well as an increase in magnetic anisotropies are expected because of the enhanced exchange splitting of the majority and minority spin energy bands. b, When M is aligned along the –z direction, the spin-polarized electron enters the minority band, which can lead to a decrease in M as well as a decrease in the magnetic anisotropies because of the reduction in the exchange splitting of the majority and minority spin energy bands. c,d, The same as a and b but the polarization of the spin current is reversed, which is expected to reduce M for M ∥ +z (c) and enhance M for M ∥ −z (d).