  The anomalous Hall effect is mainly used to probe the magnetization
orientation in ferromagnetic materials. A less explored aspect is the torque
acting back on magnetization, an effect that can be important at high currents.
The spin-orbit coupling of the conduction electrons causes spin-up and
spin-down electrons to scatter to opposite sides when a charge current flows in
the sample. This is equivalent to a spin current with orientation and flow
perpendicular to the driving charge current, leading to a non-equilibrium spin
accumulation that exerts a torque on the bulk magnetization through the s-d
exchange interaction. The symmetry of this toque is that of an uniaxial
anisotropy along the driving current. The large screening currents generated
with laser pulses in all-optical magnetic switching experiments make for
practical uses of this torque.
