  The interaction of polarized light with a spin in the presence of dissipation
is shown to be equivalent to a spin transfer process that can cause switching.
In plasmas, the spin transfer is dominated by a spin-spin exchange term while
at lower energy densities it is dominated by an optical Barnett-like effect.
This latter effect is used in conjunction with optical phonons to predict
femtosecond magnetization reversal believed to be recently measured in GdCoFe
thin films. Conventional approaches based on the Bloch and the Landau-Lifshitz
equations do not reproduce this ultrafast switching.
