Ultrafast magnetization dynamics: a Review

Electron theory of fast and ultrafast dissipative magnetization dynamics.
M Fähnle and C Illg
J. Phys. CM 23, 493201 (2011)

(a) A sketch of the equilibrium Fermi surface S for time t-dt and time t. In a strict equilibrium situation the yellow
states are occupied only at time t-dt, the red are occupied only at time t, whereas the blue states are occupied at both times. Panel (b) shows a sketch of the equilibrium band structure.