All-optical four-state magnetization reversal in (Ga,Mn)As ferromagnetic   semiconductors
  Using density matrix equations of motion and a tight-binding band calculation, we predict all-optical switching between four metastable magnetic states of (III,Mn)As ferromagnets. This switching is initiated non-thermally within 100fs, during nonlinear coherent photoexcitation. For a single optical pulse, magnetization reversal is completed after $\sim$100 ps and controlled by the coherent femtosecond photoexcitation. Our predicted switching comes from magnetic nonlinearities triggered by a femtosecond magnetization tilt that is sensitive to un--adiabatic light--induced spin interactions. 
M. D. Kapetanakis, P. C. Lingos, C. Piermarocchi, J. Wang and I. E.   Perakis
physics.optics cond-mat.mtrl-sci