Ultrafast Photoinduced Softening in a III-V Ferromagnetic Semiconductor for Non-thermal Magneto-Optical Recording

Through time-resolved two-color magneto-optical Kerr spectroscopy we have demonstrated that photogenerated transient carriers decrease the coercivity of ferromagnetic InMnAs at low temperatures. This transient ``softening'' persists only during the carrier lifetime ($\sim$ 2 ps) and returns to its original value as soon as the carriers recombine to disappear. We discuss the origin of this unusual phenomenon in terms of carrier-enhanced ferromagnetic exchange interactions between Mn ions and propose an entirely nonthermal scheme for magnetization reversal.