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

Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan(Dated: February 6, 2008)Through time-resolved two-color magneto-optical Kerr spectroscopy we have demonstrated thatphotogenerated transient carriers decrease the coercivity of ferromagnetic InMnAs at low tempera-tures. This transient “softening” persists only during the carrier lifetime (∼ 2 ps) and returns to itsoriginal value as soon as the carriers recombine to disappear. We discuss the origin of this unusualphenomenon in terms of carrier-enhanced ferromagnetic exchange interactions between Mn ions andpropose an entirely nonthermal scheme for magnetization reversal.