Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation

Time-resolved magneto-optical Kerr spectroscopy of ferromagnetic InMnAs reveals two distinct {\em demagnetization} processes -- fast ($<1$ ps) and slow ($\sim$100 ps). Both components diminish with increasing temperature and are absent above the Curie temperature. The fast component rapidly grows with pump power and saturates at high fluences ($>10$ mJ/cm$^2$); the saturation value indicates a {\em complete quenching} of ferromagnetism on a sub-picosecond time scale. We attribute this fast dynamics to spin heating through $p$-$d$ exchange interaction between photo-carriers and Mn ions while the $\sim$100 ps component is interpreted as spin-lattice relaxation.