Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation

Time-resolved magneto-optical Kerr spectroscopy of ferromagnetic InMnAs reveals two distinct demagnetization processes—fast ($<1\mathrm{ps}$) and slow ($\sim 100\mathrm{ps}$). 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 ($>10\mathrm{mJ}/{\mathrm{cm}}^2$); the saturation value indicates a complete quenching of ferromagnetism on a subpicosecond time scale. We attribute this fast dynamics to spin heating through $p\mathrm{\text{−}}d$ exchange interaction between photocarriers and Mn ions, while the $\sim 100\mathrm{ps}$ component is interpreted as spin-lattice relaxation.

Figure 1

(a) The first 3 ps of demagnetization dynamics in $\mathrm{InMnAs}/\mathrm{GaSb}$. Also shown is the cross correlation between the pump and probe pulses. (b) Demagnetization dynamics covering the entire time range of the experiment (up to $\sim 1\mathrm{ns}$). There is a slow demagnetization process, which follows the fast component shown in (a) and completes only after $\sim 100\mathrm{ps}$.

Figure 2

(a) Steady-state MOKE angle versus magnetic field, taken with a 775 nm laser diode. (b) Magnetic field dependence of ultrafast demagnetization dynamics. The sign of the MOKE angle change depends on the direction of the applied magnetic field in a symmetric manner, as expected. (c) Comparison between MOKE (${\theta }_K$) and MCD (${\eta }_K$) dynamics, showing no time lag between them.

Figure 3

Normalized photoinduced MOKE angle change (a) versus time for different pump fluences and (b) versus pump fluence for different time delays. At high fluences, the signal saturates to $\sim 1$, suggesting a complete quenching of ferromagnetic order.

Figure 4

Photoinduced MOKE angle change (a) versus time for different temperatures and (b) versus temperature for different time delays. The photoinduced change is absent above the Curie temperature ($\sim 60\mathrm{K}$).