  Thermally-assisted ultra-fast magnetization reversal in a DC magnetic field
for magnetic multilayer thin films with perpendicular anisotropy has been
investigated in the time domain using femtosecond laser heating. The experiment
is set-up as an optically pumped stroboscopic Time Resolved Magneto-Optical
Kerr Effect magnetometer. It is observed that a modest laser fluence of about
0.3 mJ/square-cm induces switching of the magnetization in an applied field
much less than the DC coercivity (0.8 T) on the sub-nanosecond time-scale. This
switching was thermally-assisted by the energy from the femtosecond pump-pulse.
The experimental results are compared with a model based on the Landau
Lifschitz Bloch equation. The comparison supports a description of the reversal
process as an ultra-fast demagnetization and partial recovery followed by
slower thermally activated switching due to the spin system remaining at an
elevated temperature after the heating pulse.
