Thermally assisted ultrafast magnetization reversal in a dc magnetic field in magnetic multilayer thin films with perpendicular anisotropy has been investigated in the time domain using femtosecond laser heating. The experiment is set up as a stroboscopic optical time resolved magneto-optical Kerr effect magnetometer. It is observed that a modest laser fluence of about $0.3\text{mJ}/{\text{cm}}^2$ induces switching of the magnetization in an applied field much less than the dc coercivity (0.8 T) on the subnanosecond 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-Lifshitz-Bloch equation. The comparison supports a description of the reversal process as an ultrafast demagnetization and partial recovery followed by slower thermally activated switching due to the spin system remaining at an elevated temperature after the heating pulse.

• Received 1 July 2009

DOI:https://doi.org/10.1103/PhysRevB.81.174428