Controlling laser-induced magnetization reversal dynamics in a rare-earth iron garnet across the magnetization compensation point

摘要

In this work we explore the ultrafast magnetization dynamics induced by femtosecond laser pulses in a doped film of gadolinium iron garnet over a broad temperature range including the magnetization compensation point T_m. By exciting the phonon-assisted ~6S → ~4G and ~6S → ~4P electronic d-d transitions simultaneously by one- and two-photon absorption processes, we find out that the transfer of heat energy from the lattice to the spin has, at a temperature slightly below T_M. a large influence on the magnetization dynamics. In particular, we show that the speed and the amplitude of the magnetization dynamics can be strongly increased when increasing either the external magnetic field or the laser energy density. The obtained results are explained by a magnetization reversal process across T_M. Furthermore, we find that the dynamics has unusual characteristics which can be understood by considering the weak spin-phonon coupling in magnetic garnets. These results open new perspectives for controlling the magnetic state of magnetic dielectrics using an ultrashort optically induced heat pulse.