抄録
This paper summarizes the recent results in laser-induced magnetization dynamics, in particular, the direct nonthermal opto-magnetic excitation of spin systems in GdFeCo metallic film. Using an all-optical pump and probe technique, we have investigated the temperature dependence of the ultrafast magnetic response in a perpendicularly magnetized ferrimagnetic amorphous GdFeCo thin film. This ferromagnetic film shows large temperature dependence of magnetic resonance frequency. When the temperature of the sample approaches the angular momentum compensation point, both frequency and the Gilbert damping parameter of the magnetization precession increase significantly. By turning the sample into a multidomain state and thereby suppressing the observation of the heating effect of light, we succeeded to measure an ultrafast nonthermal excitation of spin waves with a phase that depends on the angular momentum of the photons. Moreover, the magnetization could be reversed in a reproducible manner by single 40 fs circularly polarized laser pulses, without an external magnetic field. The direction of this opto-magnetic switching is determined only by the helicity of light pulse. These findings open new insights into the understanding of ultrafast magnetic excitation and may provide new prospects for applications of ultrafast opto-magnetic phenomena in magnetic storage and spintronic technology.
