Ultrafast manipulation of magnetic anisotropy in a uniaxial intermetallic heterostructure TbCo2/FeCo

We study experimentally and theoretically the dynamics of spin relaxation motion excited by a femtosecond pulse in the TbCo2/FeCo multilayer structures with different ratios of TbCo2 to FeCo thicknesses r(d) = d(TbCo)(2)/d(FeCo). The main attribute of the structure is in-plane magnetic anisotropy that is artificially induced during sputtering under a DC magnetic field. The optical pump-probe method revealed strongly damped high-frequency oscillations of the dynamical Kerr rotation angle, followed by its slow relaxation to the initial state. Modeling experimental results using the Landau-Lifshitz-Gilbert (LLG) equation showed that the observed entire dynamics is due to destruction and restoration of magnetic anisotropy rather than to demagnetization. For the pumping fluence of 7 mJ cm(-2), the maximal photo-induced disruption of the anisotropy field is about 14% for the sample with r(d) = 1 and decreases when r(d) increases. The anisotropy relaxation is a three-stage process: the ultrafast one occurs within several picoseconds, and the slow one occurs on a nanosecond time scale. The Gilbert damping in the multilayers is found to be one order of magnitude higher than that in the constituent monolayers.

Automated summary

We studied the dynamics of spin relaxation motion excited by a femtosecond pulse in TbCo2/FeCo multilayer structures with different thickness ratios of TbCo2 to FeCo. The main finding of this study is that the observed dynamics is attributed to the destruction and restoration of magnetic anisotropy, rather than demagnetization. Additionally, the Gilbert damping in the multilayers is found to be one order of magnitude higher than that in the constituent monolayers.