Ultrafast hot-electron induced quenching of Tb 4 f magnetic order

We have investigated ultrafast quenching of the Tb 4f magnetic order in Co 74 Tb 26 alloys, induced by femtosecond hot-electron pulses. The hot-electron pulses were produced in specific nonmagnetic capping layers by infrared femtosecond laser pulses. Our experimental results show that subpicosecond dynamics of Tb 4f magnetic moments can be induced by nonthermal and thermal hot-electron. We further demonstrate that the demagnetization efficiencies of nonthermal and thermal hot-electron are similar. However, the characteristic demagnetization times show values of 0.35 ps for nonthermal hot-electron excitations and 1.2 ps for thermal hot-electron excitations. We explain this temporal elongation by the propagation time of thermal hot-electron through the 15-nm-thick CoTb film.