Ultrafast spin demagnetization by nonthermal electrons of TbFe alloy film

An ultrafast spin demagnetization process of an amorphous Tb35Fe65 alloy film has been investigated by means of an all-optical pump-probe technique. Interestingly, steplike demagnetization on a subpicosecond time scale is observed before a much slower change on a time scale of tens of picoseconds. The steplike demagnetization at the subpicosecond scale is explained by the extended three-temperature model considering the interaction between a nonthermal electron and a spin system. The characteristic of subpicosecond demagnetization of TbFe alloy film is expected to be very useful in the manipulation of the spin state in ultrafast regime.