Subpicosecond magnetization dynamics in TbCo alloys

Since the discovery of all-optical magnetization switching in rare-earth transition-metal alloys the underlying magnetization dynamics of multisublattice magnets has become a hot topic of modern magnetism. We studied the ultrafast magnetization dynamics in TbCo alloys as a function of the alloy composition and the laser fluence using either 800 nm or 400 nm probe pulses. Direct comparison between TbCo samples with different compositions for equal excitation conditions demonstrates that the magnetization dynamics of the Co sublattice strongly depends on the Tb concentration. For Tb32Co68 the magnetization of the sublattices can even transiently be reversed on a subpicosecond time scale.