Composition and temperature-dependent magnetization dynamics in ferrimagnetic TbFeCo

Abstract

The temperature-dependent magnetization dynamics in ferrimagnetic TbFeCo alloys with various compositions of Tb is investigated by the pump-probe time-resolved magneto-optical Kerr effect (TR-MOKE) in different geometries. It is shown that, for the case when a magnetic field is applied noncollinearly to the easy axis at room temperature, the decrease of the MOKE signal occurring at several tens of picoseconds (ps) after a rapid demagnetization within a few hundred femtoseconds (fs) is in fact caused by a highly damped precessional motion with precession lifetime shorter than the precession period. This is demonstrated by reducing the Tb content to 6% in atomic ratio and measuring TR-MOKE at elevated temperatures. This has the dual effect of reducing the damping constant allowing the observation of more precession cycles and of weakening the exchange interaction between Tb and FeCo, making the precession oscillations more pronounced. The results give important insight into the ultrafast spin dynamics of rare-earth-doped transition-metal alloys, and the remarkable impact of Tb on the damping in such alloy systems.