  Simultaneous detection of THz emission and transient magneto-optical response
is employed to study ultrafast laser-induced magnetization dynamics in
multisublattice magnets NdFeCo and GdFeCo amorphous alloys with in-plane
magnetic anisotropy. A satisfactory quantitative agreement between the dynamics
revealed with the help of these two techniques is obtained for GdFeCo. For
NdFeCo the THz emission reveals faster dynamics than the magneto-optical
response. This indicates that in addition to spin dynamics of Fe ultrafast
laser excitation triggers faster magnetization dynamics of Nd.
