Revealing the role of orbital magnetism in ultrafast laser-induced   demagnetization in multisublattice metallic magnets by terahertz spectroscopy
  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. 
T. J. Huisman, R. V. Mikhaylovskiy, A. Tsukamoto, Th. Rasing and A. V.   Kimel
cond-mat.mtrl-sci