Ultrafast dynamics of the magneto-optical Kerr effect in multilayer TbCo/FeCo structures under the influence of femtosecond optical excitation

Dynamics of the magneto-optical Kerr effect in a multilayer TbCo2 / FeCo metal structure consisting of alternating layers 1.5 nm thick was studied in this work. The relaxation process was considered over a time interval of up to 170 ps using the femtosecond pump-probe spectroscopy. The experiment was carried out in 2 geometries, when the external field was along the “easy” axis and along the “heavy” axis. The maximum value of the applied magnetic field along the «easy axis» was 4.5 kOe, and along the «heavy» axis 5 kOe. Based on the approximation of the dynamics of the Kerr effect, the dependences of the oscillation frequency, amplitude and decay time are obtained. It is shown that in the geometry of the “heavy axis”, in contrast to the geometry of the “easy axis”, the amplitude of the oscillations is several times larger, and the decay of the precession is several times slower. The dependence of the amplitude of oscillations in the “heavy axis” geometry has a maximum at an external field of about 2 kOe, the value of which is close to the saturation field along this axis.