  In spintronics, it is important to be able to manipulate magnetization
rapidly and reliably. Several methods can control magnetization, such as by
applying current pulses or magnetic fields. An applied current can reverse
magnetization with nanosecond speed through the spin torque effect. For faster
switching, subpicosecond switching with femtoseconds laser pulse has been
achieved in amorphous rare-earth transition-metal ferrimagnets. In this study,
we employed atomistic simulations to investigate ultrafast switching in a
synthetic antiferromagnet with bilayer amorphous FeGd ferrimagnets. Using a
two-temperature model, we demonstrated ultrafast switching in this synthetic
antiferromagnet without external magnetic fields. Furthermore, we showed that
if we initially stabilize a skyrmion in this heterostructure, the ultrafast
laser can switch the skyrmion state using the same mechanism. Furthermore, this
bilayer design allows the control of each ferrimagnetic layer individually and
opens the possibility for a magnetic tunnel junction.
