Role of exchange parameters for ultrafast thermally induced magnetization switching in ferrimagnets

The ultrafast deterministic thermally induced magnetization switching (TIMS) under the excitation by a one-shot femtosecond laser pulse has been widely achieved in disordered ferrimagnetic alloys such as GdFeCo. Among multiple factors influencing the occurrence of this phenomenon, the role of the exchange parameters is poorly understood. Here, using atomistic spin simulations based on the spin Hamiltonian parameterized through ab initio calculations for ordered stoichiometric ${\text{GdFe}}_{2}$ and ${\text{TbFe}}_{2}$ Laves phases $C15$, we investigate the conditions for the occurrence of deterministic TIMS. Our simulations show that both inter- and intrasublattice exchange interactions are too strong in ordered alloys and the switching is not produced for any excitation. By varying the exchange parameters, we find their regions for which the deterministic TIMS takes place in some interval of laser fluence. Consequently, neither weakly nor strongly antiferromagnetically coupled materials would switch. This explains the success of disordered alloys to produce this phenomenon since the average strength of the exchange interactions is mediated by the rare-earth-metal concentration in this case. Our simulations also show that in the ordered lattice case only materials possessing the magnetization compensation point are switched by this mechanism.