Magnetic properties of amorphous rare earth-transition metal alloys for erasable optical storage

A mean-field modelfor amorphous rare earth-transition metal (RE-TM) alloys is developed and compared with available experimental data on GdCo-, GdFe-and TbFe-based alloys. The model assumes the existence of two iron subnetworks, one with ferromagnetic and the other with antiferromagnetic exchange coupling. The fraction of iron ions in each subnetwork and the magnetic moment of the TM ion are the only adjustable parameters of the model. Good agreement is obtained in all cases between the model calculations and the experimental data. Preliminary measurements of the magneto-optic Kerr effect on TbFe samples are also reported and the results are compared with the mean-field model predictions. A phenomenological model for the anisotropy energy density constant (Ku) is proposed and the results are tied to the mean-field model for calculations of domain wall properties. Finally, the magnetization reversal process and the nature of coercivity in thin films of TbFe are investigated, and the nucleation, growth, and stability of domains are discussed in terms of simple phenomenological models.