Hysteresis effects in amorphous magnetic alloys containing rare earths

The Monte Carlo technique is used to study the zero-temperature properties of the random magnetic anisotropy model for amorphous rare earth alloys. The system consists of 512 spins on a simple cubic lattice, and periodic boundary conditions are imposed. The model has been studied for both ferromagnetic and antiferromagnetic exchange coupling. In the case of ferromagnetic exchange, the internal energy surface is found to possess an absolute minimum, which corresponds to the "ferromagnetic" state, and numerous local minima, which correspond to "spin glass" states. The hysteresis loops have relatively square shapes, resembling those for rare earth-iron alloys. The coercive field is found to vary roughly linearly with the anisotropy parameter. In the case of antiferromagnetic exchange, the demagnetized state can be of either "antiferromagnetic" character or "spin glass like" character. The hysteresis loops are much smoother and the reduced remanence is always less than 0.5. These results are discussed in the context of experimental data for rare earth-silver alloys.