The effect of random coercivity on domain growth processes in rare earth–transition metal alloys (abstract)

Abstract

In the present investigation, we show that local fluctuations of the magnetic properties in amorphous alloys, specifically the fluctuating anisotropy, can cause irregularity in the domain shape which has been attributed to causing writing noise.1 We propose a model for coercivity based on the pinning of domain walls by the randomly fluctuating anisotropy constant. This model is believed to be particularly suitable for materials containing non-S-state rare-earth ions like terbium, because the 4f electrons of these ions, through the spin-orbit coupling, interact strongly with the random local electrostatic fields. A computer model developed to simulate dynamic domain wall motion2 is used with a new coercive force model to predict the domain growth process. The effects of the random coercivity on the shape of the written domain were studied for two different processes: (a) thermomagnetic writing by a laser beam and (b) wall motion by thermal activation at a constant temperature. It is shown that domain shape distortion becomes more pronounced as the percentage of the random anisotropy relative to that of the constant anisotropy is increased, particularly in the case of thermal activation.<ks>