The Role of the Magnetic Interactions

The magnetization reversal is a collective process that involves the interaction of magnetization in different grains. The micromagnetic simulations allow one to predict the influence of the interactions by slowly varying their strength, which is not accessible by any experimental technique. They even allow separating the influence of different contributions, such as to take into account separately magneto-static or exchange ones [111]. The presence of interactions, together with the microstructure, drastically influences the remanence and coercive field. At T = 0 K for a system of noninteracting grains with easy axes randomly oriented, the Stoner-Wolfarth theory [131] shows that the hysteresis loop has a reduced remanence Mr/Ms = 0.5. In general, the values Mr/Ms less than 0.5 have been reported, which was attributed to interaction effects [132, 133].

It should be noted that the exchange energy contribution evaluation experiences significant arbitrarity grades for

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