Effect of exchange-coupling interaction on anisotropy of grain in nanoscaled magnets

The effect of inter-grain exchange-coupling interaction on the anisotropy of grain in nanoscaled magnets has been investigated by putting forward an expression of anisotropy at grain boundary, , which is suitable for different coupling conditions, and expresses well the coherency between soft and hard grains. The average anisotropy of grain 〈K^ij〉 has been calculated based on and the theory of partial exchange-coupling interaction. It has been found that the average anisotropy of hard or soft grain, 〈K^hh〉 or 〈K^ss〉, increases with increasing grain size D monotonously when hard-hard or soft-soft grains couple. When soft-hard grains touch each other, with increasing D, the variation of average anisotropy of soft-hard grain 〈K〉 depends on the anisotropy at grain interface , which denotes the affection degree of hard grain on the anisotropy of soft grain. Compared with other results, it is more reasonable that ranges from to . The variations of anisotropy with D we calculated are consistent with those of coercivities given by other authors when is fixed in a certain range.