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, K1ij(r), which is suitable for different coupling conditions, and expresses well the coherency between soft and hard grains. The average anisotropy of grain 〈Kij〉〈Kij〉 has been calculated based on K1ij(r) and the theory of partial exchange-coupling interaction. It has been found that the average anisotropy of hard or soft grain, 〈Khh〉〈Khh〉 or 〈Kss〉〈Kss〉, increases with increasing grain size DD monotonously when hard–hard or soft–soft grains couple. When soft–hard grains touch each other, with increasing DD, the variation of average anisotropy of soft–hard grain 〈K〉〈K〉 depends on the anisotropy at grain interface K1sh(0), which denotes the affection degree of hard grain on the anisotropy of soft grain. Compared with other results, it is more reasonable that K1sh(0) ranges from 0.5K1h to 0.7K1h. The variations of anisotropy with DD we calculated are consistent with those of coercivities given by other authors when K1ij(0) is fixed in a certain range.