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, K 1 i j ( r ) , which is suitable for different coupling conditions, and expresses well the coherency between soft and hard grains. The average anisotropy of grain 〈 K i j 〉 has been calculated based on K 1 i j ( r ) and the theory of partial exchange-coupling interaction. It has been found that the average anisotropy of hard or soft grain, 〈 K h h 〉 or 〈 K s s 〉 , 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 K 1 s h ( 0 ) , which denotes the affection degree of hard grain on the anisotropy of soft grain. Compared with other results, it is more reasonable that K 1 s h ( 0 ) ranges from 0.5 K 1 h to 0.7 K 1 h . The variations of anisotropy with D we calculated are consistent with those of coercivities given by other authors when K 1 i j ( 0 ) is fixed in a certain range.