Effects of intergranular phase on the exchange-coupling interaction and effective anisotropy of nanocrystalline Nd2Fe14B materials

The effects of intergranular phase with different thickness, dd, on the exchange-coupling interaction and effective anisotropy in nanocrystalline Nd2Fe14B material have been investigated by adopting a cube model of grain and putting forward two assumed expressions of anisotropy, K1lay (rr), in the coupled part of the grain interface. The results showed that both the average anisotropy of the grain, 〈K〉〈K〉, and the effective anisotropy of the material, Keff, increase with increasing grain size, DD. 〈K〉〈K〉 calculated based on the two expressions increases with increasing dd. However, the variations of Keff with dd based on the two expressions are different. Based on the first expression, K1′lay(r), Keff increases firstly and decreases subsequently with increasing dd, and shows maximum value at certain dd. Based on the second expression, K1″lay(r), Keff decreases monotonously with increasing dd. The variation tendency of effective anisotropy is basically similar to that of other authors’ calculated and experimental coercivity. The existence of intergranular phase with suitable thickness may result in an increase of effective anisotropy and coercivity.