Effective Anisotropy in Magnetically Nd2Fe14B/α-Fe Nanocomposite

Considering different contact situations of grains, we effective anisotropies of magnetically soft α-Fe grains, investigate the effects of exchange-coupling interaction on hard Nd2Fe14B grains and NdaFe14B/α-Fe nanocomposite. An expression of effective anisotropy suitable for different degrees of exchange-coupling between grains is presented. The calculation results show that the exchange-coupling interaction increases the average anisotropy of soft grains and decreases that of hard grains. The effective anisotropy of Nd2Fe14B/α-Fe nanocomposite decreases smoothly with decreasing grain size when the grain size is larger than 20 nm while it decreases dramaticaily with further decrease of the grain size. In order to maintain high coercivity in Nd2Fe14B/α-Fe nanoeomposite, the grain size should not be less than 20nm.