Effects of phase distribution and grain size on the effective anisotropy and coercivity of nanocomposite Nd2Fe14B∕α-Fe magnets

Abstract

The effects of phase distribution and grain size on the effective anisotropy and coercivity of the exchange-coupled nanocomposite permanent materials have been investigated in this paper. The effective anisotropy of nanocomposite permanent materials is supposed to be equal to the statistical average value of the anisotropy of magnetically soft and hard grains. The dependence of coercivity on grain sizes is mainly determined by the effective anisotropy of the grains. The calculated results show that, when the grain sizes of the soft and hard phases are identical and the volume fraction of the hard phase is given, the coercivity decreases with the reduction of the grain size. For the given size of the soft grains and the volume fraction of the hard phase, the coercivity shows a peak value as a function of the hard-grain size. The experimental enhancement of the coercivity with reducing grain size is attributed not to only the exchange-coupling interactions but also to the phase distribution.