NdFeB纳米复合永磁材料的交换耦合相互作用和有效各向异性

以Nd₂Fe₁₄B/αFe为例，采用立方体晶粒结构模型，研究了纳米复合永磁材料中不同磁性晶粒间的交换耦合相互作用和有效各向异性.纳米复合永磁材料的有效各向异性Keff等于软、硬磁性相各向异性的统计平均值，每个晶粒的各向异性由晶粒表面交换耦合部分和晶粒内部未交换耦合部分的各向异性共同确定.计算结果表明，软、硬磁性相晶粒尺寸分布显著地影响有效各向异性Keff的值.当软、硬磁性晶粒尺寸D相同时，Keff随晶粒尺寸和硬磁性相体积分数的降低而减小, 当D<20nm 时，K 关键词： 纳米复合永磁材料 交换耦合相互作用 有效各向异性 晶粒尺寸

Exchange-coupling interaction and effective anisotropy of NdFeB nanocomposite permanent magnetic materials

Taking Nd₂Fe₁₄B/αFe as a typical sample and adopting the cubic grain model，we investigated the exchange-coupling interaction between different magnetic grains and the effective anisotropy of nanocomposite permanent materials in this paper . The effective anisotropy of nanocomposite permanent materials, Keff, is equal to statistical mean values of the effective anisotropy of magnetically soft and hard grains. Every grain's anisotropy is determined by the anisotropy constants of the coupled part at grain boundaries and the internal uncoupled part. The ca lculated results reveal that the distributions of soft and hard grain sizes influence th e effective anisotropy. When the sizes of magnetically soft and hard grains are identical, the effective anisotropy decreases with the reduction of grain size a nd hard phase component, and decreases rapidly while the grain size is less than 20nm. When the soft-grain sizes are of some definite values, Keff shows a maximum value with the variation of the hard-grain size. The hard-grain s izes corre spo nding to the maximum of Keffdecrease with the increase of soft phase components and the reduction of soft grain sizes. The grain size dependence ofKeffis bas ically similar to that of coercivity. The decrement of coercivity for nanoco m posite permanent materials is mainly due to the reduction of effective anisotrop y.