交换耦合作用对纳米复合永磁材料有效各向异性的影响

Effect of exchange-coupling interaction on the effective anisotropy in nanocomposite magnetic material

以Nd_2Fe_(14)B/α-Fe纳米复合永磁材料为例,采用立方体晶粒结构模型,研究了单个晶粒中存在不同耦合状态时,有效各向异性随晶粒尺寸的变化关系.采用边界值不为零的变化函数研究了耦合部分各向异性随耦合长度的变化.计算结果表明:当两相耦合时,软磁晶粒的有效各向异性随晶粒尺寸的增加而减小,硬磁晶粒的有效各向异性随晶粒尺寸的增加而增加.对于存在软、硬两相的复合磁体,为保证较高的有效各向异性值,晶粒尺寸应保持在25nm左右.

Based on a cubic grain model, the variation of the effective anisotropy in Nd2Fe14B/α-Fe nanocrystalline permanent magnet at different coupling state was investigated. An expression of ani sotropy at grain boundary suitable for different coupling conditions was given. The results showed that the effective anisotropy of soft grains increased with the reduction of grain size and the increase of coupled part when soft hard coupling existed, but the effective anisotropy of hard grain had an opposite result. From the curve of effective anisotropy of nanocrystalline magnet, the grain size should be about 25 nm in order to obtain higher effective anisotropy between magnetically soft and hard grains.