GRAIN-SIZE DEPENDENCE OF REMANENCE AND COERCIVE FIELD OF ISOTROPIC NANOCRYSTALLINE COMPOSITE PERMANENT-MAGNETS

Micromagnetic calculations using a finite element technique are useful to investigate magnetization processes in nanocrystalline ferromagnet ic materials. In particular numerical calculations reveal the microstr uctural conditions required for high remanence and high coercivity iso tropic permanent magnets. composite materials of Nd2Fe14B and alpha-Fe are excellent candidates for such high performance permanent magnets, The soft magnetic alpha-Fe grains cause a large spontaneous magnetiza tion and the hard magnetic grains induce a large coercive field, provi ded that both phases are strongly exchange coupled. The numerical inve stigations on realistic three-dimensional grain arrangements suggest a n optimal microstructure consisting of small soft magnetic grains (D a pproximate to 10 nm, V-soft approximate to 40%) embedded between hard magnetic grains with a mean grain diameter of about D approximate to 2 0 nm. Additionally, a microstructure with regular shaped grains improv es the magnetic properties.