Effect of Grain Size on the Coercivity of Sintered NdFeB Magnets
Sintered NdFeB magnets typically exhibit grain size above 2 micrometers, a value above the single domain particle size (~0.3 micrometers). It is discussed how to obtain relationships between grain size and coercivity with energy balance models, considering formation and annihilation of domain walls as a dissipative process. In the case of nanocrystaline magnets, the Stoner-Wohlfarth model is very suitable. For larger grain sizes, the contribution of the magnetostatic energy of each grain has to be considered. From the concept of meta-stability of domains and domain walls structure, a relation between coercive field and grain size can be estimated.
Lucio Salgado and Francisco Ambrozio Filho
M. F. de Campos "Effect of Grain Size on the Coercivity of Sintered NdFeB Magnets", Materials Science Forum, Vols. 660-661, pp. 284-289, 2010