NUCLEATION AS COERCIVITY MECHANISM IN NDFEB MAGNETS

In the first part of this article, the SW-CLC (Stoner-Wohlfarth with CLC modification) model is discussed for nanocrystalline magnets, as melt-spun exchange coupled NdFeB. In the second part, the effect of grain size of coercivity for large grain size, above the single domain particle size, is addressed. The Kondorsky law observed for large grain size only can be due to domain wall displacement phenomena, where there is nucleus expansion. There are two main situations, one for nanocrystalline grain size, where the SW-CLC model is obeyed, and other for large grain size, where the coercive field decreases proportionally to the square root of the grain size.