Internally Segmented Nd-Fe-B/CaF Sintered Magnets

Dielectric CaF₂ layers were introduced into Nd-Fe-Co-Ga-B green compacts which were subsequently sintered into internally segmented anisotropic magnets. Layers with the nominal area density of 0.2-0.3 mg CaF ₂ per mm ² were found to increase the electrical resistivity by two orders of magnitude while still allowing the magnets to be cut and polished. The internal segmentation with CaF ₂ fully preserves the coercivity of the magnets and is accompanied by only a small decline of the magnet remanence. The fcc Nd_1-x Cax (F,O)_δ phase produced by the reaction between the CaF ₂ phase and the Nd-rich phase is believed to improve the metallurgical bond between the dielectric layers and magnet matrix. The internal segmentation may be a cost-effective way of manufacturing Nd-Fe-B sintered magnets with low eddy current losses, suitable for motor/generator applications.