Phase composition and magnetic properties of Pr–Nd–MM–Fe–B nanocrystalline magnets prepared by spark plasma sintering

The isotropic nanocrystalline [(PrNd)0.8MM0.2]29.8Fe68.7Al0.1Cu0.12Co0.88B magnets (MM: mischmetal) were prepared by single-main phase and double-main phase methods using spark plasma sintering (SPS). Melt-spinning method was used to prepare initial powder and avoid component deviations caused by longtime ball milling. The magnetic properties of the magnet prepared by double-main phase method (called double-main phase magnet, DMP magnet) are remanence of Br = 0.75 T, intrinsic coercivity of Hcj = 909.83 kA·m−1, maximum magnetic energy product of (BH)max = 95.48 kJ·m−3, which are better than those of the magnet prepared by single-main phase method (called single-main phase magnet, SMP magnet). The diffraction peaks of the main phase of DMP magnet split in X-ray diffractometer (XRD) pattern, indicating that R2Fe14B phases with different distributions of La/Ce elements exist in the magnet. This speculation is confirmed by transmission electron microscopy (TEM) observation. The La/Ce-rich main phase and La/Ce-lean main phase are present in DMP magnets. The heterogeneity of rare earth elements suppresses the magnetic dilution effect in DMP magnet, and the magnetic properties are improved. Though the DMP magnet contains different main phases, it presents unitary Curie temperature (TC) of 577 K, which is higher than that of SMP magnet. This result suggests that the TC of the magnets can be promoted by double-main phase method and SPS.