Magnetic properties and rare earth element diffusion behavior of hot-deformed nanocrystalline dual-main-phase Nd–Ce–Fe–B magnets

To inhibit the magnetic dilution effect of Ce in Nd–Ce–Fe–B magnets, a dual-alloy method is employed to prepare hot-deformed dual-main-phase (DMP) magnets using mixed nanocrystalline Nd–Fe–B and Ce–Fe–B powders. A REFe(2) (1 : 2, where RE is a rare earth element) phase can only be detected when the Ce–Fe–B content exceeds 30 wt%. The lattice parameters of the RE(2)Fe(14)B (2 : 14 : 1) phase exhibit non-linear variation with the increasing Ce–Fe–B content due to the mixed valence states of Ce ions. Owning to inferior intrinsic properties of Ce(2)Fe(14)B compared to Nd(2)Fe(14)B, the magnetic properties of DMP Nd–Ce–Fe–B magnets almost decrease with the increase of Ce–Fe–B addition, but interestingly, the magnet with 10 wt% Ce–Fe–B addition exhibits an abnormally increased intrinsic coercivity H(cj) of 1215 kA m(−1), together with the higher temperature coefficients of remanence (α = −0.110%/K) and coercivity (β = −0.544%/K) in the temperature range of 300–400 K than the single-main-phase (SMP) Nd–Fe–B magnet with H(cj) = 1158 kA m(−1), α = −0.117%/K and β = −0.570%/K. The reason may be partly attributed to the increase of Ce(3+) ions. Different from the Nd–Fe–B powders, the Ce–Fe–B powders in the magnet are difficult to deform into a platelet-like shape because of the lack of low melting point RE-rich phase due to the precipitation of the 1 : 2 phase. The inter-diffusion behavior between the Nd-rich region and Ce-rich region in the DMP magnets has been investigated by microstructure analysis. The significant diffusion of Nd and Ce into Ce-rich and Nd-rich grain boundary phases, respectively, was demonstrated. At the same time, Ce prefers to stay in the surface layer of Nd-based 2 : 14 : 1 grains, but less Nd diffuses into Ce-based 2 : 14 : 1 grains due to the 1 : 2 phase presented in the Ce-rich region. The modification of the Ce-rich grain boundary phase by Nd diffusion and the distribution of Nd in the Ce-rich 2 : 14 : 1 phase are beneficial for magnetic properties.