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In order to obtain high magnetic properties in Ce–Pr–Nd–Fe–B spark plasma sintered (SPSed) magnets, the alloys were introduced by the dual-alloy method. The relationship of microstructure, magnetic properties, and thermal stability was investigated. The remanent magnetization, coercivity, and maximum energy product were sharply enhanced from 0.68 T, 653 kA/m, and 75.62 kJ/m3 to 0.80 T, 865 kA/m, and 104 kJ/m3 for the magnets that with 0 and 75 wt.% Pr–Fe–B addition. The Curie temperature also increased from 542 K to 563 K after adding Pr–Fe–B alloys. The scanning electron microscopy (SEM) analysis showed that, during the sintering process, the rare-earth elements migrated into the flake boundary and diffused in 2:14:1 main phases; thus, (Ce, Pr, Nd)2Fe14B hard magnetic phases were formed, which is helpful to optimize the microstructure and magnetic properties. An enhancement of exchange coupling among the grains of SPSed magnets was obtained as a result of grain refinement by adding Pr–Fe–B alloys. [ABSTRACT FROM AUTHOR]

The grain boundary diffusion process (GBDP) has become an important technique in improving the coercivity and thermal stability of Dy-free sintered Nd-Fe-B magnets. The influence of Dy70Al10Ga20 and (Pr75Dy25)70Al10Ga20 alloys by the GBDP on sintered Nd-Fe-B magnets are investigated in this paper. After diffusing Dy70Al10Ga20 and (Pr75Dy25)70Al10Ga20 alloys, the coercivity (Hcj) of the magnets increased from 13.58 kOe to 20.10 kOe and 18.11 kOe, respectively. Meanwhile, the remanence of the magnets decreased slightly. The thermal stability of the diffused magnets was improved by the GBDP. The microstructure shows continuous Rare-earth-rich (RE-rich) grain boundary phases and (Dy, Pr/Nd)2Fe14B core-shell structures which contribute to improving the coercivity. Moreover, the Dy concentration on the surface of the (Pr75Dy25)70Al10Ga20 diffused magnets decreased with the Pr substitution for the Dy element. The openness of the recoil loops for the (Pr75Dy25)70Al10Ga20 diffused magnets is smaller than that of the original magnets and Dy70Al10Ga20 diffused magnets. The results show that the (Pr75Dy25)70Al10Ga20 alloys can effectively optimize the microstructure and improve the magnetic properties and thermal stability of the sintered Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]

• Nanocomposite Nd-Fe-B/Alnico are fabricated by combining Nd-Fe-B and Alnico alloys. • A novel core shell structure is formed in the alloys consisting of 2:14:1 phase as core and Alnico rich phase as shell. • No kink in the demagnetization curves was observed indicating the strong exchange interactions among the phases. • Curie temperature of the alloys increased from 581 K to 654 K, and the spin reorientation temperature decreased from 130 K to 116 K. • Highest energy density of ～150 kJ/m3 is obtained in the best alloy. Nd-Fe-B alloys have high intrinsic coercivity, high magnetic energy density, but low Curie temperature and poor temperature stability. While Alnico alloys have high Curie temperature and high temperature stability, but low intrinsic coercivity and low magnetic energy density. It would be of great scientific, technological and economical interest if these two alloys could be combined together in some proportion to make composite magnets with good comprehensive properties. Here we report nanocrystalline composite magnets containing Nd-Fe-B hard phase and alnico semi-hard phase fabricated by melt-spinning technique. A novel core-shell like structure constituting Nd-Fe-B (2:14:1) phase as core and Alnico rich phase as shell was obtained by optimizing the composition and processing conditions. The maximum energy density was enhanced upto 150 kJ/m3 in nanocomposite magnets. The Curie temperature of the main phase increased to 654 K for Nd-Fe-B/Alnico from 581 K for pure Nd-Fe-B alloy, which is attributed to the molecular field penetration of Alnico phase into the hard 2:14:1 phase, in addition to the substitution of Fe by Co and Ni. No kink or dip was observed in the demagnetization curves, which suggested the presence of strong exchange interactions among the phases of the nanocomposite alloys. [ABSTRACT FROM AUTHOR]