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• The effects of annealing on the microstructures and magnetic properties of Ga and Cu co-added Nd-Fe-B magnet were investigated. • The intrinsic coercivity increases from 9.17 kOe to 18.67 kOe after annealing, which shows an increment of 103.5%. • The main reasons for the substantial increase of intrinsic coercivity are discussed. Post-sinter annealing is essential to improve the microstructures and magnetic properties in NdFeB-based sintered permanent magnetic materials. In this paper, investigated systemically are the effects of post-sinter annealing on the microstructures and magnetic performance of Ga and Cu co-doping Nd 2 Fe 14 B based sintered magnets. It is found out that the intrinsic coercive force of the magnets increased from 9.17 kOe to 18.67 kOe after two stage post-sinter annealing (PSA), which shows an extraordinary increment of 103.5%. The remanence, with a decreasing percentage of 1.95%, slightly decreases from 13.87 kGs to 13.60 kGs. The substantial increase of intrinsic coercivity is mainly attributed to the improvement of clean and thin continuous grain boundary layers, the smoothness of hard magnetic matrix phase and the appearance of the RE 6 (Fe, M) 14 antiferromagnetic phase during annealing. The reduction of the remanence is caused by the deteriorated orientation degree and reduced volume fraction of hard magnetic main phases after post-sinter annealing. [ABSTRACT FROM AUTHOR]

• Ce-Fe-B/Alnico composite spark plasma sintered magnets have been fabricated. • The two phases exit in the alloys interacting magnetostatically. • The Alnico phase constitutes α 1 and α 2 phases. • The Ce-Fe-B phase contained Ce 2 Fe 14 B and CeFe 2 phases. • Anisotropy variations in the recoil loops were observed at high applied magnetic field. By combining rare earth-based Ce-Fe-B and rare earth free Alnico powders, composite Ce-Fe-B/Alnico spark plasma sintered (SPS) magnets have been fabricated and reported for the first time. It is observed that the two phases exit in the alloys interacting magnetostatically. The Alnico phase constitutes α 1 and α 2 phases as a consequence of spinodal decomposition process, while the Ce-Fe-B phase contained Ce 2 Fe 14 B and CeFe 2 phases. By increasing the content of Alnico phase, the remanence magnetization and the maximum energy density of the composite alloys increased owing to the higher saturation magnetization of Alnico phase. Magnetic properties, such as remanence magnetization J s = 0.93 T, intrinsic coercivity H cj = 202 kA/m and maximum energy density (BH) max = 19.8 kJ/m3 were obtained in spark plasma sintered composite magnets containing 15 wt% Alnico. The recoil loops demonstrated the presence of anisotropy variations in the alloys specifically at high applied magnetic field. Analysis of the Curie temperature and elemental analysis validated that the constituent phases of SPS magnets exist in the alloys. This work may shed light on the development of composite magnets with distinct phases and enhanced magnetic properties. [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]