Abstract: The growing demand in sustainable technology and clean energy applications highly require for developing high-performance Nd-Fe-B permanent magnets. The magnetic properties and microstructures of the Nd_10.23Pr_2.56Fe_68.32Co_13.08B_5.81 (A0 alloy), Nd_10.18Pr_2.55Fe_67.98Co_13.01B_5.78Nb_0.50 (A-Nb0.5 alloy), and Nd_10.18Pr_2.55Fe_67.98Co_13.01B_5.78Ga_0.50 (A-Ga0.5 alloy) are investigated. We use the strategy of grain refinement and tuning intergranular phase (IP) to improve the magnetic properties by doping high melting point element (HMPE) Nb and low melting point element (LMPE) Ga. The average grain size of Nd₂(Fe, Co)₁₄B (2:14:1) in the A0 alloy is 52 ± 2 nm, and it is effectively reduced to 40 ± 3 and 32 ± 3 nm through Nb/Ga addition. The atom probe tomography (APT) is used to illustrate the effect of the IP on magnetic properties. Both ferromagnetic and non-ferromagnetic IPs are observed in the A0 alloy, while only ferromagnetic IP is shown in the A-Nb0.5 and A-Ga0.5 alloys. Moreover, the concentration of (Fe + Co) at ferromagnetic IP is increased through Nb/Ga addition. The synergistic effects of grain refinement and tuning intergranular phase lead to the improvement of the remanence (B_r) and maximum energy product ((BH)_max). In comparison to the A0 alloy, B_r is increased to 0.85 T of the A-Nb0.5 alloy and 0.88 T of the A-Ga0.5 alloy. The (BH)_max is improved by 8.8 % to 123 kJ/m³ for the A-Nb0.5 alloy and by 21.2 % to 137 kJ/m³ for the A-Ga0.5 alloy. Our findings provide an approach to develop high-performance rare-earth permanent magnets by grain refinement and adjusting the intergranular phase.

Key words: Rare earth permanent magnetic material, Magnetic property, Grain refinement, Intergranular phase, Atom probe tomography