Synergistic effects of La, Ce and Ga multi-elements in Nd–La–Ce–Fe–Ga–B sintered magnet

• Synergistic effects of La, Ce and Ga multi-elements on Nd–La–Ce–Fe–Ga–B magnets are revealed. • Comprehensive magnetic properties with H cj = 12.2 kOe, B r = 13.0 kG, ( BH ) max = 39.2 MGOe, and T C = 285 °C are obtained in annealed La15 magnet. • Increasing La substitution for Ce manipulates the formation, distribution and magnetism of REFe 2 and RE 6 Fe 13 Ga intergranular phases. • Coercivity increment Δ H max of annealed magnet is positively associated with the fraction of newly formed REFe 2 phase f REFe2 . • La substitution facilitates the formation of La-containing RE 6 Fe 13 Ga phase with magnetic transformation from anti-ferromagnetic to ferromagnetic state. Through a comparative study of (La x Ce 100-x ) 9.6 (Pr 20 Nd 80 ) 22.4 Fe bal Ga 0.5 M 1.3 B 0.9 (x = 0, 5, 15, 35, La + Ce/total rare earth = 30 wt%) as-sintered and annealed magnets, we reveal the synergistic effects of La, Ce and Ga multi-elements that enable preferable remanence of 13.0 kG, maximum energy product of 39.2 MGOe, coercivity of 12.2 kOe and Curie temperature of 285 °C of optimally annealed La15 magnet (x = 15). Results show that increasing La substitution for Ce manipulates the REFe 2 (RE = rare earth) and RE 6 Fe 13 Ga intergranular phases. On one hand, REFe 2 phase is progressively inhibited and almost disappears in as-sintered La15 magnet, with resultant coercivity deterioration to 6.7 kOe. After post-sinter annealing, the coercivity increment Δ H max is positively associated with the fraction of newly formed non-ferromagnetic REFe 2 phase f REFe2 . On the other hand, higher La substitution in optimally annealed La35 magnet (x = 35) stabilizes the La-containing RE 6 Fe 13 Ga intergranular phase, which is ferromagnetic as uncovered by Lorentz TEM and supported by first-principle calculation. New understandings on the synergistic effects of multi-elements delight future work towards delicately controlling the microstructure and optimizing the performance of Nd–La–Ce–Fe–Ga–B sintered magnets.