Influence of misch metal content on microstructure and magnetic properties of R-Fe-B magnets sintered by dual alloy method

MM₁₄Fe_79.9B_6.1/Nd_13.5Fe_80.5B₆ magnets were fabricated by dual alloy method (MM, misch metal). Some magnets have two Curie temperatures. Curie temperatures T_c1 corresponds to the main phase which contains more LaCe, and T_c1 decreases from 276.5 °C to 256.6 °C with the content of MM increasing from 30.3 at.% to 50.6 at.%. The variation of B_r with the increase ofMMindicates the existence of inter-grain exchange coupling in the magnets. When MM/R ≤30.3 at.%, the magnetic properties can reach the level of the intrinsic coercivity H_cj ≥7.11 kOe and the maximum energy product (BH)max ≥41 MGOe. Compared with Nd, La and Ce are easier to diffuse to the grain boundaries in the sintering process, and this will cause the decrease of H_cj. Due to the diffusion between the grains, the atomic ratio of La, Ce, Pr, and Nd in each grain is different and the percentage of Nd in all grains is higher than that in misch metal.