Coercivity enhancement of low rare earth Nd-Fe-B sintered magnets by optimizing microstructure

Magnetic performance of Nd-Fe-B sintered magnets, especially the coercivity is highly sensitive to microstructures extrinsically. To enhance coercivity of the near-stoichiometric Nd₂Fe₁₄B magnet (Nd, Pr)_12.5Fe_balB_6.1 (at%), the microstructure is optimized by varying sintering condition. At lower sintering temperatures, full densification cannot be reached even prolonging the sintering time, the coupling between adjacent 2:14:1 phase grains results in a low coercivity. At higher sintering temperatures, the grains of 2:14:1 phase grow up quickly, also deteriorating the coercivity. At an optimum sintering temperature of 1050 °C, the magnet reaches a full densification with most 2:14:1 phase grains of 4-5 μm, showing a high coercivity of 16.4 kOe. The formation of smooth and continuous grain boundary RE-rich phase reduces the magnetic interactions and the grain refinement hinders nucleation of reversed domains at low fields, respectively.