Homogeneous transformation of the grain boundary phase and Tb grain boundary diffusion optimization in sintered Nd-Fe-B magnet

To improve the efficient diffusion of Tb element, Cu nano powder is added to the grain boundary of sintered Nd-Fe-B magnet. (Nd, Tb) 2 Fe 14 B shell layer structure with high anisotropy is formed on the main phase after the Tb diffusion. The distribution depth of (Nd,Tb) 2 Fe 14 B shell layer increased from 50 μm for the standard magnet to 145 μm for 0.2 wt% Cu added magnet. Magneto-optical Kerr effect observations revealed that the reversal of magnetization is effectively hindered by the (Nd,Tb) 2 Fe 14 B structure which increased the intrinsic coercivity ( H cj ). The H cj increased from 16.07 kOe for the standard alloy to 24.38 kOe for diffusion magnets. The addition of Cu promoted the homogeneous transformation of the grain boundary phase from stable hexagonal-Nd 2 O 3 to metastable cubic-Nd 2 O 3 phase. The first-principles calculations showed that the diffusion barrier of Tb atom in the grain boundary phase reduced from 0.89 to 0.67 eV. The mechanism of magnetic domain movement with (Nd,Tb) 2 Fe 14 B core-shell structure is analyzed in detail. • Cu nanoparticles are added into Nd-Fe-B magnets to improve the efficiency of grain boundary diffusion (GDB). • The homogeneous transformation of the grain boundary phase greatly promoted the GDB efficiency of the Ne-Fe-B magnet. • The migration behavior of Tb atoms in GDB process is obtained by first-principles calculations. • The magnetic domain mechanism and reversal behavior of (Nd,Tb) 2 Fe 14 B core-shell structure are analyzed emphatically.