“…As an extrinsic magnetic property, the coercivity of a magnet is not only associated with the intrinsic magnetic properties of the material, but can also be influenced by the microstructure of the magnet, such as grain size, shape, and boundary, and phase interfaces [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. Concentrating the HRE elements at the grain surfaces forming a core-shell structure by diffusing the HRE along the grain boundaries into the τ1-phase grains, known as the grain boundary diffusion process (GBDP), is an effective method to increase coercivity [ 10 , 14 ].…”