Nd-Fe-B sintered magnet has been used for various applications such as sensors, actuators and the motors for hybrid vehicles (HVs) and electric vehicles (EVs), because of the highest maximum energy product (BH)_(max) among permanent magnets. However, due to the scarce and localized natural resources of the heavy rare earth (HRE) elements, many efforts have been done to reduce the usage of Dy in the Nd-Fe-B magnets. It is well known that the microstructure of Nd-Fe-B sintered magnet is composed of Nd_2Fe_(14)B main phase and the grain boundary phase. The grain boundary phases such as Nd-rich phase and B-rich phase play an important role to get high coercivity of Nd-Fe-B sintered magnet, and these microstructures are thought to deeply related to the magnetic properties.
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