Grain Interface Modification and Magnetic Properties of Nd–Fe–B Sintered Magnets

Effective grain interface modification was conducted to increase the coercivity of Nd–Fe–B sintered magnets without degrading their magnetic properties seriously. The surface of magnet pieces (3.0×3.0×2.8 mm3) was uniformly coated with a Dy or Tb metal film, and then each metal was introduced inside the magnets through the Nd-rich grain boundary regions for enriching them on the surface around the Nd2Fe14B grain particles. The coercivities of the Dy- and Tb-metal-treated magnets (HcJ = 1.45 and 1.81 MA/m, respectively) were considerably improved compared with that of the untreated magnet (HcJ = 0.98 MA/m), suggesting that the aligned magnetic domain structure was effectively stabilized by such a Dy- or Tb-enriched interface around the Nd2Fe14B grain particles.