We investigated the mechanisms of coercive force enhancement on Nd 11 Dy 4 Fe 76.5 TM 2.5 B 6 (TM = Co, Cu, Al) induced by a number of cyclic heat treatments (CHT) at temperatures from 350°C to 450°C. The difference in thermal expansion coefficients between Nd-rich and Nd 2 Fe 14 B phases induced penetration of the Nd-rich phase into the Nd 2 Fe 14 B grain boundary through capillary force and compress pressure by CHT. Also, dislocations in the Nd 2 Fe 14 B grain were formed by thermal stresses from thermal expansion and contraction, which caused the domain wall pinning effect. Consequently, coercivity was enhanced from 2,303 kA/m before CHT to 2,480 kA/m after CHT, and a remanence of 1.18 T was maintained after two cycles.