Sensitivity of coercivity and squareness factor of a Nd-Fe-B sintered magnet on post-sintering annealing temperature

Abstract An N38SH-grade magnet with low oxygen content was used to study the evolution of magnetic properties upon post-sintering annealing. Phase transformation of as-sintered magnet was investigated by differential scanning calorimetry (DSC). Three low temperature eutectic transition points were detected. Little change could be found when annealed below the lowest eutectic transition point. A wide annealing temperature range (460-560 °C) between the lowest and highest eutectic transition point was available for this magnet to achieve a relatively high coercivity (∼1671 kA/m) at a relatively low Dy content (∼3 wt.%). However, squareness factor (SF) of the demagnetizing curve and its temperature stability were found to decrease after annealing above the highest eutectic transition point. This was attributed to the change of Cu content in the Nd-rich phase under different annealing temperatures.