The role of grain size distribution on magnetic properties of sintered Nd–Fe–B magnets

The influence of grain size distribution for sintered Nd–Fe–B magnets is investigated using computational micromagnetics. The standard deviation of grain size distribution is selected as a quantity that can measure an inhomogeneity in grain size. Micromagnetic models with different standard deviations are created, which consist of irregularly shaped grains and grain boundaries (GBs). For micromagnetic models responsible for grain size distribution, the dependence of the coercivity on the standard deviation is discussed based on finite element based micromagnetic simulations. The micromagnetic simulations show little dependence of coercivity on the standard deviation for the ferromagnetic GB phase but reveal significant changes in coercivity for the non-ferromagnetic GB phase. The simulated results show that the standard deviation characterizing grain size distribution can be considered as a microstructural index concerning the magnetic properties of sintered Nd–Fe–B magnets.