Micromagnetic simulations on the grain size dependence of coercivity in anisotropic Nd–Fe–B sintered magnets

Micromagnetic simulations of magnetization reversals of Nd–Fe–B anisotropic magnets with exchange-coupled grains demonstrate that the local demagnetization factor decreases as the grain size is reduced. This explains the higher coercivity and the lower temperature dependence of coercivity in magnets with smaller grain sizes. When a fraction of Nd2Fe14B grains become a single domain state for average grain sizes <1 μm, a higher magnetic field is needed to magnetize them, giving rise to a two-step initial magnetization curve.