Micromagnetic Investigation of the Effect of Main-Phase Distribution on the Coercivity of Nd2Fe14B/Dy2Fe14B Exchange-Coupled Magnets

The spatial distribution of different hard magnetic phases is a key factor affecting the coercivity of dual-main-phase rare-earth permanent magnets. However, the underlying relationship between main-phase distribution and magnetization reversal behavior in Nd2Fe14B/Dy2Fe14B magnets remains unclear. In this work, micromagnetic simulations based on MuMax3 and OOMMF are performed to systematically investigate the effects of main-phase spatial arrangement on the magnetic properties and magnetization reversal mechanisms of Nd2Fe14B/Dy2Fe14B exchange-coupled magnets. First, single-phase Nd2Fe14B and Dy2Fe14B models are constructed to clarify the intrinsic magnetic characteristics of the two phases. The calculated demagnetization curves show that, although the magnetocrystalline anisotropy field HA of Nd2Fe14B is lower than that of Dy2Fe14B, its higher saturation magnetization MS results in a slightly larger anisotropy constant K, according to K = 12µ0·HA·MS. Nevertheless, Dy2Fe14B exhibits a stronger resistance to magnetization reversal, as reflected by its higher nucleation field HN and coercivity HC. This indicates that the resistance to magnetization reversal is more directly associated with HA than with K alone. Subsequently, three types of exchange-coupled dual-main-phase Nd2Fe14B/Dy2Fe14B magnet models, including cubic, cylindrical, and sandwich structures, are constructed with identical size fractions of the two phases to investigate the influence of phase spatial distribution on magnetization reversal behavior. The calculated results demonstrate that placing the Dy2Fe14B phase in the outer region leads to higher HNand HC than the reverse phase arrangement, owing to its higher HA, which strengthens the resistance against magnetization reversal. Further analysis of the in-plane magnetic-moments and angular distributions reveals that magnetic-moment deviation is initially activated in the Nd2Fe14B region with lower HA, followed by gradual propagation through exchange coupling at the phase interface. This effect of phase spatial distribution is not limited to Nd2Fe14B/Dy2Fe14B exchange-coupled magnets. In Nd2Fe14B/La2Fe14B and Nd2Fe14B/SmCo exchange-coupled magnets, placing the phase with the higher HA in the outer region likewise results in higher HNand HC than the reverse phase arrangement. In addition, for all the dual-main-phase exchange-coupled magnets considered above, the coercive field decreases with increasing magnet size. These findings provide theoretical insights into the regulation of coercivity through spatial phase distribution in dual-main-phase rare-earth permanent magnets.