Temperature dependence of magnetization reversal mechanism in misch-metal substituted Nd-Fe-B magnets sintered by dual alloy method

The substitution of Nd by misch-metal (MM) in Nd-Fe-B permanent magnets has attracted extensive attention due to the effective reduction of production cost and rational utilization of rare earth resources. In particular, multi-main phase (MMP) magnets prepared by dual alloy method possess a higher permanent magnetic performance than that of single main phase (SMP) magnets. However, the coercivity mechanism of MMP magnets is different from the nucleation and propagation of SMP magnets, especially the interactions of different 2:14:1 main phases have not been clarified. In this study, we investigated the temperature dependence of magnetization reversal mechanism in (MM,Nd)-Fe-B magnets by using recoil loops, minor hysteresis loops, first-order and second-order reversal curves. It found that with the increase of temperature, the magnetic moments motion is mainly affected by long-range magnetostatic interaction rather than exchange coupling. The weakened coupling interaction makes the demagnetization process of softer and harder magnetic phases asynchronous. The thermal activation energy barrier index related to coercivity mechanism is 1.45, 1.18 and 1.0 at 200 K, 300 K and 380 K, respectively. It indicates that nucleation and expansion of reversed domains are the main mechanisms controlling the magnetization reversal process at low temperature. While the coercivity at high temperature is mainly determined by the domain wall pinning mechanism. In addition, we noted that both two coercivity mechanisms coexist in MMP magnets at 300 K. Micromagnetism has also been used to verify the coercivity mechanism of (MM,Nd)-Fe-B magnets sintered by dual alloy method, which is of great significance for improving the magnetic properties of high abundance rare earth magnets.