Great influence of demagnetization history on internal interaction and magnetization process of mischmetal-based magnets

The magnetization process and corresponding magnetization curve are usually used to analyze the coercivity mechanism of Nd-Fe-B based sintered magnet. However, different demagnetization histories will seriously influence the magnetization curve, leading to an inaccurate understanding and analysis of magnetization process. In this work, we investigated the magnetization behavior of multi-main phase (MMP) magnets with thermal demagnetized and alternating current demagnetized states. Recoil curves of initial magnetization process and demagnetization process of thermal demagnetized magnets reflect the movement of domain walls inside the grains and the magnetization interaction between the grains, respectively. It is noted that the former process cannot represent the magnetization reversal of the entire magnet, which is not appropriate to analyze coercivity mechanism alone. While the recoil curves of both two processes of AC demagnetized magnets can illustrate the magnetization reversal of the entire grains and the interaction between grains. Magneto-optical Kerr microscope shows that the grains of thermal demagnetized magnets are in multi-domain states, and the grains of AC demagnetized magnets are almost in single-domain states. Domain walls of thermal demagnetized magnets move easily within the grains, which is more conducive to magnetization saturation in industrial production. In addition, the minorloops of thermal demagnetized magnets can independently represent the transition of grains from multi-domain to single-domain and the demagnetization of single-domain grains, which is equivalent to characterizing the internal interactions by recoil curves. The investigation of magnetization characteristics of MMP sintered magnets starting from different demagnetized states is helpful to further understand the internal interaction and magnetic hardening mechanism.