Coercivity enhancement and magnetization process in Mn55Bi45 alloys with refined particle size

Abstract The MnBi permanent magnetic alloys with high coercivity was prepared by a low-energy ball milling process. The coercivity of the MnBi alloys can be controlled by tuning the particle size and the size distribution of the MnBi alloys powders through the milling process. The size-dependent coercivity of the particles was expressed by a function of H c  = 10 6.17−0.56·log( D ) , where the particle size ( D ) was supposed to be lager than the single-domain size. With an optimized treatment, a room-temperature coercivity of ∼1.9 T was achieved in the MnBi powders. The magnetization curves and micromagnetic analyses indicated that the magnetization process of the MnBi alloys was governed by the coherent magnetization rotation. The hardening mechanism was corresponding to the nucleation process in the anisotropic MnBi powders with refined particle size.