Hard magnetic properties and coercivity mechanism of melt-spun Misch Metal-Fe-B alloy

Magnetic and structural properties of Misch Metal (MM)-Fe-B alloys, were examined in the melt-spun ribbons. Melt-spun MM-Fe-B samples were prepared at the surface velocities of 18-30 m/s. Crystalline structure and their room-temperature magnetization characteristics were analyzed, and the optimum surface velocity of 20 m/s and nominal composition of MM13Fe81B6 were obtained. Microstructural analyses indicate that the grain size is approximately 30-50 nm in the alloys with the optimum characteristics. In the MM16Fe78B6 alloys, Pr-rich and La-rich phases concentrated on grain boundaries, which resulted in the coercivity augment with the increase of MMFe2 content. Dependence of coercivity on applied magnetic field suggested that the mechanism of coercivity in moderate MM-content samples was inhomogeneous domain wall pinning type. The melt-spun ribbons in the optimum condition exhibit a coercive force of 6.9 kOe and an energy product of 8.5 MGOe, which can be used as the potential isotropy magnetic powders in the bonded magnets.