Development of Mischmetal-(FeCo)-B Ribbons with Improved Magnetic Properties by Addition of Si

In order to develop mischmetal-based permanent magnets with a high performance/cost ratio, Si addition was employed to enhance the magnetic performance of the MM₁₆Fe_76-xCo₂Si_xB₆ (x = 0–1.5%) ribbons. The ribbons were manufactured by a melt-spinning technique at different velocities. Samples were studied in an as-cast state and after annealing. It was found that the addition of Si in the MM₁₆Fe_76-xCo₂Si_xB₆ ribbons increased the exchange interaction between Fe atoms in the 2:14:1 phase, reduced the crystal grain size, and increased the exchange coupling between the crystal grains; as a result, the magnetic properties were improved. The coercivity and Curie temperature increased with the increasing Si content from x = 0 to x = 1.5 at%, while the remanence and energy product increased with the addition of Si up to 1% and decreased with further Si addition. The best combination of magnetic properties, such as coercivity of H_c = 8.9 kOe, remanence Mr = 98 emu/g, Curie temperature T_c = 257 °C, and energy product (BH)_max = 13.84 MGOe, were obtained in ribbons with 1.0 at. % Si. Thus, it is demonstrated that the addition of Si leads to an improvement of the magnetic properties of MM₁₆Fe_76-xCo₂Si_xB₆ ribbons, making them good candidates as precursors for the preparation of permanent magnets with an energy product between that of ferrites and Nd-Fe-B magnets.