Effect of Nonmagnetic Hf Addition on Magnetic Properties of Melt-Spun Misch Metal-Fe-B Ribbons

Misch Metal (MM)-Fe-B magnets are proposed to develop permanent magnets with a high performance/cost ratio and to balance the disproportionate use of rare earth (RE) resources. To improve the magnetic performance of (MM)-Fe-B ribbons precursors of magnets, the addition of non-magnetic hafnium (Hf) was used. MM14Fe80-xHfxB6 (x = 0-3 at. %) ribbons were fabricated by melt-spinning technique at a wheel velocity of 35 m/s and were then annealed to obtain a nanocrystalline structure. The ribbons' magnetic properties, morphology, and structure were investigated methodically. It was found that the coercivity, Hc, of the MM14Fe80-xHfxB6 (x = 0-3 at. %) as-spun ribbons increased significantly from 5.85 kOe to 9.25 kOe with an increase in the Hf content from 0 to 2 at. %, while the remanence decreased slightly for the whole 0-3 range at. % Hf. The grain size of the RE2Fe14B phase gradually decreased as the Hf addition content increased from 0 to 3 at. %. As a result, the best combination of magnetic properties, such as Hc = 9.25 kOe, Mr = 87 emu/g, and maximum energy product (BH)max = 9.75 MGOe, was obtained in the ribbons with 2 at. % Hf addition was annealed at an optimal temperature of 650 degrees Celsius for 20 min. This work can serve as a useful reference for the further development of a new permanent magnet based on MM and Hf elements and can provide a feasible way for the efficient use of rare earth resources.