A comparative study on the microstructure and magnetic properties of melt-spun RE2Fe14B/α-Fe and RE2Fe14B/Fe3B (RE=Nd, Pr) nanocomposites

The microstructure and magnetic properties of melt-spun RE₂Fe₁₄B/α-Fe and RE₂Fe₁₄B/Fe₃B nanocomposite powders were studied using Pr and Nd versions of RE₉Fe₈₆B₅(RE₂Fe₁₄B/α-Fe) and RE₉Fe₇₉B₁₂(RE₂Fe₁₄B/Fe₃B) alloys. It was found that the RE₉Fe₈₆B₅ exhibited a finer and more uniform microstructure with an average grain size of ∼10 nm, whereas a relatively coarse microstructure (grain size up to 100 nm) was observed in the RE₉Fe₇₉B₁₂. It was also found that the RE₉Fe₈₆B₅ yielded higher B_r and (BH)_max, and a more square demagnetization loop, although the H_ci was slightly lower. The superior magnetic properties observed in the RE₉Fe₈₆B₅ can be attributed to the more favorable intrinsic magnetic properties of α-Fe (higher M_s and lower K) and the much finer microstructure, which produces a stronger intergrain exchange coupling between the RE₂Fe₁₄B and α-Fe phases. The results indicate that RE₂Fe₁₄B/α-Fe nanocomposites are more desirable than RE₂Fe₁₄B/Fe₃B for future development of RE-Fe-B nanocomposite magnets.