High coercivity Pr₂Fe₁₄B magnetic nanoparticles by a mechanochemical method

Nd₂Fe₁₄B nanoparticles are widely used because of their outstanding hard magnetic properties. In fact, Pr₂Fe₁₄B has higher magneto-crystalline anisotropy than Nd₂Fe₁₄B, which makes Pr-Fe-B a promising magnetic material. However, the chemical synthesis route to Pr₂Fe₁₄B nanoparticles is challenging because of the higher reduction potential of Pr³⁺, as well as the complex annealing conditions. In this work, Pr₂Fe₁₄B nanoparticles were successfully synthesized via an efficient and green mechanochemical method consisting of high energy ball milling, annealing, and a washing process. Microstructural investigations revealed that the oxide precursors were uniformly wrapped by CaO and CaH₂, which formed an embedded structure after ball milling. Then, Pr₂Fe₁₄B powder was synthesized via a time-saving annealing process. The impact of the Pr₂O₃ content and the preparation conditions was investigated. The coercivity of the as-annealed powder with 100 wt% Pr₂O₃ excess is 18.9 kOe. After magnetic alignment, the coercivity, remanence, and maximum energy product were: 9.8 kOe, 78.4 emu g^-1, and 9.8 MGOe, respectively. The present work provides a promising strategy for preparing anisotropic Pr-Fe-B permanent magnetic materials.