High coercivity PrFeB magnetic nanoparticles by a mechanochemical method.

NdFeB nanoparticles are widely used because of their outstanding hard magnetic properties. In fact, PrFeB has higher magneto-crystalline anisotropy than NdFeB, which makes Pr-Fe-B a promising magnetic material. However, the chemical synthesis route to PrFeB nanoparticles is challenging because of the higher reduction potential of Pr, as well as the complex annealing conditions. In this work, PrFeB nanoparticles were successfully synthesized 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 CaH, which formed an embedded structure after ball milling. Then, PrFeB powder was synthesized a time-saving annealing process. The impact of the PrO content and the preparation conditions was investigated. The coercivity of the as-annealed powder with 100 wt% PrO excess is 18.9 kOe. After magnetic alignment, the coercivity, remanence, and maximum energy product were: 9.8 kOe, 78.4 emu g, and 9.8 MGOe, respectively. The present work provides a promising strategy for preparing anisotropic Pr-Fe-B permanent magnetic materials.