Nanocomposite PrCo5/Pr2Co17 magnets with enhanced maximum energy product

Nanocomposite PrCo5/Pr2Co17 powders, with different volume fraction of the Pr2Co17 phase, were synthesized by mechanical milling mixtures of PrCo5 and Pr2Co17 alloy powders with the aim of enhancing the maximum energy product of PrCo5-based powders. It is found that the saturation magnetization increases monotonously with the volume fraction of the Pr2Co17 phase while the coercivity decreases. As a result, the maximum energy product first increases with the Pr2Co17 phase, going through a broad peak, and then decreases with further increase of the Pr,Co,, phase. The highest maximum energy product of 11.8 MG Oe is obtained in a mixture consisting of 70% PrCo5 and 30% Pr2Co17 phase. Microstructural studies reveal that a uniform nanoscale PrCo5/Pr2Co17 microstructure with an average grain size of about 20 nm is developed in these PrCo5/Pr2Co17 powders. Evidence of intergranular exchange coupling is found in the PrCo5/Pr2Co17 powders, suggesting that the enhanced energy product is due to exchange coupling between the magnetically hard PrCo5 and soft Pr2Co17 nanograins. (C) 2000 Elsevier Science B.V. All rights reserved.