High coercivity in nanostructured PrCo5-based powders produced by mechanical milling and subsequent annealing

Nanostructured PrCo5-based PrxCo100-x (x = 15.4-20.5) powders have been synthesized by mechanical milling and subsequent annealing cast alloys. The best overall properties have been developed in stoichiometric PrCo5 powders milled for 4 h and annealed at 800 degrees C for 1 min with a high coercivity of 16.3 kOe along with a high M-r/M-s ratio of 0.66 and medium-strength maximum-energy product of 11.6 MGOe. The highest coercivity of 23.7 kOe has been obtained in Pr19Co81 powders. Microstructural studies reveal that a uniform PrCo5 microstructure with an average grain size of about 15 nm is developed in the powders, which have an average particle size of about 5 mu m. The observed magnetic hardening is believed to arise from the high anisotropy field of the PrCo5 phase and the uniform nanoscale microstructure developed by the processing used. (C) 1999 American Institute of Physics. [S0003-6951(99)02446-8].