Nanocrystalline Pr0.5Sm0.5Co5 alloy obtained by mechanical milling

Starting from arc-melted alloys, nanostructured Pr0.5Sm0.5Co5 powders were synthesized by mechanical milling and subsequent vacuum annealing during short times to develop an optimal microstructure with high hard magnetic properties. The best magnetic properties were obtained for the stoichiometric Pr0.5Sm0.5Co5 powders milled for 4 h and annealed at 800 deg. C for 1 min with a high coercitivity of 13.5 kOe, a high Mr/Mmax ratio of 0.72 and a maximum energy product of 11 MGOe. From X-ray diffraction and transmission electron microscopy, CaCu5-type phase and an average grain size of about 12 nm were determined in the annealed powders, and we calculated that 59% of the volume of the grains/crystallites are exchange-coupled. The observed magnetic hardening is associated to the high magnetic anisotropy field of the PrCo5 and SmCo5 phases and also to the microstructure developed by the processing used