Structure and magnetic properties of nanostructured PrCo7-xTix(x=0-0.4) prepared by mechanical milling and subsequent annealing

The Pr(Co,Ti)7 phase alloy, which can not be prepared directly by arc melting, has been synthesized by mechanical milling and subsequent annealing. A coercivity of 7.3 kOe, remanence ratio of 0.69 and maximum energy product of 10.6 MGOe have been achieved for the PrCo6.7Ti0.3 powder milled for 3 h and annealed at 800 deg. C for 3 min. The high coercivity obtained indicates that the addition of Ti causes the anisotropy of PrCo7 phase to change from planar to uniaxial. Transmission electron microscopy reveals that a uniform Pr(Co,Ti)7 microstructure with an average grain size of about 20 nm is developed in the powders. The electron energy-loss spectrum acquired from one grain proves that the Ti enters the Pr(Co,Ti)7 grain. The high coercivity obtained apparently arises from the high uniaxial anisotropy of Pr(Co,Ti)7 phase and the uniform nanoscale microstructure developed by mechanical milling and subsequent annealing