Structural and magnetic properties of SmCo7-xMox alloys

Phase structure and magnetic properties of the as-cast and as-milled/annealed SmCo7-xMox (x=,0.,0.,0.,0.4) alloys have been systematically studied. It is found that all the as-cast series alloys are composed of the CaCu5-type and Th2Zn17-type phases. Saturation magnetization of the samples decreases with the Mo content increasing. Intrinsic coercivities (iHc) of no more than 0.06 T are observed in these as-cast samples, due to their rather coarse grain microstructures with an average grain size of 50 mum. The as-milled/annealed SmCo7-xMox powders crystallize in the disordered TbCu7-type (1:7) structure with very fine nanograins, and a minor Co3Mo phase appears in the samples with x=0.1-0.4. High iHc (0.95 T) are achieved in these samples, with a maximum of 1.26 T located at x=0.2, which can be primarily attributed to strong pinning of the domain wall motion at the nanograin boundaries. The temperature coefficient (beta) of the iHc is about -0.22%/ deg C in the temperature range of 25-400 deg C for the as-milled/annealed samples.