Structural and magnetic properties of SmCo_7-xMo_x alloys

Phase structure and magnetic properties of the as-cast and as-milled/annealed SmCo_7-xMo_x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys have been systematically studied. It is found that all the as-cast series alloys are composed of the CaCu₅-type and Th₂Zn ₁₇-type phases. Saturation magnetization of the samples decreases with the Mo content increasing. Intrinsic coercivities (_iH _c) of no more than 0.06 Tare observed in these as-cast samples, due to their rather coarse grain microstructures with an average grain size of 50 μm. The as-milled/annealed SmCo_7-xMo_x 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 _iH_c (≥ 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 nanogram boundaries. The temperature coefficient (β) of the _iH _c is about -0.22%/°C in the temperature range of 25-400°C for the as-milled/annealed samples.