Crystal structure and magnetic properties of melt spun SmCo7−xMx (M=Ta, Cr, and Mo; x=–0.6) ribbons

The crystal structure and magnetic properties of melt spun SmCo7−xMx (M=Ta, Cr, and Mo; x=0–0.6) ribbons have been investigated. Based on x-ray diffraction analysis, it is found that a pure TbCu7-type structure is formed in the melt spun SmCo7−xTax (x=0–0.3) ribbons, while minor amount of additional 2:17 phase appears for the SmCo7−xMx (M=Cr and Mo; x=0.1–0.6) ribbons, implying that the elements in VIB group (Cr and Mo) are inferior to the element in VB group (Ta) in stabilizing metastable 1:7 phase. The result, analyzed by Rietveld refinement method, shows that Ta, Cr, and Mo may occupy the 2e site of 1:7 phase, which leads to the enhancement of the magnetic anisotropy field of 1:7 phase, just like Ti, Zr, Hf, Nb, or V did. From the magnetic performance point of view, with increasing the content of doping element x from 0 to 0.6, the maximum coercivity of SmCo7−xMx ribbons is enhanced from 1.9 kOe for binary SmCo7 to 11.3 kOe for M=Ta, 6.6 kOe for M=Cr, and 7.5 kOe for M=Mo, respectively, while the remanent magnetization is all reduced for the above ternary alloy ribbons.