Effect of Ge on the magnetic properties and crystal structure of melt spun SmCo7–xGex ribbons

The effect of Ge on the magnetic properties and crystal structure of melt spun SmCo7–xGex (x = 0–0.8) ribbons have been investigated. SmCo7–xGex ribbons (x = 0–0.6) spun at a high wheel speed of 40 m/s crystallize in the TbCu7-type structure. The x-ray diffraction results analyzed by the Rietveld refinement method show that Ge prefers to occupy the 2e sites in the TbCu7-type structure. The grain size of the ribbons is only slightly decreased with the proper amount of Ge substitution (x < 0.7). When increasing x from 0–0.6, the coercivity of the SmCo7–xGex ribbons is enhanced from 1.9 kOe for binary SmCo7 to 7.5 kOe for SmCo6.5Ge0.5 which is mainly due to the enhancement of the magnetic anisotropy field by the Ge substitution for Co in 2e sites. Furthermore, a slight addition of carbon in the alloy is effective in refining the grain size and further improving the coercivity of the ribbons. Coercivity as high as 11.4 kOe could be obtained for SmCo6.7Ge0.3C0.1 ribbons.