Effect of Cu substitution on structure and magnetic properties of anisotropic SmCo ribbons

Anisotropic SmCo7-xCux (x=0-4.5) ribbons have been prepared by melt spinning at a low wheel speed of 5 m/s. Scanning electron microscopy results show that Cu-free and Cu-containing ribbons consist of equiaxed and columnar dendrite grains, respectively. The arrangement of columnar dendrite grains of the ribbons was found to be more ordered with increasing Cu content x. Together with the results of magnetic measurement, it is derived that Cu substitution is helpful to enhance the degree of preferred orientation of the c-axis of the columnar dendrite grains parallel to the longitudinal direction of the ribbons. In this way the rectangularity of demagnetization curves and the remanence ratio (defined as the ratio of remanent magnetization to saturation magnetization) of the samples are significantly improved. A remanence ratio of 0.90, which is close to that of sintered SmCo magnets, has been achieved in the ribbons with x=2.5. Because the domain-wall-energy gradient between the 1:5 and 2:17 phases, which determines the value of the coercive force arising from the domain wall pinning, may increase with x, the coercivity of the samples with x≤3.5 increases strongly with x. Without heat treatment, a coercive force (iHc) of up to 9.2 kOe is obtained in the ribbons with x=3.5