Enhancement of coercivity for melt-spun SmCo7-xTax ribbons with Ta addition

The effect of Ta addition on the structure and magnetic properties of melt-spun SmCo7-xTax (x = 0-0.6) ribbons has been investigated. The intrinsic coercivity increases dramatically from 1.9 kOe for Ta-free ribbon to 9.8 kOe for SmCo6.7Ta0.3 ribbon, while further increasing Ta results in little enhancement of the coercivity. XRD patterns reveal that SmCo7-xTax ribbons crystallize in the pure TbCu7-type structure for low Ta substitution of x <= 0.3 and a minor phase of TaCo3 appears when x<0.3. According to Rietveld structure refinement, the ternary alloying element Ta prefers to occupy the 2e site of TbCu7-type structure. The mechanism of the coercivity enhancement has been discussed based on crystal structure and microstructure. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3334494]