Effects of Hf and CNTs on magnetic transformation and thermal stabilities of TbCu7-type Sm–Co matrix ribbon magnets

Abstract SmCo 7 , SmCo 6.9 Hf 0.1 , SmCo 6.9 Hf 0.1 (CNTs) 0.05 and SmCo 6.9 Hf 0.1 (CNTs) 0.1 melt-spun ribbons are prepared at a speed of 40 m/s. The phase structure, magnetic transformation and thermal stability of the ribbons are studied using thermal analysis, high temperature in-situ XRD and thermomagnetic analysis. The results show the Hf and CNTs (carbon nanotubes) additions have no influence on the formation of TbCu 7 -type structure. Nevertheless, Hf addition may cause large heat storage; CNTs addition can lead to crystal-boundary blocking effect. The M – T curves of SmCo 7 matrix ribbons can all be divided into seven stages. The 1:7H decomposition, CoC x precipitation and 1:5 phase decrease successively emerge when the temperature increases from room temperature to 1100 °C.