Effects of Hf and CNTs on structure and magnetic properties of TbCu 7-type Sm–Co magnets

Abstract

SmCo 7, SmCo 6.9Hf 0.1, SmCo 6.9Hf 0.1(CNTs) 0.05 and SmCo 6.9Hf 0.1(CNTs) 0.1 as-cast alloys and ribbons melt-spun at the speed of 40 m/s are prepared. The X-ray diffractometer, electron microscope and magnetometer are employed to investigate the effects of Hf and CNTs on structure and magnetic properties of the as-cast alloys and ribbons. The results show that Hf and CNTs additions in SmCo 7 alloys can stabilize TbCu 7 structure. Hf addition can form HfCo 2 grain boundary phase. Fine dispersed Hf(CNTs) grain boundary phase can be derived from simultaneous addition of Hf and CNTs. The four types of ribbons all consist of TbCu 7-type Sm(Co,Hf) 7 main phase. Cooling rate is the key factor of forming TbCu 7-type phase. It is attempted that the grain boundaries with CNTs addition mainly consist of Sm(Co,Hf) 7(CNTs) x . The coercivity, remanence and remanence ratio of the ribbons all increase with Hf and CNTs additions. The comprehensive magnetic properties of SmCo 6.9Hf 0.1(CNTs) 0.05 ribbons are H ci = 13.95 kOe, M r = 48.85 emu/g, M 2T = 61.09 emu/g and M r/M 2T = 0.80. Excessive CNT addition may worsen the magnetic properties.