Structure and magnetic properties of SmCo7−xGax (0 ⩽ x ⩽ 1.2) alloys

• Effects of Ga addition on structure and magnetic properties of SmCo7 alloy were studied.
• A stable TbCu7-type single phase can be obtained in as-cast SmCo6.1Ga0.9 alloys.
• Ga addition affects the stability, order degree and nucleation of 1:7H phase.
• TbCu7-type phase in the ribbons is basically stable below 500 °C.
• The phase transition of ribbons during the heating process was discussed.

In this article, the effects of Ga addition on the structure and magnetic properties of SmCo7 alloy were studied. The results show that a stable TbCu7-type single phase can be obtained in as-cast SmCo7−xGax alloys when a proper amount of Ga is introduced (x = 0.9). Meanwhile, all SmCo7−xGax ribbons melt-spun at 40 m/s are composed of single TbCu7-type phase. So both the appropriate doping of Ga, and more especially the rapid cooling rate, can effectively stabilize the TbCu7-type structure. Moreover, Ga addition affects not only the stability and the order degree of 1:7H phase but also the uniformity of nucleation. Magnetic tests reveal that the coercivity, remanence and remanence ratio of the ribbons increase with the Ga addition, and reach their maximum values (7117.0 ± 2081.5 Oe, 36.7 ± 4.2 emu/g and 0.771 ± 0.037, respectively) when x = 0.9. At the same time, the maximum magnetization of ribbons and Curie temperature (Tc) of Sm–Co phases tend to decrease with the amount of Ga. In particular, the TbCu7-type phase in SmCo7−xGax ribbons is basically stable below 500 °C, and the phase transition during the heating process is also discussed.