Improving the structure, magnetic properties and thermal stability of rapidly quenched TbCu7-type SmCo6.4Si0.3Zr0.3 alloy by carbon addition

The effects of carbon addition on the structure and magnetic properties of rapidly quenched TbCu7-type SmCo6.4Si0.3Zr0.3 alloy have been investigated. The alloys with a small amount of C addition (x≤0.2) showed single Sm(Co,M)7 phase, while ZrC phase appeared in the alloys with x=0.3 and 0.4. With the increase of C content, the grain size decreased from approximately 850 nm for x=0.1 to approximately 300 nm for x=0.4. The coercivity Hc and maximum magnetic energy product (BH)max increased with the C content from x=0 to 0.2 and then decreased with excessive C addition. The optimal magnetic properties of Hc=1577 kA/m, Jr=0.53 T and (BH)max=52.1 kJ/m3 were achieved for SmCo6.4Si0.3Zr0.3C0.2 alloy with a grain size of 600–700 nm, which is close to the single domain size of TbCu7-type Sm(Co,Zr)7 alloy. Furthermore, C addition also improved the thermal stability by reducing the absolute values of temperature coefficients of remanence and coercivity.