Effects of Mn addition on the structures, magnetic properties and phase transformation of SmCo6.7−xMnxCr0.3 magnets

The effects of Mn addition on the structures, magnetic properties and phase transformation of mechanically alloyed SmCo6.7−xMnxCr0.3 (x = 0-0.6) magnets have been studied systematically. The results show that a small amount of Mn addition facilitates the formation of Th2Zn17-type 2:17 phase and significantly improves the intrinsic coercivities and the maximum energy products of the SmCo6.7−xMnxCr0.3 alloys. The phase transformation from Th2Ni17-type to Th2Zn17-type structure is observed in annealing the alloys. More Mn addition leads to the enhancement of the critical annealing temperature above which the magnetically soft Co phase appears, leading to an improvement in thermal stability of the magnetically hard 2:17 phase. The highest iHc of 17.2 kOe and the largest (BH)max of 7.1 MGOe are achieved for the SmCo6.1Mn0.6Cr0.3 alloy annealed at 800 °C for 30 min.