Microstructure and coercivity of nitrided Mn–Sn-based alloys

• We investigated the microstructure of MnSn(Co)N alloys with high coercivity.
• Some twins and stacking faults were observed in the MnSnN alloy.
• The maximum coercivity of MnSnCoN alloy reached to 1270 kAm-1.
• The coercivity of the MnSnCoN alloy is indicated as pinning of domain wall type.
• In the MnSnCoN alloy, there were many twins in perovskite-type phases.

The microstructure of Mn–Sn–N and Mn–Sn–Co–N alloys was investigated by scanning electron microscopy and transmission electron microscopy (TEM). After the Mn–Sn alloy was annealed at 1000 °C under nitrogen, the coercivity increased to 245 kA m−1 and a lamellar structure appeared. The TEM images showed that the lamellar structure contained twins in the perovskite-type phase. After the Mn–Sn–Co alloy was annealed at 900 °C and subsequently annealed at 500 °C under nitrogen, the coercivity increased dramatically to 1270 kA m−1. A fine two-phase structure consisting of β-Mn and perovskite-type phases was observed, and some twins were present in the perovskite-type phases. In addition, a higher twin density was observed in the Mn–Sn–Co–N alloy than in the Mn–Sn–N alloy. These results indicate that the twins increased the coercivity of nitrided Mn–Sn based alloys.