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 245kAm−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 1270kAm−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.