Thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co2MnX(XÂ =Â Si, Ge, Sn)(1Â 0Â 0) surface

► Stability, magnetism and half-metallicity of Co2Mn[Si, Ge, Sn](1 0 0) are studied. ► CoCo termination of Co2MnSn(1 0 0) is excluded from thermodynamic equilibrium region. ► Surface Co or Mn atomic magnetic moment is enhanced by compared with the bulk. ► The minority-spin gap in Co2MnSn(1 0 0) has been destroyed by the surface states.