Origin of spiral-spin order:picture NNN anisotropic AFM interactions:J262 a (b)Mn3 Mn 3 2 An approach without counting the DM interaction. S6 ↓↑ Dong et al.PRB78,155121(2008) Dong et al. PRB78, 155121 (2008)  NNN anisotropic AFM interactions: J2b>J2a. An approach without counting the DM interaction. Origin of spiral-spin order: picture