Origin of spiral-spin order:back to origin DE+SE+NNN anisotropic AFM interactions:J22 FqM2 150 0.25 (c) (a) 125 90.2 0.15 100.00 100 0.1 75 0.05 50 Spiral 15 120 25 A 0 60 JAF(0.001)30 80 100 60 0 20 4060 80 100 。 20 40 J20.001) J2(0.001) (1)small wave-number,(2)phase SSO is coming out! transitions,(3)no energy gap Dong et al.PRB78,155121(2008) DE+SE+NNN anisotropic AFM interactions: J2b>J2a. SSO is coming out! (1) small wave-number, (2) phase transitions, (3) no energy gap q=qMn/2 Dong et al. PRB78, 155121 (2008) Origin of spiral-spin order: back to origin