Origin of spiral-spin order:back to origin 3D lattice simulation(CT=3D canted spin phase) 175 (a) E λQ2l=1.5 150 CT 125 100.0 100 A Tb 75 D Tb No JT 50 J2-52 10 20 3040 500 10 20304050010203040 50 J,(0.001)  3D lattice simulation (CT=3D canted spin phase) No JT J2b=J2a J2b=J2a J2a=0 Origin of spiral-spin order: back to origin