Fig. 6: Magnetic-field dependence of the magnetic structure.

a Schematic figure of the magnetic structure of the broken helix state. The red arrows on the gray circles denote the magnetic moments lying on the helical plane at the Eu sites, while the green triangles are As sites beside the Eu layers. The dotted arrows represent the rotation of the magnetic moment from the direction of the magnetic moment in the lower layer. b–e Schematic illustrations of incommensurate magnetic structures viewed along the c-axis, which are evolved by the in-plane magnetic field (\({{\bf{B}}}_{{\rm{ext}}}\parallel [1\bar{1}0]\)) from a broken helix (BH, b) to a semi-circle fan (S-Fan, c), a fan (Fan, d), and a forced ferromagnetic (FM, e) state. The density of the red arrows and gray gradations represent the distribution of the ordered magnetic moments in the broken helix, semi-circle fan, and fan state.