Speaker
Description
In noncentrosymmetric magnetic materials, various types of nontrivial magnetic structures are realized as a result of competing interactions of symmetric magnetic exchange interaction, Dzyaloshinskii-Moriya type antisymmetric exchange interaction, and Zeeman energy in external magnetic fields, especially in Gd and Eu compounds with weak crystal field anisotropy. In many cases, they are non-collinear or non-coplanar structures associated with incommensurate spiral ordering. In this talk, we focus on the tetragonal EuTGe3 family without an inversion center but with mirror planes including the c-axis (space group I4mm). From our recent studies on EuIrGe3, EuNiGe3, and EuRhGe3, using circularly polarized resonant X-ray diffraction to investigate magnetic helicities, it was clarified that each compound exhibits distinctive ordering phenomena reflecting competing interactions. In EuIrGe3, successive transitions take place from sinusoidal (m || c) to cycloidal (m || ac or bc) structures with a tiny reorientation of the propagation vector from q=(0, 0, 0.792) to (0.017, 0, 0.792). Each of the four cycloidal domains has its own helicity. In EuNiGe3, single-q helical ordering at zero field with q=(0.26, 0.053, 0) transforms into a triple-q distorted triangular skyrmion lattice state in a magnetic field. Surprisingly, the original helicity at zero field is reversed to form a skyrmion lattice with unified helicity. In EuRhGe3, in contrast, the helical order propagating along the c-axis is free from the antisymmetric interaction.
REFERENCES
1. T. Matsumura et al., J. Phys. Soc. Jpn. 91, 073703 (2022). (arXiv:2206.06596).
2. K. Kurauchi et al., J. Phys. Soc. Jpn. 92, 083701 (2023). (arXiv:2306.12669).
3. T. Matsumura et al., J. Phys. Soc. Jpn. 93, 074705 (2024). (Open Select).
