Noncoplanar Spin Textures in Cubic Double Perovskites Ba₂YRuO₆ and Ba₂LuRuO₆

Magnetic materials with noncoplanar magnetic structures can show unusual physical properties driven by nontrivial topology. Topologically-active states are often multi-q structures, which are challenging to stabilize in models and to identify in materials. In this talk, we use inelastic neutron-scattering data to show that the insulating double perovskites Ba₂YRuO₆ and Ba₂LuRuO₆ -- previously assumed to be collinear antiferromagnets -- actually host a noncoplanar triple-q structure on the face-centered cubic lattice. I discuss the magnetic interactions that may stabilize this state, considering biquadratic exchange and cubic anisotropy. Our work identifies cubic double perovskites as a promising class of materials to realize topological magnetic states, elucidates the likely stabilization mechanism of the triple-q state in these materials, and establishes neutron spectroscopy on powder samples as a valuable technique to distinguish multi-q from single-q structures, facilitating the discovery of topologically-nontrivial magnetic materials.