Understanding Spin Textures in Frustrated Magnets*

Magnetic frustration can suppress conventional magnetic ordering and stabilize unconventional magnetic states. These states can include spin liquids, in which conventional long-range magnetic order is absent. Alternatively, frustration may promote complex long-range magnetic order with novel properties. For example, materials with noncoplanar magnetic structures can show unusual physical properties driven by their nontrivial topology [1]. In this talk, I will discuss how neutron-scattering experiments can be used to determine spin textures in frustrated magnets, and to identify the magnetic interactions that stabilize them. I will focus on two classes of magnetic materials. First, I show that the insulating double perovskites Ba₂YRuO₆ and Ba₂LuRuO₆ [2] host a noncoplanar triple-q structure on the face-centred cubic lattice. By refining the magnetic structure and magnetic interactions simultaneously against inelastic neutron-scattering data, we show that this triple-q structure is stabilized by biquadratic interactions [3]. Second, I discuss centrosymmetric magnets containing Gd³⁺ ions, such as Gd₂PdSi₃ and GdRu₂Si₂, which host multi-q skyrmion spin textures under small applied magnetic fields [4,5]. I show how magnetic diffuse scattering measured above the magnetic ordering temperature can identify the magnetic interactions that stabilize the skyrmion phase, establishing a space of magnetic interactions that can promote skyrmion formation [6]. I conclude by discussing the outlook for refinement of magnetic models in interaction space, and introduce a computer program that can be used to refine interaction models against magnetic diffuse-scattering data [7].

[1] Tokura & Kanazawa, Chem. Rev. 121, 2857 (2021); [2] Battle & Jones, J. Solid State Chem. 78, 108 (1989); [3] Paddison et al., arXiv 2301.11395 (2023); [4] Kurumaji et al., Science 365, 914 (2019); [5] Khanh et al., Nat. Nanotechnol. 15, 444 (2020); [6] Paddison et al., Phys. Rev. Lett. 129, 137202 (2022); [7] Paddison, J. Phys.: Condens. Matter 35, 495802 (2023).