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| Talk (non-conference) (Invited) | FZJ-2025-02152 |
2025
Abstract: Resolving crystal and magnetic structures using diffraction methods is of indispensable importance, as it serves as the key towards understanding the properties of functional material in a broad sense. In this talk, I would like to give a brief introduction to my previous research done using X-ray and neutron diffraction focusing on three case studies:1. The first object is kagome superconductor LaRu3Si2, which besides superconductivity below ca. 7K features a cascade of structural phase transitions with temperature [1]. Using variable-temperature X-ray diffraction I show which superstructure orders evolve in this material. Furthermore, using (3+N)D crystallography approaches, the models of crystal structures in direct space were proposed.2. The interplay between band topology and magnetism can result in intricate physics. Here I would like to present the results of the microscopic magnetic studies using neutron powder diffraction for the LnSbTe (Ln – lanthanides) family of Dirac nodal line semimetals. Although bulk properties measurements hint at single antiferromagnetic transition in HoSbTe and TbSbTe, neutron powder diffraction measurements reveal multiple incommensurate and commensurate phases coexisting or competing in below the Neel temperature [2]. Magnetic symmetry arguments suggest multi-k order in one member, TbSbTe. The possible relation of this peculiar magnetic behavior with the electronic structure is outlined.3. Layered nickelates were re-discovered recently as high-temperature superconductors at elevated pressure. Similar to cuprates and iron-based families, the superconductivity, structural and magnetic instabilities represent competing phenomena and can be tuned by external (pressure) or internal (substitution) parameters. In the case of the prototype member, La3Ni2O7, spin density wave order has been deduced using various macroscopic and microscopic probes. Still the most direct method – neutron diffraction – was ineffective in detecting this magnetic order, raising debates on the nature of the magnetically ordered state in this material. Using high-flux cold neutron diffraction, I unambiguously show long-range character of the spin-density wave in the oxygen stoichiometric La3Ni2O7 and La2PrNi2O7. The magnetic structure represents alternating Ni-moment stripes of 0.8µB and 0.15µB. The proposed models reproduce also the features of muon spectra. One peculiar feature of La3Ni2O7 is the presence of several magnetic stacking polymorphs.[1] Plokhikh, I., Mielke III, C., Nakamura, H., et al. (2024). Discovery of charge order above room-temperature in the prototypical kagome superconductor La(Ru₁₋ₓFeₓ)₃Si₂. Communications Physics, 7, 182.[2] Plokhikh, I., Pomjakushin, V., Gawryluk, D. J., Zaharko, O., & Pomjakushina, E. (2022). Competing magnetic phases in LnSbTe (Ln = Ho and Tb). Inorganic Chemistry, 61(29), 11399–11409.[3] Plokhikh, I., Hicken, T. J., Keller, L., et al (2025). Unraveling spin density wave order in layered nickelates La₃Ni₂O₇ and La₂PrNi₂O₇ via neutron diffraction (arXiv:2503.05287).
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