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@INPROCEEDINGS{Plokhikh:1041118,
      author       = {Plokhikh, Igor},
      title        = {{D}iffraction studies of quantum materials},
      reportid     = {FZJ-2025-02152},
      year         = {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).},
      organization  = {(Digital) Institute Seminar JCNS-2,
                       (Germany)},
      subtyp        = {Invited},
      cin          = {JCNS-2 / JARA-FIT},
      cid          = {I:(DE-Juel1)JCNS-2-20110106 / $I:(DE-82)080009_20140620$},
      pnm          = {632 - Materials – Quantum, Complex and Functional
                      Materials (POF4-632) / 6G4 - Jülich Centre for Neutron
                      Research (JCNS) (FZJ) (POF4-6G4)},
      pid          = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G4},
      typ          = {PUB:(DE-HGF)31},
      url          = {https://juser.fz-juelich.de/record/1041118},
}