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TT: Fachverband Tiefe Temperaturen

TT 49: Frustrated Magnets: Strong Spin-Orbit Coupling I

TT 49.8: Vortrag

Mittwoch, 20. März 2024, 17:00–17:15, H 2053

Rotational disorder in the triangular spin-liquid candidate Na₂BaCo(PO₄)₂ — Vera P. Bader¹, Ivo Heinmaa², Raivo Stern², Felix Schilberth³, Joachim Deisenhofer³, Istvan Kézsmárki³, Philipp Gegenwart¹, and •Alexander A. Tsirlin^1,4 — ¹EP VI, EKM, University of Augsburg, Germany — ²NICPB, Tallinn, Estonia — ³EP V, EKM, University of Augsburg, Germany — ⁴Felix Bloch Institute, Leipzig University, Germany

Using high-resolution x-ray diffraction, nuclear magnetic resonance, and infrared spectroscopy, we resolve the previously overlooked ferro-rotational distortion in the spin-1/2 triangular antiferromagnet Na₂BaCo(PO₄)₂. Cooperative rotations of the CoO₆ octahedra reduce the symmetry to P3 while leading to only minor changes in the spin Hamiltonian. The rotations are accompanied by Na displacements that indicate an inherent structural randomness, which is present even at low temperatures and increases on heating. Our ab initio molecular dynamics simulations suggest that Na disorder is intimately linked to the cooperative rotations. We propose two mechanisms that may lead to the suppression of magnetic order in Na₂BaCo(PO₄)₂ due to structural randomness and elucidate the unusually low Néel temperature (T_N/J≃ 0.1) of this material. Our results suggest the importance of lattice degrees of freedom and hidden randomness for the physics of spin-liquid candidates.

Keywords: spin liquid; triangular antiferromagnet; disorder effects; Co-based frustrated magnet