Dresden 2020 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 35: Frustrated Magnets - Strong Spin-Orbit Coupling 1 (joint session TT/MA)

TT 35.8: Talk

Wednesday, March 18, 2020, 11:45–12:00, HSZ 304

Magnetic properties of two sodium ruthenates Na₂RuO₃ and Na₃RuO₄ — •Vera P. Bader¹, Alexander A. Tsirlin¹, Anton Jesche¹, Clemens Ritter², and Philipp Gegenwart¹ — ¹Center for Electronic Correlations and Magnetism, University of Augsburg, Augsburg, Germany — ²Institut Laue-Langevin, Grenoble, France

Ruthenates show a diversity of magnetic phenomena, e.g. due to transitions between the non-magnetic J = 0 state and excited J = 1 levels in Ru⁴⁺ [1] or due to strong Ru-O covalency in the case of Ru⁵⁺ [2]. Powder samples of Na₂RuO₃ and Na₃RuO₄ were prepared via solid state reactions in a controlled atmosphere. The Ru⁴⁺ ions in Na₂RuO₃ form honeycomb layers which are stacked along the crystallographic c-axis. The measured diffraction pattern could be simulated under the assumption of stacking faults. The inverse susceptibility deviates from the Curie-Weiss behaviour and shows a downward bending in the high temperature region indicating a paramagnetic Van Vleck contribution which would be expected for a J = 0 ground state. In Na₃RuO₄ the Ru⁵⁺ ions form isolated tetramers which are composed of two equilateral triangles. The magnetic susceptibility reveals an antiferromagnetic transition at 30 K while the heat capacity data show two successive phase transitions at 25 K and 28 K. Up to now, the origin of the two phase transitions is not known. Neutron diffraction reveals the absence of symmetry lowering upon both transitions and the development of incommensurate magnetic order.

[1] J. Chaloupka et al., arXiv:1910.00074 (2019)

[2] A. Hariki et al., PRB 96 155135 (2017)