Regensburg 2022 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 8: Frustrated Magnets – Strong Spin-Orbit Coupling

TT 8.5: Talk

Monday, September 5, 2022, 18:15–18:30, H10

High-field ESR studies of the cubic Iridium hexahalide compounds (NH₄)₂IrCl₆ and K₂IrCl₆ — •Lakshmi Bhaskaran¹, Alexey N. Ponomaryov², Jochen Wosnitza^1,3, Nazir Khan⁴, Alexander A. Tsirlin⁴, Mike E. Zhitomirsky⁵, and Sergei A. Zvyagin¹ — ¹Dresden High Magnetic Field Laboratory (HLD-EMFL) and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany — ²Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany — ³Institut für Festkörper- und Materialphysik, TU Dresden, Dresden, Germany — ⁴University of Augsburg, Augsburg, Germany — ⁵University Grenoble Alpes, Grenoble, France

We report on high-field electron spin resonance studies of two iridium hexahalide compounds, (NH₄)₂IrCl₆ and K₂IrCl₆ [1]. In the paramagnetic state, our measurements reveal isotropic g-factors g = 1.79(1) for the Ir⁴⁺ ions, in agreement with their cubic symmetries. Most importantly, in the magnetically ordered state, we observe two magnon modes with zero-field gaps of 11.3 and 14.2 K for (NH₄)₂IrCl₆ and K₂IrCl₆, respectively. Based on that and using linear spin-wave theory, we estimate the nearest-neighbor exchange couplings and anisotropic Kitaev interactions, J₁/k_B=10.3 K, K/k_B=0.7 K for (NH₄)₂IrCl₆, and J₁/k_B=13.8 K, K/k_B=0.9 K for K₂IrCl₆, revealing the nearest-neighbor Heisenberg coupling as the leading interaction term, with only a weak Kitaev anisotropy.
[1] L. Bhaskaran et al., Phys. Rev. B 104, 184404 (2021).