Universal fluctuating regime in triangular chromate antiferromagnets

Triangular antiferromagnets serve as a promising platform for creating novel spin-liquid states characterized by non-local entanglement and fractionalized excitations[1]. Herein, we report x-ray diffraction, magnetic susceptibility, heat capacity, 1H nuclear magnetic resonance (NMR), and muon spin relaxation (µSR) measurements, as well as density-functional band-structure calculations for the frustrated S = 3/2 triangular lattice Heisenberg antiferromagnet (TLHAF) α-HCrO2 (trigonal, space group: R-3m). This compound undergoes a clear magnetic transition at TN = 22.5 K, as seen from the drop in the muon paramagnetic fraction and concurrent anomalies in the magnetic susceptibility and specific heat. Local probes (NMR and µSR) reveal a broad regime with slow fluctuations down to 0.7 TN, this temperature corresponding to the maximum in the µSR relaxation rate and in the NMR wipe-out[2]. From the comparison with NaCrO2 and α -KCrO2, the fluctuating regime and slow dynamics below TN appear to be hallmarks of the TLHAF with ABC stacking that leads to a frustration of interlayer couplings between the triangular planes[3]. This interlayer frustration is a powerful lever to generate spin states with persistent dynamics and may bear implications to spin-liquid candidates with the triangular geometry.

[1] Y. Li, P. Gegenwart, and A. A. Tsirlin, Spin liquids in geometrically perfect triangular antiferromagnets, J. Phys.:Condens. Matter 32, 224004 (2020).
[2] A. Olariu, P. Mendels, F. Bert, B. G. Ueland, P. Schiffer, R. F. Berger, and R. J. Cava, Unconventional Dynamics in Triangular Heisenberg Antiferromagnet NaCrO2, Phys. Rev. Lett. 97, 167203 (2006).
[3] D. Hsieh, D. Qian, R. F. Berger, C. Liu, B. Ueland, P. Schiffer, Q. Huang, R. J. Cava, J. W. Lynn, and M. Hasan, Spin order by quantum frustration in triangular lattice Mott insulator NaCrO2: A neutron scattering study, arXiv:1405.6184.

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