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Magnetism of Cs2Cu3SnF12 kagome compound studied by NQR

Cs2Cu3SnF12 (CCSF) is a kagome sister compound of Rb2Cu3SnF12 (RCSF) in which the nearest neighbour spins form singlets in a valence bond solid structure that resembles a pinwheel. Although simple, the substitution of Rb by Cs drastically alters the ground state and a Néel state is formed in CCSF. It has been argued that such a significant ground state change is due to the increased Dzyaloshinskii-Moriya (DM) interaction [1]. Such a scenario has been theoretically predicted for an isotropic quantum kagome lattice, where the large DM interaction [2] drives the quantum critical point emerges from a non-magnetic state. We have studied the CCSF system by nuclear quadrupole resonance (NQR) of 63, 65Cu. Below the temperature of 187 K we observe a splitting of the NQR lines due to a structural transition (similar as the one in RCSF), while below TN=20.5 K the lines split further due to the onset of magnetism. We study the effects of the structural change and inspect its relation to the formation of the Néel state. From the known structure and the temperature dependence of the NMR/NQR perturbation we extract the temperature dependence of the order parameter. We also performed measurements under pressure to try to suppress the Néel state. We discuss our results in the view of existing models. [1] K. Katayama, N. Kurita and H. Tanaka, Phys. Rev. B 91, 214429 (2015). [2] O. Cépas , C. M. Fong, P. W. Leung, and C. Lhuillier, Phys. Rev. B 78, 140405(R) (2008).

NMR ; kagome ; frustration ; moment

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