, Volume 170, Issue 5-6, pp 236-241

Pulsed-Field Ultrasonic Experiments in the Quasi-2D Antiferromagnet Cs2CuBr4

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Abstract

The magnetic insulators Cs2CuCl4 and Cs2CuBr4 are model systems for a frustrated quasi-two-dimensional triangular-lattice spin-1/2 Heisenberg antiferromagnet with a weak interlayer coupling. The quasi-two-dimensional character manifests itself in a broad maximum at T max in the magnetic susceptibility, which for Cs2CuCl4 has been found to mark the upper bound for a spin-liquid regime (R. Coldea et al. in Phys. Rev. B 68:134424, 2003). Motivated by the observation of characteristic B 2 dependencies in the elastic constants and ultrasound attenuation in the spin-liquid regime for this material, we look for corresponding signatures in the related Cs2CuBr4 compound at low temperatures T≤4.2 K and fields B≤50 T. We observe a softening of the elastic constant up to B s ∼32 T (Ba) and a maximum in the sound attenuation at 0.86 B s . Both quantities exhibit the same characteristic B 2 dependence as found for Cs2CuCl4, suggesting the existence of a spin-liquid phase in Cs2CuBr4 as well.