From magnetic order to spin-liquid ground states on the S= 32 triangular lattice

The series of compounds AAg2Cr[VO4]2, with A=Ag, K, or Rb, is layered S = 3/2 triangular-lattice (TL) systems in which the magnetic exchange interactions between Cr3+(3d3) ions are mediated by nonmagnetic [VO4]3- entities. Here, the relative orientation of the vanadate is altered with respect to the TL as a function of the A site, which corresponds to an induced symmetry change of the [CrO6] complex. All members of this series of compounds belong to the class of frustrated TL antiferromagnets. We find that the distorted TL (A=Ag) exhibits collinear antiferromagnetic long-range order (LRO) at TN≈10 K, whereas the high-symmetry cases (A=K, Rb) evade LRO in zero field down to 0.03 K, the lowest temperature of our experiments. The latter members of the series belong to the undistorted TL and are candidates for spin-liquid ground states presumably not related to Ising anisotropy or dimerization.