Magneto-structural properties of the layered quasi-2D triangular-lattice antiferromagnets Cs2CuCl4-xBrx for x = 0,1,2 and 4
Abstract
We present a study of the magnetic susceptibility mol under variable hydrostatic pressure on single crystals of Cs2CuCl4-xBrx. This includes the border compounds x = 0 and 4, known as good realizations of the distorted triangular-lattice spin-1/2 Heisenberg antiferromagnet, as well as the isostructural stoichiometric systems Cs2CuCl3Br1 and Cs2CuCl2Br2. For the determination of the exchange coupling constants J and J, mol data were fitted by a J-J model Schmidt2015. Its application, validated for the border compounds, yields a degree of frustration J/J = 0.47 for Cs2CuCl3Br1 and J/J 0.63 - 0.78 for Cs2CuCl2Br2, making these systems particular interesting representatives of this family. From the evolution of the magnetic susceptibility under pressure up to about 0.4\,GPa, the maximum pressure applied, two observations were made for all the compounds investigated here. First, we find that the overall energy scale, given by Jc = (J2 + J 2)1/2, increases under pressure, whereas the ratio J/J remains unchanged in this pressure range. These experimental observations are in accordance with the results of DFT calculations performed for these materials. Secondly, for the magnetoelastic coupling constants, extraordinarily small values are obtained. We assign these observations to a structural peculiarity of this class of materials.