Magnetic and magneto-elastic couplings in the low-dimensional Heisenberg quantum magnet Cs2CuCl2Br2 with octahedral Cu coordination

Abstract In single crystals of the solid solution Cs 2 CuCl 4 - x Br x ( 0 ⩽ x ⩽ 4 ), depending on the growth conditions, two structural modifications with a tetrahedral or an octahedral Cu environment can be realized. The border compounds (x = 0 and 4) with a tetrahedral Cu coordination have been recognized as model systems for quasi-2D frustrated anisotropic triangular quantum antiferromagnets. This holds true also for the newly discovered stoichiometric compounds with x = 1 and 2. In contrast, the systems exhibiting an octahedral Cu environment can be classified as quasi-2D ferromagnets characterized by ferromagnetic layers with a weak inter-layer coupling. Here we study the magnetic and magneto-elastic couplings for the low-dimensional Heisenberg quantum magnet Cs 2 CuCl 2 Br 2 with octahedral Cu coordination. By applying magnetic susceptibility measurements under varying hydrostatic (He-gas) pressure, χ ( T , p ) , we determine the pressure dependence of the magnetic coupling constant ∂ J / ∂ p and estimate the magneto-elastic couplings ∂ J / ∂ ∊ v . These values are enhanced by almost one order of magnitude compared to Cs 2 CuCl 2 Br 2 with tetrahedral Cu coordination.