Mixed system Cs3Cu3Cl8-xBrxOH with weakly connected Cu-triangles

To study the relationship between the properties of low-dimensional spin systems with weakly coupled Cu-triangles and their crystal structure, single crystals of Cs3Cu3Cl8OH (1) and the new Cs3Cu3Cl7.6Br0.4OH (2) were grown. Both compounds are isostructural and crystallize in a monoclinic structure with space group P21/c. The magnetic susceptibility of (1) shows a maximum at 2.23 K and of (2) at 2.70 K, which are attributed to antiferromagnetic phase transitions. Furthermore, the magnetization along the b-axis at 1.9 K for both compounds shows a spin-flop transition into a new antiferromagnetic phase. This transition occurs at 0.61 T for (1) and at 2.0 T for (2). The antiferromagnetic order can be suppressed by a magnetic field BC1 = 1.1 T for (1) and BC2 = 1.2 T for (2). First single crystal neutron diffraction measured on (1) at different temperatures reveals the magnetic signal on the top of the nuclear reflection at (−1 0 0). Its magnetic ordering temperature was found to be at TN1 = 2.12(3) K.