Natalija van Well (University Bayreuth, Germany)

The Cs2CuCl4-xBrx mixed system is very rich in structural and magnetic phases, which can be separated by their tetrahedral/octahedral Cu2+ environment. For the tetrahedral one, neutron diffraction investigation of the magnetic phase diagram of Cs2CuCl4-xBrx provides detailed information about the influence of a specific Br concentration on the magnetic structure [1]. For the octahedral one, the compounds are typical quasi 2-D antiferromagnets. The realisation of the new tetragonal phase of Cs2CuCl4 is possible using specific crystal growth conditions at a temperature below 281K. For the structure investigation, synchrotron powder diffraction was used. The susceptibility measurements of it show similar magnetic behaviour like the tetragonal Cs2CuCl2.9Br1.1, Cs2CuCl2.5Br1.5 and Cs2CuCl2.2Br1.8 and present consistent results for typical quasi 2-D antiferromagnets [2].The structure analysis down to 4K for Cs2CuCl2.2Br1.8 shows no phase transition and the tetragonal symmetry I4/mmm, being the same at room temperature. However, the new neutron single crystal diffraction investigation presents a very small orthorhombic distortion (subgroup relationship). Several magnetic reflections corresponding to the propagation vector k = (0, 0, 0) are observed for this compound below the magnetic phase transition at TN = 11.3K confirming its antiferromagnetic nature.

[1] Natalija van Well et al., Annalen der Physik, 530,1800270 (2018)

[2] P.T. Cong et al., IEEE Transactions on Magnetics 50, 2700204 (2014)