Abstract
The Ba3Cu3In4O12 stands for unique topology of the magnetic subsystem. It consists of rotated by 90 degrees relative to each other "paper-chain" columns made of vertex-sharing (CuO4)-O-I and (CuO4)-O-II planar units. The overall pattern of the copper ions is that of a three-dimensional Shastry-Sutherland network. At high temperatures, the magnetic susceptibility follows the Curie-Weiss law with positive Weiss temperature indicating strong predominance of ferromagnetic coupling. At low temperatures, however, this compound exhibits a long-range antiferromagnetically ordered state that reaches saturation magnetization by a nontrivial succession of two spin-flop and two spin-flip transitions already in modest magnetic fields. We show that the ground state in Ba3Cu3In4O12 may be a three-dimensional orthogonal arrangement of the Cu2+ (S = 1/2) magnetic moments forming three virtually independent antiferromagnetic subsystems. In this arrangement, favored by anisotropic exchange interactions, the quantum fluctuations provide the coupling between three mutually orthogonalmagnetic subsystems resulting in an impressive "order by disorder" effect.