Journal article

Two-dimensional tetramer-cuprate Na5RbCu4(AsO4)4Cl2: phase transitions and AFM order as seen by 87Rb NMR

We report the 87Rb NMR results in a recently synthesized Na5RbCu4(AsO4)Cl2. This complex novel two-dimensional (2D) cuprate is an unique magnetic material, which contains layers of coupled Cu4O4 tetramers. In zero applied magnetic field, it orders antiferromagnetically via a second-order low-entropy phase transition at TN = 15 (1) K . We characterize the ordered state by 87Rb NMR, and suggest for it a non-collinear rather than collinear arrangement of spins. We discuss the properties of Rb nuclear site and point out the new structural phase transition(s) around 74 and 110 K.


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