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Abstract

In this joint experimental and theoretical work magnetic properties of the Cu2+ mineral szenicsite Cu-3(MoO4)(OH)(4) are investigated. This compound features isolated triple chains in its crystal structure, where the central chain involves an edge-sharing geometry of the CuO4 plaquettes, while the two side chains feature a corner-sharing zigzag geometry. The magnetism of the side chains can be described in terms of antiferromagnetic dimers with a coupling larger than 200 K. The central chain was found to be a realization of the frustrated antiferromagnetic J(1)-J(2) chain model with J(1) similar or equal to 68 K and a sizable second-neighbor coupling J(2). The central and side chains are nearly decoupled owing to interchain frustration. Therefore, the low-temperature behavior of szenicsite should be entirely determined by the physics of the central frustrated J(1)-J(2) chain. Our heat-capacity measurements reveal an accumulation of magnetic entropy at low temperatures and suggest a proximity of the system to the Majumdar-Ghosh point of the antiferromagnetic J(1)-J(2) spin chain, J(2)/J(1) = 0.5.