Frustrated spin chain physics near the Majumdar-Ghosh point in szenicsite Cu$_3$(MoO$_4$)(OH)$_4$

TL;DR

This study combines experimental and theoretical methods to investigate the magnetic properties of szenicsite, revealing its central chain as a frustrated $J_1$-$J_2$ antiferromagnetic spin chain near the Majumdar-Ghosh point, with nearly decoupled side chains.

Contribution

It provides the first detailed characterization of szenicsite's magnetic behavior, identifying the central chain as a frustrated $J_1$-$J_2$ model close to the Majumdar-Ghosh point.

Findings

Central chain described by frustrated $J_1$-$J_2$ model with $J_1 \\simeq 68$ K.

Side chains are antiferromagnetic dimers with couplings >200 K.

Heat capacity indicates proximity to the Majumdar-Ghosh point.

Abstract

In this joint experimental and theoretical work magnetic properties of the Cu$^{2+}$ mineral szenicsite Cu$_3$(MoO$_4$)(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 CuO$_4$ plaquettes, while the two side chains feature a corner-sharing zig-zag 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 $J_1\simeq 68$ 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 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, $J_2/J_1=0.5$.