Static and dynamic properties of the frustrated spin-1/2 depleted-kagome antiferromagnet Cu$_7$(TeO$_3$)$_2$(SO$_4$)$_2$(OH)$_6$

Abstract

The structural and magnetic properties of the two-dimensional spin-$1/2$ depleted-kagome compound Cu$_7$(TeO$_3$)$_2$(SO$_4$)$_2$(OH)$_6$ are investigated using x-ray diffraction, magnetization, heat capacity, and $^1$H Nuclear Magnetic Resonance (NMR) measurements. From the analysis of magnetic susceptibility, we found a large Curie-Weiss temperature [$\theta_{\rm CW} = -50(2)$ K] and the co-existence of antiferromagnetic and ferromagnetic interactions. The value of $\theta_{\rm CW}$ gives an estimate of the average nearest-neighbour antiferromagnetic interaction of $J/k_{\rm B} \simeq 66$ K. The NMR relaxation rates ($1/T_1$ and $1/T_2$) exhibit a peak, providing evidence for a magnetic long-range order at $T^*\simeq 4$ K which appears to be canted antiferromagnetic type. Heat capacity also features a broad maximum at $T^*$ that moves towards higher temperatures with increasing magnetic field, reflecting defect induced Schottky anomaly. The frustration parameter $f_r = \lvert \theta_{\rm CW} \lvert/{T^{*}}\simeq 12.5$ renders the compound a highly frustrated low-dimensional magnet.