Unconventional magnetic transitions in the mineral clinoatacamite Cu2Cl(OH)3 -: art. no. 052409

Unconventional magnetic properties are found for a quantum spin system of mineral clinoatacamite, Cu2Cl(OH)(3). Clinoatacamite is found to undergo an antiferromagnetic transition at 18.1 K with a small entropy fall (0.05R In 2). At temperatures below 6.4 K, it transits into a disordered spin-glass-like state but with large specific heat anomalies. The entire entropy fall for the spin system is about 0.31R In 2, which is smaller than those for dipolar spin ice (0.67R ln 2) and for ice I-h (0.71R ln 2). Geometric frustration for the quantum Cu2+ spins is suggested based on its crystal structure, magnetization, and specific heat studies.