Field-Dependent Magnetic Ordering Dome and Quantum Spin Fluctuations in the Natural Mineral Henmilite, Ca2Cu(OH)4[B(OH)4]2

The ideal candidates for quantum fluctuations study are low-spin low-dimensional materials, such as spin ½ chains. Some theoretically predicted spin arrangements exist only in natural mineral specimens, such as the maple leaf lattice in spangolite or the spin ladder in henmilite. The latter one is magnetically ordering at 0.2 K, with a significant broad magnetic hump in specific heat stretching well above the order transition – indicative of the build-up of magnetic correlations. Unusually for an antiferromagnet, the application of field enhances transition temperature up to 3 T, beyond which decreases towards the quantum critical point. We plan to use muons as the most appropriate probe for studying both the ground-state and the spin dynamics in zero-field and applied fields in dilution temperatures, and HiFi spectrometer is the best choice for such a study.