Two energy scales of spin dimers in clinoclase Cu3(AsO4)(OH)3

Magnetic susceptibility and microscopic magnetic model of the mineral clinoclase Cu3(AsO4)(OH)3 are reported. This material can be well described as a combination of two nonequivalent spin dimers with the sizable magnetic couplings of J about 700 K and J(D2) about 300 K. Based on density functional theory calculations, we pinpoint the location of dimers in the crystal structure. Surprisingly, the largest coupling operates between the structural Cu2O6 dimers. We investigate magnetostructural correlations in Cu2O6 structural dimers, by considering the influence of the hydrogen position on the magnetic coupling. Additionally, we establish the hydrogen positions that were not known so far and analyze the pattern of hydrogen bonding.