Characterization of the spin-1/2 linear-chain ferromagnet CuAs2O4

The magnetic and lattice properties of the S = 1/2 quantum-spin-chain ferromagnet CuAs2O4, mineral name trippkeite, were investigated. The crystal structure of CuAs2O4 is characterized by the presence of corrugated CuO2 ribbon chains. Measurements of the magnetic susceptibility, heat capacity, electron paramagnetic resonance, and Raman spectroscopy were performed. Our experiments conclusively show that a ferromagnetic transition occurs at similar to 7.4 K. Ab initio DFT calculations reveal dominant ferromagnetic nearest-neighbor and weaker antiferromagnetic next-nearest-neighbor spin exchange interactions along the ribbon chains. The ratio of J(nn)/J(nnn) is near -4, placing CuAs2O4 in close proximity to a quantum critical point in the J(nn)-J(nnn) phase diagram. TMRG simulations used to analyze the magnetic susceptibility confirm this ratio. Single-crystal magnetization measurements indicate that a magnetic anisotropy forces the Cu2+ spins to lie in an easy plane perpendicular to the c axis. An analysis of the field-and temperature-dependent magnetization by modified Arrott plots reveals a 3d-XY critical behavior. Lattice perturbations induced by quasihydrostatic pressure and temperature were mapped via magnetization and Raman spectroscopy.