Characterization of the spin-½ 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 themagnetic susceptibility, heat capacity, electron paramagnetic resonance, and Raman spectroscopy were performed. Our experiments conclusively show that a ferromagnetic Transition occurs at ∼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 Jnn-Jnnn 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