Characterization of the Spin-1/2 Linear-Spin-Chain Ferromagnet CuAs$_{2}$O$_{4}$

We are investigating Cu$^{2+}$ ($S=$1/2) linear-spin-chains systems exhibiting low-dimensional magnetism. Linear-spin-chains are formed when CuX$_{6}$ (X$=$O,Cl,Br,...) Jahn-Teller distorted octahedra link together via their trans-edges. Most often, these spin-chains support ferromagnetic (FM) nearest-neighbor (NN) and antiferromagnetic (AFM) next-nearest-neighbor (NNN) spin-exchange interactions, sometimes leading to an incommensurate spin-spiral structures with multiferroic behavior. There exists a magnetic phase diagram which can predict the intra-chain behavior using a ratio of spin-exchange constants, $\alpha =$Jnn/Jnnn. A quantum critical point exists on a boundary at $\alpha =$- 4, small spin exchange perturbations on a system with an $\alpha $ ratio in the vicinity of this point may induce a pronounced response of the system. In this study, we report on CuAs$_{2}$O$_{4}$ mineral name trippkeite, featuring CuO$_{2}$ ribbon chains. Trippkeite is an exceptional spin-chain system because it shows long-range FM ordering and has an $\alpha$ ratio close to -4. Measurements of magnetic susceptibility, heat capacity, Raman spectroscopy, and electron paramagnetic resonance were performed. DFT calculations and TMRG simulations were also carried out.