Abstract
In this work, we study the interplay between the crystal structure and magnetism of the pyroarsenate alpha-Cu2As2O7 by means of magnetization, heat capacity, electron spin resonance, and nuclear magnetic resonance measurements as well as density functional theory (DFT) calculations and quantum Monte Carlo (QMC) simulations. The data reveal that the magnetic Cu-O chains in the crystal structure represent a realization of a quasi-one-dimensional (1D) coupled alternating spin-1/2 Heisenberg chain model with relevant pathways through nonmagnetic AsO4 tetrahedra. Owing to residual 3D interactions, antiferromagnetic long range ordering at T-N similar or equal to 10 K takes place. Application of the external magnetic field B along the magnetically easy axis induces the transition to a spin-flop phase at B-SF similar to 1.7 T (2 K). The experimental data suggest that substantial quantum spin fluctuations take place at low magnetic fields in the ordered state. DFT calculations confirm the quasi-one-dimensional nature of the spin lattice, with the leading coupling J(1) within the structural dimers. QMC fits to the magnetic susceptibility evaluate J(1) = 164 K, the weaker intrachain coupling J'(1)/J(1) = 0.55, and the effective interchain coupling J(ic1)/J(1) = 0.20.