Magnetic properties of the low-dimensional spin-1/2 magnet \alpha-Cu_2As_2O_7

TL;DR

This study investigates the magnetic behavior of the low-dimensional spin-1/2 magnet lpha-Cu_2As_2O_7, revealing a quasi-one-dimensional Heisenberg chain structure with complex magnetic interactions and quantum fluctuations.

Contribution

It combines experimental measurements with DFT and QMC simulations to elucidate the magnetic structure and interactions in lpha-Cu_2As_2O_7, highlighting its quasi-1D nature and quantum effects.

Findings

Identification of quasi-1D coupled alternating spin-1/2 Heisenberg chains.

Observation of antiferromagnetic order at T_N 9 10K.

Detection of a spin-flop transition at B_{SF} 9 1.7T.

Abstract

In this work we study the interplay between the crystal structure and magnetism of the pyroarsenate \alpha-Cu_2As_2O_7 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 non-magnetic AsO_4 tetrahedra. Owing to residual 3D interactions antiferromagnetic long range ordering at T_N\simeq10K takes place. Application of external magnetic field B along the magnetically easy axis induces the transition to a spin-flop phase at B_{SF}~1.7T (2K). 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=164K, the weaker intrachain coupling J'_1/J_1 = 0.55, and the effective interchain coupling J_{ic1}/J_1 = 0.20.