paper

Magnetic structure and Dzyaloshinskii-Moriya interaction in the $S = 1/2$ helical-honeycomb antiferromagnet $I^\pm$ -Cu $_{2}$ V $_{2}$ O $_{7}$

arXiv:1502.02769 · doi:10.1103/PhysRevB.92.024423

Abstract

Magnetic properties of the $S = 1/2$ antiferromagnet $I^\pm$ -Cu $_{2}$ V $_{2}$ O $_{7}$ have been studied using magnetization, Quantum Monte Carlo (QMC) simulations, and neutron diffraction. Magnetic susceptibility shows a broad peak at $\sim 50$ ~K followed by an abrupt increase indicative of a phase transition to a magnetically ordered state at $T_{N}$ = 33.4(1) K. Above $T_{N}$ , a fit to the Curie-Weiss law gives a Curie-Weiss temperature of $I^ = - 73 (1)$ ~K suggesting the dominant antiferromagnetic coupling. The result of the QMC calculations on the helical-honeycomb spin network with two antiferromagnetic exchange interactions $J_{1}$ and $J_{2}$ provides a better fit to the susceptibility than the previously proposed spin-chain model. Two sets of the coupling parameters $J_{1} : J_{2} = 1 : 0.45$ with $J_{1} = 5.79 (1)$ ~meV and $0.65 : 1$ with $J_{2} = 6.31 (1)$ ~meV yield equally good fits down to $\sim T_{N}$ . Below $T_{N}$ , weak ferromagnetism due to spin canting is observed. The canting is caused by the Dzyaloshinskii-Moriya interaction with an estimated $b c$ -plane component $∣ D_{p} ∣$ $≃ 0.14 J_{1}$ . Neutron diffraction reveals that the $S = 1/2$ Cu $^{2 +}$ spins antiferromagnetically align in the $F d^{'} d^{'} 2$ magnetic space group. The ordered moment of 0.93(9)~ $I^¼_{B}$ is predominantly along the crystallographic $a$ -axis.

11 pages, 9 figures

Magnetic structure and Dzyaloshinskii-Moriya interaction in the S=1/2 helical-honeycomb antiferromagnet I^±-Cu2​V2​O7​

Abstract

Magnetic structure and Dzyaloshinskii-Moriya interaction in the $S = 1/2$ helical-honeycomb antiferromagnet $I^\pm$ -Cu $_{2}$ V $_{2}$ O $_{7}$