Magnetic properties of the S=1/2 quasi square lattice antiferromagnet CuF2(H2O)2(pyz) (pyz=pyrazine) investigated by neutron scattering

TL;DR

This study investigates the magnetic structure and excitations of CuF2(H2O)2(pyz), revealing a collinear antiferromagnetic order with significant quantum fluctuations and a predominantly two-dimensional magnetic exchange interaction.

Contribution

First detailed neutron scattering analysis of the magnetic properties of CuF2(H2O)2(pyz), demonstrating quantum fluctuation effects and confirming a 2D Heisenberg model description.

Findings

Collinear antiferromagnetic structure with moments along [0.7 0 1]

Ordered magnetic moment of 0.60 μB, indicating strong quantum fluctuations

Spin wave dispersion consistent with a 2D Heisenberg model with J2d ≈ 0.934 meV

Abstract

We have performed elastic and inelastic neutron experiments on single crystal samples of the coordination polymer compound CuF2(H2O)2(pyz) (pyz=pyrazine) to study the magnetic structure and excitations. The elastic neutron diffraction measurements indicate a collinear antiferromagnetic structure with moments oriented along the [0.7 0 1] real-space direction and an ordered moment of 0.60 +/- 0.03 muB/Cu. This value is significantly smaller than the single ion magnetic moment, reflecting the presence of strong quantum fluctuations. The spin wave dispersion from magnetic zone center to the zone boundary points (0.5 1.5 0) and (0.5 0 1.5) can be described by a two dimensional Heisenberg model with a nearest neighbor magnetic exchange constant J2d = 0.934 +/-0.0025 meV. The inter-layer interaction Jperp in this compound is less than 1.5% of J2d. The spin excitation energy at the (0.5 0.5 0.5) zone boundary point is reduced when compared to the (0.5 1 0.5) zone boundary point by ~10.3 +/- 1.4 %. This zone boundary dispersion is consistent with quantum Monte Carlo and series expansion calculations which include corrections for quantum fluctuations to linear spin wave theory.