Spin correlations in an isotropic spin-5/2 two-dimensional antiferromagnet

TL;DR

This study investigates spin correlations in a two-dimensional S=5/2 antiferromagnet under magnetic fields, demonstrating alignment with semiclassical theory and providing insights into the classical and quantum regimes of spin behavior.

Contribution

It experimentally explores the spin correlations in a high-spin 2D antiferromagnet near the bicritical point, linking classical and quantum theoretical predictions.

Findings

Correlation length matches semiclassical theory predictions

No evidence of low-temperature quantum regime behavior

Constructed an ideal S=5/2 Heisenberg system

Abstract

We report a neutron scattering study of the spin correlations for the spin 5/2, two-dimensional antiferromagnet Rb_2MnF_4 in an external magnetic field. Choosing fields near the system's bicritical point, we tune the effective anisotropy in the spin interaction to zero, constructing an ideal S=5/2 Heisenberg system. The correlation length and structure factor amplitude are closely described by the semiclassical theory of Cuccoli et al. over a broad temperature range but show no indication of approaching the low-temperature renormalized classical regime of the quantum non-linear sigma model.