Eur. Phys. J. B 5, 15-22 (1998)
https://doi.org/10.1007/s100510050413

Spin correlations in the two-dimensional spin-5/2 Heisenberg antiferromagnet Rb₂MnF₄

¹ Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
² Department of Physics, Brookhaven National Laboratory, Upton, NY 11973, USA

Corresponding author: ^a robertjb@mit.edu

Received: 3 March 1998
Revised: 4 May 1998
Accepted: 19 May 1998
Published online: 15 September 1998

Abstract

We report a neutron scattering study of the instantaneous spin correlations in the two-dimensional spin S=5/2 square-lattice Heisenberg antiferromagnet Rb₂MnF₄. The measured correlation lengths are quantitatively described, with no adjustable parameters, by high-temperature series expansion results and by a theory based on the quantum self-consistent harmonic approximation. Conversely, we find that the data, which cover the range from about 1 to 50 lattice constants, are outside of the regime corresponding to renormalized classical behavior of the quantum non-linear σ model. In addition, we observe a crossover from Heisenberg to Ising critical behavior near the Néel temperature; this crossover is well described by a mean-field model with no adjustable parameters.