Finite-temperature ordering in two-dimensional magnets

Abstract

We study the two dimensional quantum Heisenberg antiferromagnet on the square lattice with easy-axis exchange anisotropy. By the semiclassical method called pure-quantum self-consistent harmonic approximation we analyse several thermodynamic quantities and investigate the existence of a finite temperature transition, possibly describing the low-temperature critical behaviour experimentally observed in many layered real compounds. We find that an Ising-like transition characterizes the model even when the anisotropy is of the order of $10^{-2}J$ ($J$ being the intra-layer exchange integral), as in most experimental situations. On the other hand, typical features of the isotropic Heisenberg model are observed for both values of anisotropy considered, one in the {\it quasi}-isotropic limit and the other in a more markedly easy-axis region. The good agreement found between our theoretical results and the experimental data relative to the real compound Rb${}_2$MnF${}_4$ shows that the insertion of the easy-axis exchange anisotropy, with quantum effects properly taken into account, provides a quantitative description and explanation of the experimental data, thus allowing to recognize in such anisotropy the main agent for the observed onset of finite temperature long-range order.

To appear on Phys. Rev. B

References in corpus (4)

• Spin Correlations in the Two-Dimensional Spin-5/2 Heisenberg Antiferromagnet Rb2MnF4
• Low Temperature Static and Dynamic Behavior of the Two-Dimensional Easy-Axis Heisenberg Model
• The correlation length of the Heisenberg antiferromagnet with arbitrary spin S
• Effective Hamiltonian with holomorphic variables

Cited by in corpus (5)

• Quantum Monte Carlo study of S=1/2 weakly-anisotropic antiferromagnets on the square lattice
• A study of the quantum classical crossover in the spin dynamics of the 2D S=5/2 antiferromagnet Rb2MnF4: neutron scattering, computer simulations, and analytic theories
• Reentrant enhancement of quantum fluctuations for symmetric environmental coupling
• Anisotropy and Ising-like transition of the S=5/2 two-dimensional Heisenberg antiferromagnet Mn-formate di-Urea
• Quantum Heisenberg antiferromagnets: a survey of the activity in Firenze