Thermodynamics of isotropic and anisotropic layered magnets: renormalization group approach and 1/N expansion

TL;DR

This paper uses renormalization group and 1/N expansion methods to analyze the thermodynamics of layered isotropic and anisotropic magnets, providing analytical and numerical results that align with experimental data and Monte Carlo simulations.

Contribution

It introduces a combined RG and 1/N expansion approach to study layered magnetic systems, including quantum and classical regimes, and derives temperature-dependent magnetization and ordering temperature results.

Findings

Good agreement with experimental data on layered perovskites

Analytical temperature dependence of magnetization obtained

RG results for ordering temperature match 1/N expansion in quantum case

Abstract

The O(N) model of layered antiferro- and ferromagnets with a weak interlayer coupling and/or easy-axis anisotropy is considered. A renormalization group (RG) analysis in this model is performed, the results for N=3 being expected to agree with those of the 1/M expansion in the CP^{M-1} model at M=2. The quantum and classical cases are considered. A crossover from an isotropic 2D-like to 3D Heisenberg (or 2D Ising) regime is investigated within the 1/N expansion. Analytical results for the temperature dependence of the (sublattice) magnetization are obtained in different regimes. The RG results for the ordering temperature are derived. In the quantum case they coincide with the corresponding results of the 1/N expansion. The numerical calculations on the base of the equations obtained yield a good agreement with experimental data on the layered perovskites La2CuO4, K2NiF4 and Rb2NiF4, and the Monte Carlo results for the anisotropic classical systems.