Spin Correlations in the Geometrically Frustrated RBaCo4O7 Antiferromagnets: Mean-Field Approach and Monte-Carlo Simulations

TL;DR

This study investigates spin correlations in RBaCo4O7 antiferromagnets using mean-field theory and Monte-Carlo simulations, revealing how exchange interactions influence magnetic order and frustration effects.

Contribution

It provides a combined mean-field and Monte-Carlo analysis of how exchange ratios affect magnetic ordering in geometrically frustrated RBaCo4O7 compounds.

Findings

Long-range order appears for Jout/Jin > 0.7 in mean-field calculations.

Ground state with long-range order occurs for Jout/Jin > 1.5 in Monte-Carlo simulations.

Short-range 120° correlations dominate in the (ab) plane at lower Jout/Jin ratios.

Abstract

Spin correlations in the geometrically frustrated RBaCo4O7 compounds, usually described as an alternating stacking of Kagome and triangular layers on a hexagonal lattice, have been studied by mean-field approach and by Monte-Carlo simulations. The behavior of the system was modelled with an isotropic Heisenberg Hamiltonian as a function of the relevant parameter Jout/Jin, representing the ratio between exchange integrals inside the Kagome layers, Jin, and between Kagome and triangular layers, Jout. This ratio can be varied in real systems by appropriate chemical substitutions. At the mean-field level, long-range magnetic order with the wave vector at the K-point of symmetry (k=a*/3+b*/3) has been found for Jout/Jin>0.7. Below this value, the dominant Fourier modes are completely degenerate in the entire Brillouin zone. The Monte-Carlo simulations revealed that the long-range ordered configuration found in the mean-field calculations becomes the ground state of the system for Jout/Jin>1.5. Below this critical ratio, quasi one-dimensional magnetic ordering along the c-axis, involving spins of the triangular sublattice was observed. The correlations in the (ab) plane were found to have a short-range 120o character with correlation length dependent on Jout/Jin.