Suppression of antiferromagnetic correlations by quenched dipole--type impurities

TL;DR

This paper investigates how quenched dipole-type impurities affect antiferromagnetic correlations in a 2D Heisenberg model, showing that even small concentrations destroy long-range order and significantly alter the correlation length and Néel temperature.

Contribution

It introduces a renormalization group analysis of dipolar impurities' effects on antiferromagnetic order, providing quantitative predictions aligned with experimental data on doped copper oxides.

Findings

Antiferromagnetic order is destroyed at any non-zero impurity concentration.

Correlation length becomes temperature-independent below a certain line.

Néel temperature decreases linearly with impurity concentration and drops sharply at a critical point.

Abstract

The effect of quenched random ferromagnetic bonds on the antiferromagnetic correlation length of a two--dimensional Heisneberg model is studied, applying the renormalization group method to the classical non--linear sigma model with quenched random dipole moments. It is found that the antiferromagnetic long range order is destroyed for any non--zero concentration, of the dipolar defects, even at zero temperature. Below a line T ~ concentration, the correlation length is independent of T, and decreases exponentially with concentration. At higher temperatures, itdecays exponentially with an effective stiffness constant which decreases with concentration/T. The results are used to estimate the three--dimensional N\'{e}el temperature, which decays linearly with $x$ at small concentrations, and drops precipitously at a critical concentration. These predictions are compared with experiments on doped copper oxides, and are shown to reproduce successfully some of the prominent features of the data.