Collective impurity effects in the Heisenberg triangular antiferromagnet

TL;DR

This paper theoretically explores how nonmagnetic impurities in a Heisenberg triangular antiferromagnet induce collective effects like localized magnetic moments and degeneracy lifting, revealing new impurity-driven phenomena.

Contribution

It predicts the emergence of localized magnetic moments and degeneracy lifting due to impurities, introducing a novel analytical understanding of impurity effects in frustrated magnets.

Findings

Localized magnetic moments near vacancies cause a Curie tail.

Impurities lift ground-state degeneracy, favoring a conical state.

Vacancies generate positive biquadratic exchange, influencing magnetic behavior.

Abstract

We theoretically investigate the Heisenberg antiferromagnet on a triangular lattice doped with nonmagnetic impurities. Two nontrivial effects resulting from collective impurity behavior are predicted. The first one is related to presence of uncompensated magnetic moments localized near vacancies as revealed by the low-temperature Curie tail in the magnetic susceptibility. These moments exhibit an anomalous growth with the impurity concentration, which we attribute to the clustering mechanism. In an external magnetic field, impurities lead to an even more peculiar phenomenon lifting the classical ground-state degeneracy in favor of the conical state. We analytically demonstrate that vacancies spontaneously generate a positive biquadratic exchange, which is responsible for the above degeneracy lifting.