Fractional impurity moments in two-dimensional non-collinear magnets

TL;DR

This paper investigates how magnetic impurities in two-dimensional non-collinear magnets exhibit fractional moments due to frustration effects, affecting magnetic response and susceptibility.

Contribution

It introduces a quasiclassical approach to quantify impurity contributions in frustrated magnets, revealing non-universal screening and fractional impurity moments.

Findings

Impurity moments are non-quantized and exhibit non-universal screening.

Impurities induce a Curie-like magnetic response at finite temperatures.

Overcompensated impurities show a singular linear-response behavior.

Abstract

We study dilute magnetic impurities and vacancies in two-dimensional frustrated magnets with non-collinear order. Taking the triangular-lattice Heisenberg model as an example, we use quasiclassical methods to determine the impurity contributions to the magnetization and susceptibility. Most importantly, each impurity moment is not quantized, but receives non-universal screening corrections due to local relief of frustration. At finite temperatures, where bulk long-range order is absent, this implies an impurity-induced magnetic response of Curie form, with a prefactor corresponding to a fractional moment per impurity. We also discuss the behavior in an applied magnetic field, where we find a singular linear-response limit for overcompensated impurities, and propose experiments to test our theory.