New insights for the description of magnetic correlations inferred from muSR

TL;DR

This paper critically examines how muSR measurements are interpreted for magnetic ordering, highlighting potential pitfalls and proposing a new analysis method based on maximum entropy and reverse Monte Carlo techniques.

Contribution

It introduces a novel analysis approach for muSR data that accounts for short-range correlations, improving the reliability of magnetic structure characterization.

Findings

Spontaneous muSR oscillations do not necessarily indicate large coherence length.

Incommensurate magnetic structures may be misinterpreted from muSR data alone.

The proposed maximum entropy and reverse Monte Carlo method yields consistent results with previous analytical approaches.

Abstract

Whenever a compound exhibits a spontaneous muSR oscillation, long-range magnetic ordering is usually inferred. Here we show that some caution is required. The coherence length needs not to be large for a spontaneous muon spin precession to be observed. Establishing the incommensurate nature of a magnetic structure, solely based on muSR measurements, may not be reliable. The absence of a spontaneous muon precession at low temperature does not mean that the system under investigation does not display long-range magnetic ordering. The relaxation measured in zero and longitudinal field in the quasi-static limit is usually analyzed in the framework of the strong-collision model, the static polarization function being taken to be the famous Kubo-Toyabe function. This might not be satisfactory if short-range correlation effects are strong. Here we propose a method based on the maximum entropy concept and reverse Monte Carlo technique which gives results consistent with those obtained in 2013 by analytical means for the considered example.