Abstract
Whenever a compound exhibits a spontaneous μSR 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 μSR 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.
Highlights
In this report we consider problems relevant for the analysis of experimental positive muon spectroscopy data recorded for a magnetic compound
Inferring a magnetic structure to be incommensurate with only μSR data at hand does not seem reasonable
The μSR technique is well adapted for the study of quasi-static magnetic dynamics, i.e. with dynamics in the micro- and nanosecond time scale
Summary
In this report we consider problems relevant for the analysis of experimental positive muon spectroscopy (μSR) data recorded for a magnetic compound. A relatively short ξm of about ten interatomic distances is enough to give rise to a detectable spontaneous field This result is qualitatively independent of the type of magnetic structure and the muon site. 3. Commensurate versus incommensurate magnetic order An increasing number of observed spontaneous oscillations are found to be well accounted for by a zeroth-order Bessel function of the first kind, rather than a simple cosine. Commensurate versus incommensurate magnetic order An increasing number of observed spontaneous oscillations are found to be well accounted for by a zeroth-order Bessel function of the first kind, rather than a simple cosine From this observation it is inferred that the magnetic structure of the compound under study is incommensurate.
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