Understanding the $\mu$SR spectra of MnSi without magnetic polarons

TL;DR

This study uses $bc$SR experiments and calculations to precisely characterize the magnetic environment in MnSi, demonstrating that its spectra can be explained without assuming magnetic polarons.

Contribution

The paper provides a detailed analysis of the $bc$SR spectra of MnSi, identifying the muon stopping site and magnetic field distribution without resorting to magnetic polarons, supported by ab initio calculations.

Findings

Angular dependence of muon precession matches Mn-dipolar fields

Field distribution below $T_C$ aligns with zero-field $bc$SR data

Ab initio calculations confirm muon stopping site

Abstract

Transverse-field muon-spin rotation ($\mu$SR) experiments were performed on a single crystal sample of the non-centrosymmetric system MnSi. The observed angular dependence of the muon precession frequencies matches perfectly the one of the Mn-dipolar fields acting on the muons stopping at a 4a position of the crystallographic structure. The data provide a precise determination of the magnetic dipolar tensor. In addition, we have calculated the shape of the field distribution expected below the magnetic transition temperature $T_C$ at the 4a muon-site when no external magnetic field is applied. We show that this field distribution is consistent with the one reported by zero-field $\mu$SR studies. Finally, we present ab initio calculations based on the density-functional theory which confirm the position of the muon stopping site inferred from transverse-field $\mu$SR. In view of the presented evidence we conclude that the $\mu$SR response of MnSi can be perfectly and fully understood without invoking a hypothetical magnetic polaron state.