Local Electronic Structure and Dynamics of Muon-Polaron Complexes in Fe$_2$O$_3$

TL;DR

This study uses muon spin rotation to investigate muon-polaron complexes in Fe$_2$O$_3$, revealing their influence on magnetic properties and implications for hydrogen impurities affecting charge carriers.

Contribution

It provides the first detailed analysis of muon-polaron complexes in Fe$_2$O$_3$, linking muon behavior to hydrogen impurity effects in this material.

Findings

Charge-neutral muon states significantly affect $bc$SR signals.

Muon-polaron complexes are identified as key to understanding charge dynamics.

Hydrogen impurities may form similar complexes influencing conductivity.

Abstract

We perform detailed muon spin rotation ($\mu$SR) measurements in the classic antiferromagnet Fe$_2$O$_3$ and explain the spectra by considering dynamic population and dissociation of charge-neutral muon-polaron complexes. We show that charge-neutral muon states in Fe$_2$O$_3$, despite lacking the signatures typical of charge-neutral muonium centers in nonmagnetic materials, have a significant impact on the measured $\mu$SR frequencies and relaxation rates. Our identification of such polaronic muon centers in Fe$_2$O$_3$ suggests that isolated hydrogen (H) impurities form analogous complexes, and that H interstitials may be a source of charge carrier density in Fe$_2$O$_3$.