Impurity Conduction and Magnetic Polarons in Antiferromagnetic Oxides

TL;DR

This study investigates impurity conduction and magnetic polarons in antiferromagnetic oxides SrMnO3 and CaMnO3, revealing impurity bands, carrier excitation mechanisms, and challenging existing theories on magnetic polaron formation.

Contribution

It provides experimental evidence of impurity bands and carrier excitation in antiferromagnetic oxides, questioning the predicted formation of self-trapped magnetic polarons.

Findings

Impurity bands of mobile states are identified in SrMnO3 and CaMnO3.

Weak electric fields can significantly increase mobile carrier concentration.

Data suggest bound magnetic polarons are stable only at very low temperatures.

Abstract

Low-temperature transport and magnetization measurements for the antiferromagnets SrMnO(3) and CaMnO(3) identify an impurity band of mobile states separated by energy E from electrons bound in Coulombic potentials. Very weak electric fields are sufficient to excite bound electrons to the impurity band, increasing the mobile carrier concentration by more than three orders of magnitude. The data argue against the formation of self-trapped magnetic polarons (MPs) predicted by theory, and rather imply that bound MPs become stable only for kT<<E.