Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and \textit{ab initio} theory

TL;DR

This study combines neutron scattering experiments and extit{ab initio} calculations to verify that Anderson superexchange is the dominant magnetic interaction in MnO, confirming a long-standing theoretical model.

Contribution

The paper provides experimental verification and extit{ab initio} theoretical support for Anderson superexchange as the primary magnetic interaction in MnO.

Findings

Magnetic PDF analysis confirms known antiferromagnetic structure at low temperature.

Short-range magnetic correlations differ from long-range order in the paramagnetic phase.

extit{Ab initio} calculations accurately reproduce magnetic correlations dominated by Anderson superexchange.

Abstract

We present temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a $\sim$1~nm length scale that differ substantially from the low-temperature long-range spin arrangement. \textit{Ab initio} calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experiment and confirmed by \textit{ab initio} theory.