The Magnetic Structure of Paramagnetic MnO

TL;DR

This study uncovers a locally-ordered domain structure in paramagnetic MnO at 160K, revealing complex spin correlations that differ from the antiferromagnetic state and have broader implications for weakly-frustrated systems.

Contribution

It provides a detailed microscopic picture of paramagnetic MnO using neutron scattering and Monte Carlo methods, highlighting persistent local order beyond traditional correlation lengths.

Findings

Locally-ordered domains extend over large distances.

Directional spin correlations differ from antiferromagnetic order.

Implications for understanding paramagnetic states in frustrated systems.

Abstract

Using a combination of single-crystal neutron scattering and reverse Monte Carlo refinements, we study the magnetic structure of paramagnetic MnO at a temperature (160\,K) substantially below the Curie-Weiss temperature $|\theta|\sim550$\,K. The microscopic picture we develop reveals a locally-ordered domain structure that persists over distances many times larger than the correlation length implied by direct analysis of the spin correlation function. Moreover, the directional dependence of paramagnetic spin correlations in paramagnetic MnO differs in some important respects from that of its incipient ordered antiferromagnetic state. Our results have implications for the understanding of paramagnetic states in weakly-frustrated systems, including high-temperature superconductors.