The Magnetic Structure of Paramagnetic MnO

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.