Spin excitations in paramagnetic MnO

Manganese(II) oxide, MnO, is a well-studied and well understood Anti-ferromagnet (AFM) in its low-temperature phase (<118 K), but the full magnetic character of its low-temperature paramagnetic regime (118 < T < 600 K) remains a mystery. Triangular motifs in the face-centered cubic lattice create geometrical frustration, driving strong spin correlations to persist in the paramagnetic regime. We have recently demonstrated how the combination of this geometrical frustration and magnetoelastic coupling creates local AFM magnetic domains well within the paramagnetic phase. Any magnetically ordered domain is expected to support magnetic excitations, and indeed, these were previously detected in paramagnetic MnO. However, it is unclear to what extent spin-wave theory remains valid under these circumstances and whether the magnetic wave character will agree with our local domain picture. To test whether magnetoelastic coupling can drive local lattice relaxation within the paramagnetic regime and elucidate the nature of its magnetic excitations, we propose to carry out a modern set of inelastic neutron scattering measurements. Comparing the results with Monte-Carlo simulations and supercell lattice dynamics will allow us to determine the excitation spectrum for paramagnetic MnO, visualise the spin excitations within a local domain description and interpret the findings in the framework of spin-phonon interactions.