Magnetism of the Fe super(2+) and Ce super(3+) sublattices in Ce sub(2) O sub(2) FeSe sub(2): A combined neutron powder diffraction, inelastic neutron scattering, and density functional study

The discovery of superconductivity in the 122 iron selenide materials above 30 K necessitates an understanding of the underlying magnetic interactions. We present a combined experimental and theoretical investigation of magnetic and semiconducting Ce sub(2) O sub(2) FeSe sub(2) composed of chains of edge-linked iron selenide tetrahedra. The combined neutron diffraction and inelastic scattering study and density functional calculations confirm the ferromagnetic nature of nearestneighbor Fe-Se-Fe interactions in the ZrCuSiAs-related iron oxyselenide Ce sub(2) O sub(2) FeSe sub(2). Inelastic measurements provide an estimate of the strength of nearestneighbor Fe-Fe and Fe-Ce interactions. These are consistent with density functional theory calculations, which reveal that correlations in the Fe-Se sheets of Ce sub(2) O sub(2) FeSe sub(2) are weak. The Fe on-site repulsion U sub(Fe) is comparable to that reported for oxyarsenides and K sub(1-x) Fe sub(2-y) Se sub(2), which are parents to iron-based superconductors.