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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 Ce2O2FeSe2 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 nearest-neighbor Fe-Se-Fe interactions in the ZrCuSiAs-related iron oxyselenide Ce2O2FeSe2. Inelastic measurements provide an estimate of the strength of nearest-neighbor Fe-Fe and Fe-Ce interactions. These are consistent with density functional theory calculations, which reveal that correlations in the Fe-Se sheets of Ce2O2FeSe2 are weak. The Fe on-site repulsion UFe is comparable to that reported for oxyarsenides and K1-xFe2-ySe2, which are parents to iron-based superconductors. [ABSTRACT FROM AUTHOR]

We present here an investigation of the magnetic ordering in the Mott insulating oxyselenide materials Ln2O2Fe2OSe2 (Ln=Ce, Nd). Neutron powder diffraction data are consistent with a noncollinear multi-k ordering on the iron sublattice structure and analysis indicates a reduced magnetic correlation length perpendicular to the [Fe2O]2+ layers. The magnetic role of the Ln3+ cations is investigated and Ce3+ moments are found to order at T⩽16 K. [ABSTRACT FROM AUTHOR]

Identifying and characterizing the parent phases of iron-based superconductors is an important step towards understanding the mechanism for their high-temperature superconductivity. We present an investigation into the magnetic interactions in the Mott insulator La2O2Fe2OSe2. This iron oxyselenide adopts a 2-k magnetic structure with low levels of magnetic frustration. This magnetic ground state is found to be dominated by next-nearest-neighbor interactions J2 and J2' and the magnetocrystalline anisotropy of the Fe2+ site, leading to 2D-Ising-like spin S=2 fluctuations. In contrast to calculations, the values are small and confine the spin excitations below ~25 meV. This is further corroborated by sum rules of neutron scattering. This indicates that superconductivity in related materials may derive from a weakly coupled and unfrustrated magnetic structure. [ABSTRACT FROM AUTHOR]

Magnetic oxyselenides have been a topic of research for several decades, firstly in the context of photoconductivity and thermoelectricity owing to their intrinsic semiconducting properties and ability to tune the energy gap through metal ion substitution. More recently, interest in the oxyselenides has experienced a resurgence owing to the possible relation to strongly correlated phenomena given the fact that many oxyselenides share a similar structure to unconventional superconducting pnictides and chalcogenides. The two dimensional nature of many oxyselenide systems also draws an analogy to cuprate physics where a strong interplay between unconventional electronic phases and localised magnetism has been studied for several decades. It is therefore timely to review the physics of the oxyselenides in the context of the broader field of strongly correlated magnetism and electronic phenomena. Here we review the current status and progress in this area of research with the focus on the influence of lanthanides and transition metal ions on the intertwined magnetic and electronic properties of oxyselenides. The emphasis of the review is on the magnetic properties and comparisons are made with iron based pnictide and chalcogenide systems.