Magnetic states of the five-orbital Hubbard model for one-dimensional iron-based superconductors

The magnetic phase diagrams of models for quasi-one-dimensional compounds belonging to the iron-based-superconductor family are presented. The five-orbital Hubbard model and the real-space Hartree-Fock approximation are employed, supplemented by density functional theory to obtain the hopping amplitudes. Phase diagrams are constructed by varying the Hubbard U and Hund J couplings at zero temperature. The study is carried out at electronic density (electrons per iron) n = 5.0, which is of relevance for the already-known material T1FeSe(2), and also at n = 6.0, where representative compounds still need to be synthesized. At n = 5.0 there is a clear dominance of staggered spin order along the chain direction. At n = 6.0 and with the realistic Hund coupling J/U = 0.25, the phase diagram is far richer, including a variety of "block" states involving ferromagnetic clusters that are antiferromagnetically coupled, in qualitative agreement with recent density matrix renormalization group calculations for the three-orbital Hubbard model in a different context. These block states arise from the competition between ferromagnetic order (induced by double exchange and prevailing at large J/U) and antiferromagnetic order (dominating at small J/U). The density of states and orbital compositions of the many phases are also provided.