Abstract
Motivated by the recent discovery of Fe-based superconductors close to an antiferromagnetic insulator in the experimental phase diagram, here the five-orbital Hubbard model (without lattice distortions) is studied using the
√√ real-space Hartree-Fock approximation, employing a 10 × 10 Fe cluster with Fe vacancies in a 5 × 5 pattern.
Varying the Hubbard and Hund couplings, and at electronic density n = 6.0, the phase diagram contains an insulating state with the same spin pattern as observed experimentally, involving 2 × 2 ferromagnetic plaquettes coupled with one another antiferromagnetically. The presence of local ferromagnetic tendencies is in qualitative agreement with Lanczos results for the three-orbital model also reported here. The magnetic moment ∼3μB /Fe is in good agreement with experiments. Several other phases are also stabilized in the phase diagram, in agreement with recent calculations using phenomenological models.
