Magnetic Phase Diagram of a Five-Orbital Hubbard Model in the Real-Space Hartree Fock Approximation Varying the Electronic Density

TL;DR

This study maps the magnetic phase diagram of a five-orbital Hubbard model for iron-based superconductors using real-space Hartree Fock, revealing various magnetic states and phase separation as electronic density varies.

Contribution

It provides the first detailed phase diagram of a five-orbital Hubbard model across different electron densities using real-space Hartree Fock, highlighting new magnetic states.

Findings

At n=5, a G-type antiferromagnetic insulator is observed.

Increasing n leads to more ferromagnetic links and diverse magnetic states.

Phase separation regions are identified in the phase diagram.

Abstract

Using the real-space Hartree Fock approximation, the magnetic phase diagram of a five-orbital Hubbard model for the iron-based superconductors is studied varying the electronic density $n$ in the range from 5 to 7 electrons per transition metal atom. The Hubbard interaction $U$ is also varied, at a fixed Hund coupling $J/U=0.25$. Several qualitative trends and a variety of competing magnetic states are observed. At $n$=5, a robust G-type antiferromagnetic insulator is found, in agreement with experimental results for BaMn$_2$As$_2$. As $n$ increases away from 5, magnetic states with an increasing number of nearest-neighbors ferromagnetic links become energetically stable. This includes the well-known C-type antiferromagnetic state at $n$=6, the E-phase known to exist in FeTe, and also a variety of novel states not found yet experimentally, some of them involving blocks of ferromagnetically oriented spins. Regions of phase separation, as in Mn-oxides, have also been detected. Comparison with previous theoretical investigations indicate that these qualitative trends may be generic characteristics of phase diagrams of multiorbital Hubbard models.