Magnetic order in orbital models of the iron pnictides

TL;DR

This study investigates magnetic order in five orbital models of iron pnictides, revealing that stripe magnetic order depends on Fermi surface nesting and electronic structure details, with implications for understanding their magnetic properties.

Contribution

It provides a comparative analysis of five orbital models, showing how magnetic order arises and its sensitivity to electronic structure details in iron pnictides.

Findings

Stripe magnetic order is possible in four models.

Order is highly sensitive to Fermi surface nesting.

Competing incommensurate states are influenced by low-energy electronic structure.

Abstract

We examine the appearance of the experimentally-observed stripe spin-density-wave magnetic order in five different orbital models of the iron pnictide parent compounds. A restricted mean-field ansatz is used to determine the magnetic phase diagram of each model. Using the random phase approximation, we then check this phase diagram by evaluating the static spin susceptibility in the paramagnetic state close to the mean-field phase boundaries. The momenta for which the susceptibility is peaked indicate in an unbiased way the actual ordering vector of the nearby mean-field state. The dominant orbitally resolved contributions to the spin susceptibility are also examined to determine the origin of the magnetic instability. We find that the observed stripe magnetic order is possible in four of the models, but it is extremely sensitive to the degree of the nesting between the electron and hole Fermi pockets. In the more realistic five-orbital models, this order competes with a strong-coupling incommensurate state which appears to be controlled by details of the electronic structure below the Fermi energy. We conclude by discussing the implications of our work for the origin of the magnetic order in the pnictides.