Theoretical investigation of magnetic order inRFeAsO(R=Ce,Pr)

Abstract

Density-functional theory calculations are carried out on $R\text{FeAsO}$, $R=\text{Ce}$ and Pr, the parent compounds of the high-${T}_{c}$ superconductors $R{\text{FeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$, in order to determine the magnetic order of the ground state. It is found that the magnetic moments on the Fe sites adopt an antiferromagnetic order, with a stripelike pattern similar to the case of LaFeAsO. Within the generalized gradient approximation along with Coulomb on-site repulsion $(\text{GGA}+U)$, we show that the $R$ magnetic moments also adopt an antiferromagnetic order for which, within the $R\text{O}$ layer, the same spin $R$ sites lie along a zigzag line perpendicular to the Fe spin stripes. While within GGA the $R\text{ }4f$ band crosses the Fermi level, upon inclusion of on-site Coulomb interaction on the $R$ sites the $4f$ band splits and moves away from the Fermi level. If on-site Coulomb interaction is also included on the Fe sites, $R\text{FeAsO}$ is shown to change from a semimetal to a Mott insulator.