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

Density-functional theory calculations are carried out on RFeAsO, R=Ce and Pr, the parent compounds of the high-T(c) superconductors RFeAsO(1-x)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 (GGA+U), we show that the R magnetic moments also adopt an antiferromagnetic order for which, within the RO layer, the same spin R sites lie along a zigzag line perpendicular to the Fe spin stripes. While within GGA the R 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, RFeAsO is shown to change from a semimetal to a Mott insulator.