Ab initioinvestigation of the noncollinear magnetic structure of CeFeAsO

Abstract

The noncollinear magnetic ground state in CeFeAsO has been investigated using the density-functional theory. When the spin-orbit coupling is discarded, the magnitude of the Ce-magnetic moment (0.87\ensuremath{\mu}${}_{\mathrm{B}}$) is independent of the spin direction and is in accordance with the experimental value of 0.83(2)\ensuremath{\mu}${}_{\mathrm{B}}$. However, when the spin-orbit coupling is considered, the Ce-orbital moments change with the internal magnetic field and affect the total magnetic moment of Ce. One type of Ce ions has a magnetic moment of 0.909\ensuremath{\mu}${}_{\mathrm{B}}$, which is very close to the experimental value. The other type of Ce ions has a magnetic moment of 0.488\ensuremath{\mu}${}_{\mathrm{B}}$, which has not been previously reported. The magnetic moments of the rare-earth metals in NdFeAsO and PrFeAsO are also twice those of experimental observations. The difference between the rare earth magnetic-moment errors of the three compounds imply that magnetism is related to the onset of the superconducting critical temperature. At the same time, the calculated Fe-magnetic moments in all solutions are over 2.0\ensuremath{\mu}${}_{\mathrm{B}}$. From the band structure and density of states (DOS), the Ce 4$f$ and Fe 3$d$ orbits are shown to have major contributions to the Fermi level. Four bands in CeFeAsO cross the Fermi level at the \ensuremath{\Gamma} (0, 0, 0) point and form four hole-like pockets. The superexchange interaction between the Ce 4$f$ and Fe 3$d$ electrons via oxygen ions is discussed. Furthermore the results show that the Fermi surface shape varies with the Ce spin direction, revealing that electroconductibility is directly affected by the Ce-spin direction. If the Ce spin is perpendicular to the FeAs plane, the electronic field gradient (EFG) changes from a negative value into a positive value.