First-principles investigations of the orbital magnetic moments in CrO2

The electronic and magnetic properties of the ferromagnetic half-metal CrO2 have been studied by using the full-potential linear muffin-tin orbital method within the local-spin-density approximation (LSDA) and the LSDA+U approach. The orbital magnetic moments are investigated by including the spin-orbit coupling in both schemes. Compared with the orbital contributions to magnetization in other transition metal oxides, the orbital magnetic moment of the Cr atom is quenched, while the O atoms exhibit a relatively significant orbital moment in CrO2. The LSDA gives the orbital moments of -0.037mu(B)/Cr and -0.0011mu(B)/O. They are too small as compared with the moments of -0.05mu(B)/Cr and -0.003mu(B)/O obtained from x-ray magnetic circular dichroism measurements. By taking the on-site Coulomb energy U into account, both the spin and orbital magnetic moments of Cr and O are dramatically enhanced. For a Hubbard U of 3 eV, the LSDA+U gives orbital moments of -0.051mu(B)/Cr and -0.0025mu(B)/O, in good agreement with the experimental orbital moments. Both the spin and orbital moments are found to increase more or less linearly with increasing U. Similar trends have also been found in CoO and NiO. (C) 2002 American Institute of Physics.