First-Principles Calculation of the Orbital Magnetic Moment of O and Cr in Half-metallic CrO 2
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First-principles Calculation of the Orbital Magnetic Moment of O and Cr in Half-metallic CrO2 Horng-Tay Jeng and G. Y. Guo1 Physics Division, National Center for Theoretical Sciences, Hsinchu 300, Taiwan 1 Department of Physics, National Taiwan University, Taipei 106, Taiwan ABSTRACT The electronic and magnetic properties of half-metallic CrO2 have been studied by using the full-potential linearized muffin-tin orbital method within the local spin-density approximation (LSDA)+U approach. It is found that the orbital magnetic moment of Cr atom is quenched while O atom exhibit relatively significant orbital moment in CrO2. For the Hubbard U of 3 eV, LSDA+U gives the orbital moment of -0.051µB/atom for Cr and -0.0025µB/atom for O, being in good agreement with the experimental orbital moments of -0.05 for Cr and -0.003µB/atom for O, respectively. In contrast, LSDA gives the orbital moment of -0.037 for Cr and -0.0011 µB/atom for O, being too small as compared with the magnetic circular dichroism measurements. For the larger U considered in this work, both spin and orbital moments almost increase linearly with respect to U. INTRODUCTION CrO2 is a ferromagnetic half-metal with a magnetic moment of 2 µB per formula units (fu) [1]. It has been widely used in magnetic recording tapes. In recent years, it attracts substantial interests because of the half-metallic property and the applicable potential for future spintronics. In half-metal CrO2, one spin channel is metallic and the other is insulating, resulting in an unusual transport property of 100 % spin polarization. The Fermi level lies in the partially filled 3d band of the majority spin, whereas in the minority spin, the Fermi energy falls in an exchange-split gap between the occupied oxygen 2p band and the unoccupied chromium 3d band. By the formation of a pseudogap at the Fermi level in the conducting majority spin of the ferromagnetic CrO2, the large density of state at the Fermi energy of the paramagnetic CrO2 is stabilized according to the usual Stoner argument [2]. Since the states involving the conduction and magnetic properties are highly spin-polarized near the Fermi energy, it is therefore interesting to investigate the orbital contributions of the individual atoms to the magnetic moment of CrO2. The orbital magnetic moments are usually suppressed in the 3d transition metals because of the crystal field in solids. Some 3d transition metal oxides exhibit large unquenched orbital magnetic moments. The unquenched orbital moment arises mainly from the spin-orbit interaction in the localized 3d orbital where the atomic field is deformed in a relatively slight manner by the crystal field. The strong Coulomb correlations further localize the 3d orbitals and suppress the ligand field on the metal atoms. These materials are thus expected to possess larger unquenched orbital moments. It has been found in neutron-diffraction experiment for CoO [3], and in magnetic x-ray scattering experiment for NiO [4] that the unquenched orbital magnetic moments are rather large. Altho
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