Browsing by Author "Fujimori, A"

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Orbital ordering in La0.5Sr1.5MnO4 studied by soft x-ray linear dichroism
(2004-02-27)
Huang, DJ
;
Wu, WB
;
Guo, GY
;
Lin, HJ
;
Hou, TY
We found that the conventional model of orbital-ordering of 3x(2)-r(2)/3y(2)-r(2) type in the e(g) states of La0.5Sr1.5MnO4 is incompatible with measurements of linear dichroism in the Mn 2p-edge x-ray absorption, whereas these e(g) states exhibit predominantly cross-type orbital ordering of x(2)-z(2)/y(2)-z(2). LDA+U band-structure calculations reveal that such a cross-type orbital-ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions.
Orbital polarization of LaSrMnO4 studied by soft X-ray linear dichroism
(2004-07-01)
Wu, WB
;
Huang, DJ
;
Guo, GY
;
Lin, H
;
Hou, TY
With polarization-dependent soft X-ray absorption, we determined the orbital character of occupied and the lowest unoccupied e, orbitals of prototype single-layered perovskite LaSrMnO4, Our measurements indicate that LaSrMnO4 exhibits strong orbital polarization in the e, states of Mn3+ sites, leading us to conclude that LaSrMnO4 has a "ferro-orbital" ordering of 3z(2)-r(2). We found that linear dichroism in soft X-ray absorption is an effective experimental method to identify the nature of orbital ordering in transition-metal oxides such as manganites. (C) 2004 Elsevier B.V. All rights reserved.
Orbital symmetry and electron correlation in NaxCoO2
(2005-04-15)
Wu, WB
;
Huang, DJ
;
Okamoto, J
;
Tanaka, A
;
Lin, HJ
Measurements of polarization-dependent soft x-ray absorption reveal that the electronic states determining the low-energy excitations of NaxCoO2 have predominantly a(1g) symmetry with significant O 2p character. In contrast to the prediction of band theory, doping-dependent O 1s x-ray absorption shows a large transfer of spectral weight, providing spectral evidence for strong electron correlations of the layered cobaltates. We also found that NaxCoO2 exhibits a charge-transfer electronic character rather than a Mott-Hubbard character.
Spin and orbital magnetic moments of Fe3O4
(2004-08-13)
Huang, DJ
;
Chang, CF
;
Jeng, HT
;
Guo, GY
;
Lin, HJ
We present measurements of the spin and orbital magnetic moments of Fe3O4 by using SQUID and magnetic circular dichroism in soft x-ray absorption. The measurements show that Fe3O4 has a noninteger spin moment, in contrast to its predicted half-metallic feature. Fe3O4 also exhibits a large unquenched orbital moment. Calculations using the local density approximation including the Hubbard U method and the configuration interaction cluster-model suggest that strong correlations and spin-orbit interaction of the 3d electrons result in the noninteger spin and large orbital moments of Fe3O4.