Doping effects on the valence band of Tl2Mn2O7 pyrochlores: Relation to magnetoresistance

Sánchez-Benítez, J.; de Andrés, A.; Prieto, C.; Ávila, J.; Martín-Carrón, L.; Martínez, J. L.; Alonso, J. A.; Martínez-Lope, M. J.; Casais, M. T.
May 2004
Applied Physics Letters;5/24/2004, Vol. 84 Issue 21, p4209
Academic Journal
Photoemission and x-ray absorption near edge spectroscopy measurements have been performed in Tl2Mn2O7 oxides doped with 10% different ions, Bi, Cd, or Sb, which produce colossal changes in the magnetoresistance values. The contributions to the valence band related to Mn, O, and the doping ions have been obtained. We found that the paramagnetic phase of doped Tl pyrochlores is charge-transfer insulator type with oxygen character of the upper edge of the valence band. Bi 6s and Cd 4d orbitals lie also at the upper edge of the valence band. Mn valence is identical for all samples while oxygen content varies to compensate for the charge introduced by doping. The density of carriers, which is correlated to the magnetoresistance values, is determined by the density of states near the Fermi level provided by Tl and O content. © 2004 American Institute of Physics.


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