Lubna R Shah et al 2009 J. Phys.: Condens. Matter 21 486004 doi:10.1088/0953-8984/21/48/486004
Lubna R Shah1,4, Bakhtyar Ali2, Hao Zhu1, W G Wang1, Y Q Song3, H W Zhang3, S I Shah1,2 and J Q Xiao1,4
Show affiliationsRoom temperature ferromagnetism in polycrystalline CoxCe1−xO2−δ (0.001≤x≤0.10) bulk samples has been investigated. Annealing in the forming gas transformed the as-prepared paramagnetic into a ferromagnetic insulating material with over two orders of magnitude enhancement (from 3.7 × 10−2 to 1.24 μB/Co) in the magnetization. Structural characterization of both the as-prepared and H2-treated samples showed a single phase material. The incorporation of Co with the formation of oxygen vacancies in the oxide lattice was revealed by x-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies is indicated by the existence of mixed valence states of cerium (Ce4+ and Ce3+) in the high resolution XPS 3d spectrum. The role of the donor defects (oxygen vacancies) has been verified through the removal of oxygen vacancies. The ferromagnetic insulating ground state has been explained in terms of the interaction of the F+ center and 3d magnetic cations. The connection between magnetic properties, electronic structure of the magnetic impurity and donor defect has been established. First principle calculations have been performed using the full potential linearized augmented plane wave method within the density functional theory (DFT) framework; these support our experimental findings. Both the experiment and calculations reinforced the crucial role of oxygen vacancies.
61.72.J- Point defects and defect clusters
71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
75.50.Dd Nonmetallic ferromagnetic materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
Condensed matter: electrical, magnetic and optical
Issue 48 (2 December 2009)
Received 12 September 2009, in final form 19 October 2009
Published 11 November 2009
Lubna R Shah et al 2009 J. Phys.: Condens. Matter 21 486004
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