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Atomic-scale studies of cobalt distribution in Co–TiO2 anatase thin films: Processing, microstructure, and the origin of ferromagnetism

Authors :
Kelli A. Griffin
S. J. Pennycook
A. B. Pakhomov
Kannan M. Krishnan
Maria Varela
Source :
Journal of Applied Physics. 99:08M114
Publication Year :
2006
Publisher :
AIP Publishing, 2006.

Abstract

Using high-resolution, aberration-corrected, scanning transmission electron microscopy and electron-energy-loss spectroscopy we show that in films of single-phase anatase Co:TiO2, the Co distribution and magnetic properties are strongly dependent both on the overall crystalline quality and postgrowth vacuum annealing process. The Co:TiO2 films are coherent, epitaxial anatase with no secondary phases or metallic Co. Films of lower crystalline quality reveal a relatively homogeneous Co concentration, while films of higher crystalline quality show a tendency for Co enrichment near the surface region, around grain boundaries, and the substrate interface. Both uniform and nonuniform samples show a notable enhancement in the saturation magnetization with annealing, while the coercive field is considerably higher in the samples with uniform Co distribution. These experiments confirm that films of single-phase anatase Co:TiO2 with both uniform and nonuniform Co distributions exhibit room-temperature ferromagnetism in the insulating ground state, while the compositional uniformity and film microstructure play a role in the bulk magnetic properties of the material and the mechanisms for ferromagnetic ordering.

Details

ISSN :
10897550 and 00218979
Volume :
99
Database :
OpenAIRE
Journal :
Journal of Applied Physics
Accession number :
edsair.doi...........6b60089fc1bc777c9e6d6dee3aedc721
Full Text :
https://doi.org/10.1063/1.2170068