Microstructure and electronic structure of transparent ferromagnetic ZnO-Spinel iron oxide composite films

Transparent ZnO films with ferromagnetic spinel iron oxide particles (Fe 9.5 atom %) were prepared on glass substrates by a novel chemical process followed by heat treatment at 773 K under vacuum. The chemical process involved (i) ZnO deposition from an aqueous solution and (ii) the introduction of iron atoms into the ZnO in another aqueous solution containing iron ions. The microstructure and electronic structure of the films were characterized in detail by using transmission electron microscope (TEM) analyses, X-ray absorption fine structure (XAFS), and soft X-ray magnetic circular dichroism (SXMCD). TEM observation revealed that the film had a heterogranular structure composed of iron oxide particles of 20 nm in diameter embedded in a wurtzite ZnO matrix. Both the Fe K-edge XAFS and Fe L-2,L-3-edge SXMCD measurements using synchrotron radiation techniques indicated that the iron oxide particles were zinc-substituted magnetite (ZnxFe3-xO4, x approximate to 0.5) with a cubic spine] structure, which is the origin of ferromagnetism. Negative magnetoresistance of -0.35% was found at room temperature as well as an n-type semiconducting feature.