Colloidal cobalt-doped TiO2 (anatase) nanocrystals were synthesized and studied by electronic absorption, magnetic circular dichroism, transmission electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption spectroscopy, and extended X-ray absorption fine structure measurements. The nanocrystals were paramagnetic when isolated by surface-passivating ligands, weakly ferromagnetic (Ms = 1.5 x 10-3 mB/Co2+ at 300 K) when aggregated, and strongly ferromagnetic (up to Ms = 1.9 mB/Co2+ at 300 K) when spin-coated into nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co2+ oxidation state in all samples. In addition to providing strong experimental support for the existence of intrinsic ferromagnetism in cobalt-doped TiO2, these results demonstrate the possibility of using colloidal TiO2 diluted magnetic semiconductor nanocrystals as building blocks for assembly of ferromagnetic semiconductor nanostructures with potential spintronics applications.
@article{arxiv.cond-mat/0407451,
title = {Strong Room-Temperature Ferromagnetism in Co2+-Doped TiO2 made from Colloidal Nanocrystals},
author = {J. Daniel Bryan and Steve M. Heald and Scott A. Chambers and Daniel R. Gamelin},
journal= {arXiv preprint arXiv:cond-mat/0407451},
year = {2007}
}
Comments
To be published in the Journal of the American Chemical Society