Web Release Date: August 24,
Strong Room-Temperature Ferromagnetism in Co2+-Doped TiO2 Made from Colloidal Nanocrystals
and
Contribution from the Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, and Fundamental Science Directorate, Pacific Northwest National Laboratory, P.O. Box 999, MS K8-93, Richland, Washington 99352
Received May 4, 2004
Abstract:
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 × 10-3 
B/Co2+ at 300 K) when aggregated, and strongly ferromagnetic (up to Ms = 1.9 B/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.
Download the full text: PDF | HTML
