title: Strong room-temperature ferromagnetism in Co2+-doped TiO2 made from colloidal nanocrystals.
abstract: Colloidal cobalt-doped TiO(2) (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 (M(s) approximately 1.5 x 10(-)(3) micro(B)/Co(2+) at 300 K) when aggregated, and strongly ferromagnetic (up to M(s) = 1.9 micro(B)/Co(2+) at 300 K) when spin-coated into nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co(2+) oxidation state in all samples. In addition to providing strong experimental support for the existence of intrinsic ferromagnetism in cobalt-doped TiO(2), these results demonstrate the possibility of using colloidal TiO(2) diluted magnetic semiconductor nanocrystals as building blocks for assembly of ferromagnetic semiconductor nanostructures with potential spintronics applications.
authors.affiliation: Contribution from the Department of Chemistry, University of Washington, Seattle, WA 98195-1700, USA.
authors.forename: J Daniel
authors.initials: JD
authors.lastname: Bryan
authors.forename: Steve M
authors.initials: SM
authors.lastname: Heald
authors.forename: Scott A
authors.initials: SA
authors.lastname: Chambers
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Gamelin