Diluted magnetic semiconductor Zn1−xCoxO nanorods with a Curie temperature higher than 350K have been synthesized by in situ doping of Co in ZnO nanorods using a simple thermal chemical vapor deposition method. Structural analyses indicated that the nanorod possesses the single-crystalline wurtzite structure and there is no segregated cluster of impurity phase appearing throughout the nanorod. The transparence of the Zn1−xCoxO nanorods in the visible region has been examined by UV-visible absorption. The fundamental absorptions of the Zn1−xCoxO nanorods estimated from the absorption spectra do not reveal pronounced difference from that of pure ZnO nanorods.

X-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed for Zn1−xCoxO and Zn1−xMgxO to elucidate the effects of the doping of Co and Mg, which have very different electronegativities, on the electronic structures of ZnO nanorods. The intensities of O K-edge near-edge features in the XANES spectra of Zn1−xCoxO and Zn1−xMgxO nanorods are found to be lower than those of ZnO, which suggests that both Co and Mg substitutions of the Zn ions enhance the effective charge on the O ion. The valence-band SPEM measurements show that Mg doping does not increase the density of near-Fermi-level states, which implies that Mg doping will not improve field emission of ZnO nanorods. It is surprising to find that both Co and Mg substitutions of Zn increase the numbers of O 2p dominated valence-band states, despite that Co and Mg have larger and smaller electronegativities than that of Zn.

This work investigates the electronic and ferromagnetic properties of Zn1−xCoxO nanorods using x-ray absorption, x-ray magnetic circular dichroism, and scanning photoelectron microscopy methods. The magnetic moment of Co ions in Zn1−xCoxO nanorods is found greatly reduced relative to that of the Co metal. The intensities of valence-band features near the valence-band maximum/Fermi level (EF) of ferromagnetic nanorods are substantially larger than those of weaker ferromagnetic nanorods, suggesting that the occupation of near-EF valence-band Co 3d states is important in determining the ferromagnetic behavior in Zn1−xCoxO nanorods.