Colloidal cobalt-doped ZnO nanorods:: Synthesis, structural, and magnetic properties

The synthesis of ZnO:Co nanorods in alcoholic solutions and their structural, optical, and magnetic properties are presented. One-dimensional growth is achieved by careful control over the precursor addition and with the aid of ethylene diamine as a ligand. The nanorods are single-crystalline and show growth into the [0001] direction. They exhibit diameters of about 20 nm and lengths up to 150 nm. Using (HR)TEM, EDX, and XANES, we prove the incorporation of Co cations on Zn lattice sites. SQUID and XMCD measurements at cryogenic temperatures show paramagnetic behavior of the doped nanorods. Apparently, there are too few donor electrons to mediate ferromagnetic coupling in the highly crystalline nanorods compared to defect-rich spherical nanoparticles.