Growth and magnetic properties of sol-gel derived Co-doped ZnO thin film

Zn_1-xCo_xO films were grown on glass by sol-gel spin coating process. A homogeneous and stable Zn_1-xCo_xO sol was prepared by dissolving zinc acetate dihydrate, cobalt acetate tetrahydrate and aluminum chloride hexahydrate as solutes in solution of isopropanol and monoethanolamine. The films were postheated and vacuum annealed, and investigated for c-axis preferred orientation and electromagnetic properties. Zn_1-xCo_xO films with different Co concentrations were oriented well along the c-axis, especially the Zn_1-xCo_xO film with 10% Co (atom fraction) was highly c-axis oriented. The transmittance spectra show that Zn_1-xCo_xO films occur d-d transition and sp-d exchange interaction between Co²⁺ ions. The electric resistivity of the films at 10% Co had the lowest value because the crystallite size became largest and the crystallinity of the c-axis was improved. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster was formed, and the ferromagnetism at room temperature appeared. The characteristics of the electric resistivity and room temperature ferromagnetism of sol-gel derived Zn_1-xCo_xO films suggest a potential application of dilute magnetic semiconductor devices.