Extrinsic origin of ferromagnetism in ZnO and Zn_(0.9)Co_(0.1)O magnetic semiconductor films prepared by sol-gel technique

摘要

We report on the origin of ferromagnetism in ZnO and Co-doped ZnO magnetic semiconductor films prepared by sol-gel technique on Si(100) and SiO_2 substrates. X-ray diffraction measurements have shown that ZnO and Co-doped ZnO have the expected wurtzite structure and a preferential orientation along the c axis. Optical transmittance measurements revealed that Co is incorporated into the lattice, as Co~(2+) substituting Zn~(2+) ions. Magnetization measurements have shown room-temperature ferromagnetism for both ZnO and ZnO:Co films. After annealing, the magnetization curves recorded on free substrates show the same ferromagnetic behavior as the ZnO:Co film indicating that the ferromagnetism is extrinsic and due to external pollution.