The dopant concentration and annealing temperature dependence of ferromagnetism in Co-doped ZnO thin films

A series of Zn_1−xCo_xO thin films with the atomic fraction, x, in the range of 0.03–0.10 were deposited on glass substrates at room temperature by magnetron co-sputtering technique and subsequently coupled with the post-annealing treatment for half hour at different temperatures (350 °C and 500 °C) under vacuum. A systematic study was done on the structural, optical and magnetic properties of Zn_1−xCo_xO thin films as a function of Co concentration and annealing temperature. X-ray diffraction and UV–vis spectroscopy results indicated that there are not any secondary phases and Co²⁺ substituted for Zn²⁺ of ZnO host. Magnetic hysteresis loops were observed at room temperature, indicating that both the as-deposited samples and the annealed ones exhibit the room temperature ferromagnetism. It was also found that the magnetic saturation moment per Co atom decreases with increasing Co concentration, while the post-annealing treatment can enhance the magnetic moment of the films effectively.