Structural and magnetic properties of cadmium oxides with different annealing temperatures

A series of cadmium oxide samples (CdOs) were synthesized by thermal treatment method with various annealing temperatures (TA = 500 degrees C - 900 degrees C). All samples crystallize in a pure cubic structure with Fm3m symmetry. The crystallite size, lattice parameter and volume change slightly with TA, and show an unexpected inflection point for the sample with TA = 800 degrees C (CdO-800), while the average particle size increases monotonically from -0.4 mu m to -3.0 mu m. Distinct ferromagnetic features accompanied by diamagnetic and/or paramagnetic phases were detected. The XPS data indicate the valence of cadmium and oxygen vacancy concentration varies with TA, which are responsible for the ferromagnetic origin in CdOs. CdO-800 shows the maximum magnetization, significant coercive force and residual magnetization. Oxygen vacancy plays a crucial role in the ferromagnetic performance, which can be effectively controlled by changing the sintering temperature. This work claims new characteristics for CdO besides optical and semi-conducting, which may be important in the preparation and possible applications for CdO dilute magnetic semiconductors.