Influence of Vacuum Annealing on Structural, Optical, Electrical, and Magnetic Properties of Zn $_{0.94}$Co $_{0.05}$Al $_{0.01}$O Diluted Magnetic Semiconductor Thin Films

The Zn
_0.94
Co
_0.05
Al
_0.01
O diluted magnetic semiconductor (DMS) thin films were made by rf magnetron co-sputtering, and annealed in vacuum at 500°C (for 0, 20, 40, and 80 min, respectively). The films have a single ZnO wurtzite structure with -axis preferred orientations, without any segregated secondary phase, and Co
²⁺
ions substitute tetrahedrally coordinated Zn
²⁺
ions site. The as-grown film is insulating and in a state of tensile stress parallel to the c-axis. After annealing in vacuum, the films have tensile stresses parallel to the (002) plane, and become conductive; moreover, the carrier concentrations increase with increasing the annealing time. The as-grown film possesses the room-temperature ferromagnetism (RTFM) and the saturation magnetization (M
_s
) is 0.8 μ
_B
/Co. As the film is annealed in vacuum, the value of M
_s
is reduced first then enhanced with the increase of annealing time.