Synthesis and characterization of ferromagnetic Zn1−xCoxO films

Abstract High-quality Zn 1− x Co x O (ZnCoO) thin films with different Co concentrations ( x =0−0.07) were synthesized on Al 2 O 3 substrates using a radio-frequency magnetron sputtering process. The structural, chemical, optical, and electrical properties of the films were characterized using various techniques. High-resolution X-ray diffraction measurements showed that the ZnCoO films had a c -oriented hexagonal wurtzite structure with no extra phases. The lattice constants of the films increased slightly with increasing the Co concentration ratio. X-ray photoelectron spectra show the incorporation of Co 2+ ions in the ZnO host without the formations of Co clusters. Hall measurements revealed that the films were n-type with a charge carrier density of ∼ 2.6 × 10 18 per cm 3 . A neutral-donor bound exciton peak (D 0 X) from all specimens was observed at 3.36 eV using photoluminescence measurements at 10 K. The physical and chemical properties of the films suggested that their ferromagnetic properties originated from a direct exchange interaction between magnetic Co ions.