Synthesis and characterization of ferromagnetic Zn1−xCoxO films

High-quality Zn1−xCoxO (ZnCoO) thin films with different Co concentrations (x=0−0.07) were synthesized on Al2O3 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 Co2+ 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 ∼2.6×1018∼2.6×1018 per cm3. A neutral-donor bound exciton peak (D0X) 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.

► High-quality ZnCoO film growth using RF sputtering process.
► ZnCoO films are sing crystals with no extra phases.
► XPS confirms the chemical valence state of Co2+.
► Hall measurements revealed n-type semiconductors.
► The ferromagnetic properties of the films are induced by the direct interaction between Co ions.