Microstructure, magnetic, and optical properties of sputtered Mn-doped ZnO films with high-temperature ferromagnetism

The microstructure, magnetic, and optical properties of Mn-doped ZnO films have been examined. It has been found that Mn doping could improve the growth of ZnO (002) orientation without Mn oxide formation. All the films are ferromagnetic with a Curie temperature of above 350 K. The ferromagnetism comes from the ferromagnetic interaction activated by oxygen vacancies between the Mn ions that replace Zn ions, but not from Mn oxide impurities. At an atomic fraction of 2.2% Mn, the average moment per Mn ion reaches a maximum of 0.55 mu(B). With the further increase of Mn atomic fraction, the average moment per Mn ion decreases because the antiferromagnetic energy is lower than the ferromagnetic one due to the reduced distance between the adjacent Mn ions. Meanwhile, the optical band gap value increases from 3.120 to 3.162 eV with the increase of Mn atomic fraction from 0% to 7.5%. (c) 2007 American Institute of Physics.