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We report on the structural and magnetic properties of a cobalt-implanted ZnO film grown on a sapphire substrate. X-ray diffraction and transmission electron microscopy reveal the presence of a (1010)-oriented hexagonal Co phase in the Al2O3 sapphire substrate, but not in the ZnO film. Co clusters, with a diameter of is about 5-6 nm, form a Co rich layer in the substrate close to the ZnO/Al2O3 interface. Magnetization measurements indicate that there exist two different magnetic phases in the implanted region. One originates from the Co clusters in Al2O3, the other one belongs to a homogeneous ferromagnetic phase with a ferromagnetic Curie temperature far above room temperature and can be attributed to Co substitution on Zn sites in the ZnO layer. We have observed magnetic dichroism at the Co L2,3 and O K edges at room temperature as well as the multiplet structure in x-ray absorption spectra around the Co L3 edge, supporting the intrinsic nature of the observed ferromagnetism in Co-implanted ZnO film. The magnetic moment per substituted cobalt is found about 2.81 µB which is very close to the theoretical expected value of 3 µB/Co for Co 2+ in its high spin state.

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We have studied the structural, magnetic, and electronic properties of Co-implanted ZnO͑0001͒ films grown on Al 2 O 3 ͑1120͒ substrates for different implantation doses and over a wide temperature range. Strong room temperature ferromagnetism is observed with magnetic parameters depending on the cobalt implantation dose. A detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted ZnO films. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer and the second one is a superparamagnetic phase, which occurs due to the formation of metallic cobalt clusters in the Al 2 O 3 substrate. Using x-ray resonant magnetic scattering, the element specific magnetization of cobalt, oxygen, and Zn was investigated. Magnetic dichroism was observed at the Co L 2,3 edges as well as at the O K edge. In addition, the anomalous Hall effect is also observed, supporting the intrinsic nature of ferromagnetism in Co-implanted ZnO films.