Room temperature ferromagnetism in Mn ion implanted epitaxial ZnO films

Epitaxial ZnO films of ∼450 nm thicknesses were grown by MOCVD on r-sapphire and doped by implantation of 200 keV Mn ions to a dose of 5 × 1016 ions/cm2. The structural, chemical, and magnetic properties of the films were investigated with X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), X-ray absorption spectroscopy (XAS) and SQUID magnetometry. XRD and RBS show both Mn-doped ZnO and pure ZnO epitaxial layers in the as-implanted film, which is ferromagnetic at 5 K but nonmagnetic at room temperature. For the as-implanted materials, only Mn2+ ions are observed with XAS. Post-implantation annealing partially recovers the lattice damage and redistributes Mn into the entire ZnO film; in addition, Mn2+ ions are converted to a mixture of Mn3+ and Mn4+, and ferromagnetism is now observed above 300 K. Our results show that ion implantation is a viable route for achieving room temperature ferromagnetism in epitaxial ZnO films. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)