Structural and magnetic studies of Fe-implanted alpha-Al2O3

High fluence implantation of Fe in alpha-Al2O3 and post-implantation anneal ing leads to the formation of various phases in the near-surface region who se nature depend upon the annealing atmosphere and crystal orientation. The structural evolution of the near-surface region and the magnetic propertie s of samples oriented with either the c-axis or a-asis normal to the surfac e and annealed in oxidizing and reducing atmospheres were studied with glan cing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS)/channelling and vibrating sample mag netometry (VSM). The as-implanted samples contained metallic iron clusters in a damaged matrix. This matrix became amorphous for fluences of 2 x 10(17 ) Fe+/cm(2) and above. The annealing in oxidizing atmosphere of the samples with the a-axis normal to the surface leads to the formation of a mixed la ver containing alpha-Al2O3 and Fe2O3. The magnetization measurements indica te the presence of a large superparamagnetic contribution and a small ferro magnetic component. Annealing in a reducing atmosphere promotes the in-diff usion of iron and the magnetization decreases. A similar annealing of the s ample with c-axis normal to the surface induces coalescence of precipitates in a discontinuous buried film of metallic iron parallel to the c-plane wi th a strong ferromagnetic signal and a small superparamagnetic contribution . The magnetization increases with the annealing temperature. (C) 2000 Else vier Science S.A. All rights reserved.