Structural and magnetic studies of Fe-implanted α-Al2O3

High fluence implantation of Fe in α-Al2O3 and post-implantation annealing leads to the formation of various phases in the near-surface region whose nature depend upon the annealing atmosphere and crystal orientation. The structural evolution of the near-surface region and the magnetic properties of samples oriented with either the c-axis or a-axis normal to the surface and annealed in oxidizing and reducing atmospheres were studied with glancing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS)/channelling and vibrating sample magnetometry (VSM). The as-implanted samples contained metallic iron clusters in a damaged matrix. This matrix became amorphous for fluences of 2×1017 Fe+/cm2 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 layer containing α-Al2O3 and Fe2O3. The magnetization measurements indicate the presence of a large superparamagnetic contribution and a small ferromagnetic component. Annealing in a reducing atmosphere promotes the in-diffusion of iron and the magnetization decreases. A similar annealing of the sample with c-axis normal to the surface induces coalescence of precipitates in a discontinuous buried film of metallic iron parallel to the c-plane with a strong ferromagnetic signal and a small superparamagnetic contribution. The magnetization increases with the annealing temperature.