Magnetic properties of [formula omitted]-implanted silica films after post-implantation annealing

Magnetic properties of Fe-implanted silica films after different annealing processes were studied. The magnetization of the samples annealed at [formula omitted] was very weak, and hard to saturate due to the superparamagnetic effect. At [formula omitted] the saturation magnetization increased significantly, but still much lower than that of bulk Fe. The coercivity of the films, either as-implanted or annealed, was much higher than that of bulk Fe. No evident magnetic domain structure can be observed for the as-implanted and 600 °C annealed samples, which implied that the magnetic particles at lower temperatures were small and deeply embedded in the film. During the annealing process at 800 °C, the implanted Fe atoms gradually diffused outward with the formation of islands on the film surface. These islands were demonstrated to be ferromagnetic. At the initial stage of annealing [formula omitted] all the islands were of a single-domain magnetic structure. Besides these islands, some embedded magnetic particles could also be detected. When the annealing time was prolonged to 2 h, double-domain or multidomain magnetic structures could be observed in some larger islands, and no detectable magnetic particles remained in the films.