Magnetic properties of Fe+-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 T(a)le ss than or equal to 600 degrees C was very weak, and hard to saturate due t o the superparamagnetic effect. At T-a=800 degrees C, the saturation magnet ization increased significantly, but still much lower than that of bulk Fe. The coercivity of the films, either as-implanted or annealed, was much hig her than that of bulk Fe. No evident magnetic domain structure can be obser ved for the as-implanted and 600 degrees C annealed samples, which implied that the magnetic particles at lower temperatures were small and deeply emb edded in the film. During the annealing process at 800 degrees C, the impla nted Fe atoms gradually diffused outward with the formation of islands on t he film surface. These islands were demonstrated to be ferromagnetic. At th e initial stage of annealing (t(a)less than or equal to 1 h), all the islan ds 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 cou ld be observed in some larger islands, and no detectable magnetic particles remained in the films. (C) 2000 American Institute of Physics. [S0021-8979 (00)09317-8].