OBSERVATION OF A RAPID AMORPHIZATION REACTION

We have observed a rapid amorphization reaction at ambient temperature in the Gd/Co system by employing grazing incidence x-ray scattering. We find that a 135 angstrom crystalline Gd film is amorphized in less than 30 min by deposition of Co. We postulate that the rapidity of the reaction is due to surface diffusion of Co atoms after deposition to fast diffusion sites such as grain boundaries in the Gd film. Once the interfacial region has been amorphized these fast diffusion paths are sealed off from the surface, rapid diffusion of Co into the Gd crystalline layer is prevented, and the amorphization reaction stops.