Size dependent hcp-to-fcc transition temperature in Co nanoclusters obtained by ion implantation in silica

In this work we present in situ investigations on the increase of the hcp-to-fcc transition temperature for Co with respect to the bulk value (420 degrees C) when nanoclusters are considered. Starting from Co:SiO2 composites obtained by ion implantation with average Co cluster size of about 5 nm, a transition temperature between 800 degrees C and 900 degrees C is found upon thermal annealing in vacuum by in situ transmission electron microscopy. Preliminary results on electron irradiation to promote the transition at lower temperatures are presented.