Structural and magnetic properties of Fe-Al silica compositesprepared by sequential ion implantation

The nanostructural and magnetic properties of Fe-Al/SiO2 granular solids prepared by ion implantation have been investigated. A strong effect of the implantation order of the Fe and Al ions has been evidenced. By implanting first the Al ions and later Fe ions, 5-40 nm core-shell nanoparticles are formed with a magnetic behavior similar to that of Fe. The lattice parameter of the nanoparticles is consistent with that of the alpha-Fe. By changing the implantation order, 10-15 nm core-shell nanoparticles of a bee Fe-based phase with a lattice 2.5% smaller than that of alpha-Fe are formed. The temperature dependence of the magnetization indicates a superparamagnetic behavior.