Structural and magnetic properties of Fe-Al silica composites prepared 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 a-Fe. By changing the implantation order, 10–15 nm core–shell nanoparticles of a bcc Fe-based phase with a lattice 2.5% smaller than that of a-Fe are formed. The temperature dependence of the magnetization indicates a superparamagnetic behavior.