Structure and thermal stability of Au-Fe alloy nanoclusters formed by sequential ion implantation in silica

Sequential ion implantation of Au and Fe ions has been performed in silica. Despite the fact that the two species are not miscible in the bulk, structural characterizations show that the nanoparticles produced are a Au-Fe alloy. The crystalline structure of the nanoparticles is fcc with a lattice parameter of 0.395 nm. The nanocomposite is ferromagnetic at 3 K, with a magnetic moment per Fe atom equal to 1.4 mu(B) and it shows a hysteresis loop with a coercive field of 24 mTorr. Due to alloying, the optical absorption spectrum does not exhibit the typical surface plasmon resonance of gold nanoparticles. The sample exhibits a change of its optical and structural properties when is annealed at 600 degrees C.