Superparamagnetic and ferromagnetic CoPt nanoparticles deposited on silicon dioxide

Co50Pt50 nanoparticles were co-deposited on thermally oxidized Si substrates by electron beam evaporation, at a substrate temperature between RT and 750 deg. C. The co-deposition led to formation of nanoparticles which exhibit a mean diameter between 2 and 20 nm depending on the nominal thickness of the layer and on the substrate temperature. Different processing conditions resulted in different structural and morphological properties of the samples, which led to superparamagnetic and ferromagnetic behaviours. The post-annealing treatment of the CoPt nano-grains, performed in-situ soon after the deposition in the crystallization of the L10 ordered phase and consequently in the progressive magnetic hardening of the samples with a maximum coercivity of ∼7.4 kOe