Co-deposition of FePt and CoPt nanoparticles on silicon dioxide

In this study, Fe₅₀Pt₅₀ and Co₅₀Pt₅₀ nanoparticles are prepared by electron beam evaporation by co-deposition on thermally oxidized silicon (100) substrates with a SiO₂ amorphous layer of 90 nm on top. The samples are deposited at a substrate temperature T_s ∼ 750°C and with a nominal thickness of the layer of 8.5 nm. Annealing of the samples is done at 750°C immediately after deposition. The structural and morphological properties are analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The compositional map of selected samples is obtained by electron energy loss spectroscopy (EELS) and the quantitative chemical characterization is performed by energy dispersion X-ray analysis. The magnetic properties of the nanoparticles are measured using a magneto optical Kerr effect magnetometer at room temperature. XRD patterns indicate that the as-deposited samples are in the cubic phase with a (111) texture. Increasing the annealing time results in the progressive crystallization of the Ll₀ ordered phase with a (111) texture and in the progressive magnetic hardening of the samples with the maximum coercivity of ∼ 7.4 kOe.