Optical properties of L10 FePt nanoparticles dispersed in a C matrix

Abstract

Optical properties of L10 FePt nanoparticles dispersed in a C matrix have been studied by using an approach combining spectroscopic ellipsometry and intensity transmission. Dielectric functions of FePt nanoparticles over a wavelength range of 380–1700 nm have been determined based on the Bruggeman effective medium approximation theory. Via analysis using the Drude–Lorentz model, the extracted optical properties provide electronic information of FePt nanoparticles. As compared with the thin film composed of larger grains, decrease of free electron absorption is observed in FePt nanoparticles, and this absorption decrease causes dielectric suppression in the near-IR photon energy range. And it can be due to the increased surface scattering and reduced unscreened plasma frequency in nanoparticles. On the other hand, two interband electronic transitions located at 0.7 and 1.0 eV are derived, which are in good agreement with the reported density of states of L10 FePt. In the present work, they show only a small dependence on FePt particle size. Such a study of optical properties of FePt nanoparticles is important for technological applications and fundamental physics.