Extraction of Backscattering and Absorption Coefficients of Magnetite Nanosphere Composites from Light-Scattering Measurements: Implications for Optomagnetic Sensing

Interaction of light with magnetic nanoparticles, dispersed in solution or embedded in other materials, is of major interest in a range of applications, one example being optomagnetic sensors. In applied research, light absorption and scattering of nanoparticle composites are often quantified by the Kubelka-Munk two-flux radiative transfer model. In this paper, we synthesized magnetite (Fe3O4) nanospheres with different diameters and encapsulated them into a polymer matrix. Their spectral transmittance and reflectance were investigated by spectrophotometry, together with measurements of angle-resolved scattering in the forward and backward hemispheres. The measured angular distribution was applied to approximate the scattering-phase function inside the film, which could be well described by the revised Reynolds-McCormick model. The backscattering and absorption coefficients were derived by inversion of the Kubelka-Munk relations, using the interface reflectances obtained from angle-dependent measurements. We present detailed optical properties for samples with various particle concentrations and scattering layer thicknesses, consisting of the magnetite and polymer composites. The absorption and backscattering coefficients for particles of diameter 458 nm showed qualitative agreement with single-scattering Mie calculations. The optical properties of composites with smaller particles might be influenced by an oxidized Fe3O4-like surface layer. The present approach can be used to study different kinds of magnetic nanoparticle clusters, dispersed in a supporting medium, and thus provide optical parameters of relevance for interpreting results of optomagnetic sensing experiments.