Tuning the optical and magneto-optical properties in core-shell structured Fe@Ag nanoparticles

Magnetic nanoparticles (NPs) have attracted a great deal of attention due to their possible uses in many biomedical applications, such as targeted drug delivery, sensing, and ultra-sensitive disease detection. In this work, theoretical calculations based on optical absorption and magneto-optical (MO) properties in core-shell structured Fe@Ag NPs embedded in a polymethyl methacrylate (PMMA) host were investigated as a function of incident light wavelength. First, the optical absorption property of pure Ag NPs was investigated. For pure single spherical Ag nanoparticle with diameters in the range of 5-50 nm, the resonance absorption peak shows a slight redshift as the particle size increases. In terms of the optical absorption property for the two basic two-particle geometries of Ag NPs with varying Ag NPs interparticle distances ranging from 8-100 nm, when the particles were perpendicular to the direction propagation and parallel to the polarisation direction of an incident electric field, a blueshift of the absorption peak position was observed with increasing interparticle distance. On the other hand, a redshift of the absorption peak position with increasing interparticle distance was observed when the polarisation direction of the incident light was perpendicular to the particle axis. After coating plasmonic Ag on the Fe core called Fe@Ag core-shell NPs, the shifting and enhancement of the absorption and MO properties of Fe nanoparticles due to localised surface plasmon resonance excitation were observed to greatly exceed the calculated values for pure Fe NPs. The calculated results suggest that both interparticle distance and Ag shell thickness in a core-shell structured Fe@Ag NPs influence the tuning and enhancement of the spectra. These findings can be utilised as basic knowledge for the development of synthesis methods to obtain suitable Fe@Ag core-shell NPs for future applications.