Magneto-Optical Scattering from Nanometer-Scale Particles

We present calculations of the magneto-optical properties of magnetic particles with nanometer-scale dimensions. The scattering is calculated with the discrete dipole approximation (DDA). The DDA is a finite element approximation in which the particle is divided into a regular grid of radiating dipoles with grid spacing much smaller than the wavelength of incident radiation. The implementation of this approximation for gyrotropic (magneto-optical) media is discussed as well as the interpretation of the calculated scattering matrix. Calculations are performed for spherical particles, wires and collections of interacting particles. We also present experimental Faraday rotation spectra of magnetite nanoparticles in a polymer matrix. The data show a red shift of particular spectral features as a function of particle concentration. This is shown to be qualitatively consistent with model calculations which include interparticle interactions.