Discrete dipole approximation for magneto-optical scattering calculations.

Magneto-optical spectra (Faraday effect) for nanometer-scale particles and collections of particles are calculated using a modification of the discrete dipole approximation (DDA). The approximation is used as a finite-element method for non-spherical particles whose dimensions are on the order of or smaller than the incident light wavelength, lambda. Also, we use the approximation to calculate scattering from arrangements of spherical nanoparticles with diameters << lambda. We propose that for scattering from subwavelength magnetic particles, the specific Faraday rotation should be defined as the difference in optical extinction for left- and right-circularly polarized light. We apply the model to calculations of Faraday rotation from magnetite nanowires as well as a binary (two-component) nanoparticle arrangement. Enhancements in Faraday rotation are predicted for composites containing both noble metal and ferrite nanoparticles.