Photonic anisotropic magnetoresistance in dense Co particle ensembles

In this Letter, we experimentally show that the amplitude and arrival time of the terahertz optical transmission through dense ensembles of subwavelength-size ferromagnetic particles is strongly dependent on the orientation of an externally applied magnetic field. The attenuation and delay have the same magnetic field orientation dependence as the electrical anisotropic magnetoresistance inherent to bulk ferromagnetic metals. We envision the application of this magnetic effect in terahertz photonic devices.