  In this work, we are concerned with the mathematical modeling of the
electromagnetic (EM) scattering by arbitrarily shaped non-magnetic
nanoparticles with high refractive indices. When illuminated by visible light,
such particles can exhibit a very strong isotropic magnetic response, resulting
from the coupling of the incident wave with the circular displacement currents
of the EM fields. The main aim of this work is to mathematically illustrate
this phenomenon. We shall first introduce the EM scattering resolvent and the
concept of dielectric subwavelength resonances. Then we derive the a priori
estimates for the subwavelength resonances and the associated resonant modes.
We also show the existence of resonances and obtain their asymptotic expansions
in terms of the small particle size and the high contrast parameter. After
that, we investigate the enhancement of the scattering amplitude and the cross
sections when the resonances occur. In doing so, we develop a novel multipole
radiation framework that directly separates the electric and magnetic multipole
moments and allows us to clearly see their orders of magnitude and blow--up
rates. We prove that at the dielectric subwavelength resonant frequencies, the
nanoparticles with high refractive indices behave like the sum of the electric
dipole and the resonant magnetic dipole. Some explicit calculations and
numerical experiments are also provided to validate our general results and
formulas.
