  We report a giant enhancement of the mid-infrared (MIR) magneto-optical
complex Kerr angle (polarization change of reflected light) in a variety of
materials grown on SiC. In epitaxially-grown multilayer graphene, the Kerr
angle is enhanced by a factor of 68, which is in good agreement with Kerr
signal modeling. Strong Kerr enhancement is also observed in Fe films grown on
SiC and Al-doped bulk SiC. Our experiments and modelling indicate that the
enhancement occurs at the high-energy edge of the SiC reststrahlen band where
the real component of the complex refractive index n passes through unity.
Furthermore, since the signal is greatly enhanced when n=1, the enhancement is
predicted to exist over the entire visible/infrared (IR) spectrum for a
free-standing film. We also predict similar giant enhancement in both Faraday
(transmission) and Kerr rotation for thin films on a metamaterial substrate
with refractive index n=-1. This work demonstrates that the substrate used in
MOKE measurements must be carefully chosen when investigating magneto-optical
materials with weak MOKE signals or when designing MOKE-based optoelectronic
devices.
