  A large nonlinear magneto-optical effect is observed in a non-centrosymmetric
Fe/AlGaAs (001) heterostructure. This effect is a direct consequence of
interference between second-harmonic optical waves of magnetic and
crystallographic origin, generated at ferromagnetic Fe interface and bulk
AlGaAs, respectively. The longitudinal nonlinear Kerr rotation is measured to
be 1.6 degrees along the [1-10] hard axis, about two orders of magnitude
stronger than the linear equivalent. The rotational second-harmonic signal
shows large magnetic contrast along all the in-plane directions, demonstrating
a high sensitivity to the magnetization of an anisotropic interface in the
longitudinal geometry.
