  Quantum corrections to electrical resistance can serve as sensitive probes of
the magnetic landscape of a material. For example, interference between
time-reversed electron paths gives rise to weak localization effects, which can
provide information about the coupling between spins and orbital motion, while
the Kondo effect is sensitive to the presence of spin impurities. Here we use
low-temperature magnetotransport measurements to reveal a transition from weak
antilocalization (WAL) to Kondo scattering in the quasi-two-dimensional
electron gas formed at the interface between SrTiO$_3$ and the Mott insulator
NdTiO$_3$. This transition occurs as the thickness of the NdTiO$_3$ layer is
increased. Analysis of the Kondo scattering and WAL points to the presence of
atomic-scale magnetic impurities coexisting with extended magnetic regions that
affect transport via a strong magnetic exchange interaction. This leads to
distinct magnetoresistance behaviors that can serve as a sensitive probe of
magnetic properties in two dimensions.
