  We show the existence of intrinsic localized spins in mesoscopic
high-mobility GaAs/AlGaAs heterostructures. Non-equilibrium transport
spectroscopy reveals a quasi-regular distribution of the spins, and indicates
that the spins interact indirectly via the conduction electrons. The
interaction between spins manifests in characteristic zero-bias anomaly near
the Fermi energy, and indicates gate voltage-controllable magnetic phases in
high-mobility heterostructures. To address this issue further, we have also
designed electrostatically tunable Hall devices, that allow a probing of Hall
characteristics at the active region of the mesoscopic devices. We show that
the zero field Hall coefficient has an anomalous contribution, which can be
attributed to scattering by the localized spins. The anomalous contribution can
be destroyed by an increase in temperature, source drain bias, or field range.
