Ferromagnetic exchange, spin-orbit coupling and spiral magnetism at the LaAlO 3/SrTiO 3 interface

The electronic properties of the polar interface between insulating oxides is a subject of great interest. An exciting development is the observation of robust magnetism at the interface of two non-magnetic materials, LaAlO 3 (LAO) and SrTiO 3 (STO). Here we present a microscopic theory for the formation and interaction of local moments that depends on essential features of the LAO/STO interface. We show that correlation-induced moments arise owing to interfacial splitting of orbital degeneracy. We find that conduction electrons with a gate-tunable Rashba spin-orbit coupling mediate ferromagnetic exchange with a twist. We predict that the zero-field ground state is a long-wavelength spiral. Its evolution in an external field accounts semi-quantitatively for torque magnetometry data and describes qualitative aspects of the scanning superconducting quantum interference device measurements. We make several testable predictions for future experiments.