High-mobility spin-polarized two-dimensional electron gas at the interface of EuTiO₃/SrTiO₃ heterostructures

Spin polarization of two-dimensional electron gas (2DEG) at the interface of EuTiO₃/SrTiO₃(STO) heterostructures has been theoretical predicted and experimentally observed via x-ray magnetic circular dichroism and polarized x-ray absorption spectroscopy, which, however, is lack of magnetotransport evidence. Here, we report the fabrication of high-quality EuTiO₃/STO heterostructures by depositing antiferromagnetic insulating EuTiO₃ thin films onto STO substrates. Shubnikov-de Haas oscillation, Hall, and magnetoresistance (MR) measurements show that the interface is not only highly conducting, with electron mobility up to 5.5 × 10 3 cm²V⁻¹s⁻¹ at 1.8 K, but also shows low-field hysteretic MR effects. MR of ∼9% is observed at 1.8 K and 20 Oe, which is one order of magnitude higher than those observed in other spin-polarized 2DEG oxide systems. Moreover, the heterostructures show ferromagnetic hysteresis loops. These results demonstrate that the high-mobility 2DEG is spin polarized, whose origin is attributed to the interfacial Ti³⁺-3d states due to oxygen deficiency and the exchange interactions between interfacial Eu spins and itinerant Ti-3d electrons.