Ferromagnetic Quasi-Two-Dimensional Electron Gas with Trigonal Crystal Field Splitting

Interfacial inversion symmetry breaking gives rise to electronic properties that differ substantially from those of the bulk constituent materials. Here, we report on the realization of an artificial ferromagnetic quasi-two-dimensional electron gas (q2DEG) at the (111) interfaces between LaAlO3, EuTiO3, and SrTiO3 characterized by a reconstruction of the bulk quasioctahedral crystal field into a trigonal one. The q2DEG is created through a transfer of electrons to the EuTiO3 layers at the interface with LaAlO3, extending into the first layers of SrTiO3, as shown by an electron-energy-loss spectroscopy map of the titanium valence with atomic column resolution. Interestingly, polarized X-ray absorption spectroscopy shows that the Eu-4f and the Ti-3d magnetic moments order ferromagnetically and exhibit the same magnetic field dependence at low temperature. In addition, the q2DEG presents a sizable in -plane orbital moment even at low magnetic field (0.1 T) possibly related to Ti-3d electrons occupying bands with the main a1g orbital character. The results show an intriguing interplay between ferromagnetism, spin-orbit coupling, and trigonal crystal field splitting in the (111) LaAlO3/EuTiO3/SrTiO3 q2DEG.