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.

Automated summary

Interfacial inversion symmetry breaking can lead to electronic properties different from those of bulk materials. In this study, an artificial ferromagnetic quasi-two-dimensional electron gas (q2DEG) was achieved at the (111) interfaces of LaAlO3, EuTiO3, and SrTiO3, where the bulk quasioctahedral crystal field was reconfigured into a trigonal one. The q2DEG was formed through electron transfer to the EuTiO3 layers at the interface with LaAlO3, extending into the first layers of SrTiO3. Interestingly, polarized X-ray absorption spectroscopy revealed that the Eu-4f and Ti-3d magnetic moments exhibited ferromagnetic ordering and showed the same magnetic field dependence at low temperature. Additionally, the q2DEG displayed a significant in-plane orbital moment even at low magnetic fields (0.1 T), possibly due to Ti-3d electrons occupying bands with a predominant a1g orbital character.