In this project, we plan to use density functional theory (DFT) and its combination with dynamical mean field theory (DMFT) to pursue two major lines of research.
Our first line of research is focused on oxide heterostructures of various compositions. In a recent project [npj Comp. Mater. 8, 1 (2022)], we demonstrated that (111)-oriented superlattices of LaMnO3 and SrMnO3 exhibit a very peculiar ferromagnetism. This ferromagnetism is interfacially-driven for the (001) orientation, but arises from a proper bulk-like phase transition for the (111) orientation. As a result, these materials are more robust against thermal fluctuations and therefore may become components of spintronic devices. We intend to perform DFT and DMFT calculations to understand how the physical properties depend on compositional parameters such as thickness and component ratio. Moreover, we intend to investigate (001)-oriented superlattices of SrMnO3 and NdMnO3, which were found in experiment to exhibit an interesting series of metal-insulator transitions with respect to their thickness. Relevant experimental data have been provided to us by the group of Prof. S. Middey at the Indian Institute of Science of Bengaluru, India. Our joint theoretical and experimental efforts will likely clarify what mechanisms drive the phase transitions. Finally, we also intend to unveil the physical mechanisms driving the peculiar magnetic properties observed in bulk and surface EuTiO3. Particularly interesting are sandwiched interfaces, which may lead to the formation of a magnetic quasi two-dimensional electron gas, as in the case of LaAlO3|EuTiO3|SrTiO3.
Our second line of research is focused on the magnetism of systems containing lanthanide elements. We recently completed the implementation of a method to extract the anisotropic contributions to the inter-atomic exchange interaction [PRB 102, 115162 (2020)]. The anti-symmetric part, usually referred to as the Dzyaloshinskii-Moriya interaction, is important for several properties, as e.g. the phase diagram of multiferroics and the texture of skyrmions. We have almost completed a first investigation of these interactions in bulk lanthanide metals. We now intend to proceed to the analysis of their surfaces, where an increase is expected due to the reduced symmetry. The Dzyaloshinskii-Moriya interaction can also become very large in pyrochlore lanthanide-based iridates, where it competes with the underlying super-exchange. Other materials where the anisotropic contributions to the inter-atomic exchange are expected to be important are the lanthanide-based double-perovskites. These systems were proposed as candidates for the realization of spin liquids and we intend to clarify this issue with an adequate theoretical investigation. Finally, we intend to focus also on the intra-atomic exchange coupling, which drives the formation of the magnetic order in many lanthanide-based systems. We recently formulated a new method to evaluate anisotropic contributions to the intra-atomic exchange [yet unpublished]. We intend to apply this new method to lanthanide adatoms deposited on graphene, whose isotropic contribution was studied by us a couple of years ago [PRX 10, 031054 (2020)].