Title:	Strong electronic correlations and magnetism in systems containing transition metals and lanthanides
DNr:	NAISS 2023/5-540
Project Type:	NAISS Medium Compute
Principal Investigator:	Igor Dimarco <igor.dimarco@physics.uu.se>
Affiliation:	Uppsala universitet
Duration:	2024-01-01 – 2025-01-01
Classification:	10304 10407
Homepage:	http://fplmto-rspt.org/
Keywords:

Abstract

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. In a recent project [Comp. Mater. 8, 1 (2022)], we demonstrated that (111)-oriented superlattices of LaMnO3 and SrMnO3 exhibit a peculiar ferromagnetism, not driven by interfacial phenomena. Varying thickness was found to affect electronic, magnetic and structural properties all together, which can be used to obtain a phase with an emergent separation between Jahn-Teller and breathing distortions [ arXiv 2311.01081]. Next, we intend to analyse magnetism more in detail, by mapping the electronic structure problem onto an effective Heisenberg model, to be solved via atomistic spin-dynamics simulations. This analysis would offer a more direct connection to the experiment, which is important for understanding the applicability of these superlattices in technology as well as for connecting to experimental characterization. In this regard, we established a collaboration with the experimental group of Prof. V. Lazarov, at the University of York, where synthesis will be attempted. Further work on oxides will be focused on EuTiO3, in various phases. After having investigated the electronic and magnetic properties of the bulk at equilibrium, we now intend to analyse the response to applied strain. Our aim is to identify the competing exchange mechanisms and to understand how their balance may be altered via external stimuli. This insight will be useful to investigate the LaAlO3|EuTiO3|SrTiO3 heterostructure, which has been suggested to host a magnetic quasi two-dimensional electron gas (q2DEG) [Quantum Mater. 7, 1 (2022)]. By combining electronic structure calculations with atomistic spin-dynamics simulations, we intend to clarify the origin of the long range order, the relation between ordering temperature and EuTiO3 thickness, and the role played by the Ti-3d states. The calculation of the X-ray absorption spectra and their comparison with available experimental data will be useful to understand how the nominal valence of Eu (in different ionization states) affects the q2DEG, emphasizing the role played by vacancies and impurities. Our second line of research is focused on materials with anisotropic magnetic coupling that may exhibit strong electronic correlations. We are especially interested in Fe3Sn, which is a strong ferromagnet with a high Curie temperature that holds potential as a permanent magnet. To this aim, one needs to rotate the easy axis from in-plane to out-of-plane, which has been attempted via doping at both Fe/Sn sites. The triangular Kagome lattice, as well as the presence of Sn, suggest interesting effects in electronic and magnetic properties, including a significant Dzyaloshinskii-Moriya interaction. In related materials, flatbands near the Fermi level have been reported, resulting in a large effective mass and exotic transport [Nat. Mater. 19, 163 (2019); PRL 121, 096401 (2018)]. To clarify these issues, we will perform DFT and DFT+DMFT calculations, evaluate magnetic properties and inter-atomic exchange coupling, with and without relativistic effects.