Giant orbital magnetic moments in two-dimensional crystals

In this thesis, we investigate the importance of considering the atomic orbital magnetic moments when characterizing the electronic ground state of two-dimensional magnets. First, the PAW-ACA method for calculating atomic orbital magnetic moments is derived and benchmarked on known three-dimensional crystals. Afterward, the PAW-ACA method is applied to many different magnetic two-dimensional crystals in two different high-throughput materials discovery studies. For two-dimensional crystals with large orbital magnetic moments, i.e. FePS₃ and VI₃, we find that obtaining accurate electronic ground states requires the addition of self-consistent spin–orbit interactions as well as a Hubbard penalty at the magnetic atom to the Kohn-Sham Hamiltonian. We also find that failing to properly take into account the atomic orbital moments may lead to severe underestimations of the magnetic anisotropy and thus the critical temperature. Lastly, by using the octahedral crystal field model, we find that this severe underestimation of the orbital magnetic moments occurs not just FePS₃ and VI₃, but for many other materials with octahedrally coordinated ligands. We conclude by emphasizing the importance of accurately estimating the atomic orbital magnetic moments of a given material when trying to determine the critical temperature of said material.