Projects per year
Abstract
We investigate the emergence of ferromagnetism in the twodimensional metal halide CoBr2, with a special focus on the role of electronic correlations. The calculated phonon spectrum shows that the system is thermo dynamically stable, unlike other Co halides. We apply two wellknown methods for the estimation of the Curie temperature. First, we do densityfunctional theory +U calculations to calculate exchange couplings, which are subsequently used in a classical Monte Carlo simulation of the resulting Ising spin model. The transition temperature calculated in this way is of the order of 100 K but shows a strong dependence on the choice of interaction parameters. Second, we apply dynamical meanfield theory to calculate the correlated electronic structure and estimate the transition temperature. This results in a similar estimate for a noticeable transition temperature of approximately 100 K, but without the strong dependence on the interaction parameters. The effect of electronelectron interactions are strongly orbital selective, with only moderate correlations in the three lowlying orbitals (one doublet plus one singlet) and strong correlations in the doublet at higher energy. This can be traced back to the electronic occupation in DMFT, with five electrons in the three lowlying orbitals and two electrons in the highenergy doublet, making the latter one half filled. Nevertheless, the overall spectral gap is governed by the small gap originating from the lowlying doublet+singlet orbitals, which changes very weakly with interaction U . In that sense, the system is close to a Mott metaltoinsulator transition, which was shown previously to be a hot spot for strong magnetism.
Original language  English 

Article number  195123 
Journal  Physical Review B 
Volume  103 
Issue number  19 
DOIs  
Publication status  Published  2021 
ASJC Scopus subject areas
 Electronic, Optical and Magnetic Materials
 Condensed Matter Physics
Fields of Expertise
 Advanced Materials Science
Treatment code (Nähere Zuordnung)
 Theoretical
Cooperations
 NAWI Graz
Projects
 1 Finished

FWF  TOPOMAT  Topological states of matter from first principles
1/11/14 → 31/10/22
Project: Research project