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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.
Originalsprache  englisch 

Aufsatznummer  195123 
Fachzeitschrift  Physical Review B 
Jahrgang  103 
Ausgabenummer  19 
DOIs  
Publikationsstatus  Veröffentlicht  2021 
ASJC Scopus subject areas
 Elektronische, optische und magnetische Materialien
 Physik der kondensierten Materie
Fields of Expertise
 Advanced Materials Science
Treatment code (Nähere Zuordnung)
 Theoretical
Kooperationen
 NAWI Graz
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FWF  TOPOMAT  Abinitio Zugänge zu topologischen Materiezuständen
1/11/14 → 31/10/22
Projekt: Foschungsprojekt