Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 55: Correlated Electrons: Low-Dimensional Systems -Materials 2
TT 55.4: Vortrag
Donnerstag, 14. März 2013, 10:15–10:30, H21
Magnetism of CuX2 frustrated chains (X = F, Cl, Br): the role of covalency — •Stefan Lebernegg1, Miriam Schmitt1, Alexander Tsirlin1,2, Oleg Janson1, and Helge Rosner1 — 1MPI Chemical Physics of Solids, Dresden, Germany — 2National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
Periodic and cluster DFT calculations, including DFT+U and hybrids, are applied to study magnetostructural correlations in spin-1/2 frustrated chain compounds: CuCl2, CuBr2, and a fictitious chain structure of CuF2. The nearest-neighbor and second-neighbor exchange integrals, J1 and J2, are evaluated as a function of the Cu–X–Cu bridging angle θ in the physically relevant range 80–110∘. The ionic CuF2 exhibits ferromagnetic coupling only for θ≤100∘, according to the Goodenough-Kanamori-Anderson rules. However, both CuCl2 and CuBr2 feature ferromagnetic J1 in the whole angular range studied. This surprising behavior is ascribed to the increased covalency in the Cl and Br compounds, which amplifies the contribution from Hund’s exchange on the ligand atoms and renders J1 ferromagnetic. At the same time, the larger spatial extent of X orbitals enhances the antiferromagnetic J2, which is realized via the long-range Cu–X–X–Cu paths. Both, periodic and cluster approaches supply a consistent description of the magnetic behavior which is in good agreement with the experimental data for CuCl2 and CuBr2. Thus, owing to their simplicity, cluster calculations have excellent potential to study magnetic correlations in more involved spin lattices, especially making parameter-free quantum-chemical methods computationally feasible.