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TT: Fachverband Tiefe Temperaturen
TT 21: Electron Theory of Magnetism and Correlations (joint session MA/TT)
TT 21.10: Vortrag
Montag, 9. März 2026, 17:30–17:45, POT/0151
Transition metal dihalides: from band structure to magnetic properties — •Alexander Yaresko1, Sebastien Hadjadj2, and Maxim Ilyn2 — 1Max Planck Institute for Solid State Research, Stuttgart, Germany — 2Centro de Física de Materiales, Donostia-San Sebastián, Spain
Transition metal dihalides TX2 (T=Fe, Ni, X=Cl, Br) have recently attracted attention because of successful growth of monolayer-thick TX2 films on various substrates, such as Au or NbSe2, allowing to study 2D magnetism. We compare results of band structure calculations for bulk and monolayer FeX2 and NiX2. By mapping the total energies calculated for helical spin structures with various q to the Heisenberg model we show that the change of magnetic order within a layer from ferro- in NiCl2 to helimagnetic in NiBr2 can be explained by the increased strength of antiferromagnetic (AF) 3-rd neighbor exchange interaction J3 which competes with FM nearest neighbor J1. We found that inter-layer coupling J2c stabilizes FM order within a layer. Thus, one can expect stronger tendency to a helimagnetic state in a NiX2 monolayer.
In contrast to NiX2, J1 estimated from LDA+U spin-spiral calculations for FeX2 is weak but shows substantial dependence on the strength of the Coulomb repulsion U. In agreement with experimental findings, calculations including spin-orbit coupling result in appreciable easy axis anisotropy with Fe magnetic moments normal to layers.
We also discuss various microscopic contributions to intra- and inter-layer exchange interactions.
Keywords: exchange interaction; van der Waals magnet; band structure