Long-range magnetic ordering in metal-free materials

• Applicant: Professor Dr. Thomas Heine
• Subject Area: Theoretical Chemistry: Molecules, Materials, Surfaces ; Theoretical Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553623772

After predicting strong antiferromagnetic coupling of 144 meV across two triarylmethyl building blocks in their covalently coupled dimer (JACS 2023), and Stoner ferromagnetic aza-triangulene 2D polymers with Curie temperature of 260 K (arXiv 2023), it is timely to address metal-free magnetism in detail. We propose to explore metal-free materials with long-range magnetic orderings and Curie/Néel temperatures suitable for applications in short- and long-term information storage, electrical, and electromechanical devices, all of them potentially with biocompatibility. Metal-free magnetic ferro- and antiferromagnetic materials will become possible by linking stable radicaloid building blocks into covalently bound crystalline networks, and by developing graphene nanoribbons with distinct structural topology. We will develop metal-free one-, two- and three-dimensional crystals with robust long-range magnetic ordering, including metallic and semiconducting Stoner ferromagnets and antiferromagnetic Mott-Hubbard insulators. We will deeply investigate the nature of the magnetic couplings in these materials. As our preliminary work shows that magnetic ordering often occurs simultaneously with intriguing electronic features such as Dirac cones and flat bands, we will pay particular attention to understand the physical implications of these phenomena. On the computational side, we will use a hierarchical approach that includes high-level, including multi-reference, ab initio calculations for monomers, dimers and oligomers, (London dispersion corrected broken-symmetry) density-functional theory followed by the GW approach for high-quality band structures, tight-binding for the physical interpretation of the results, and Monte Carlo simulations based on a Heisenberg or Ising Hamiltonian to predict the long-range magnetic ordering. On a side note, our results will be useful for eliminating deficiencies of density-functionals, as many of them fail to describe metal-free magnetism (JCTC 2023). One-dimensional systems include graphene nanoribbons and one-dimensional polymers made of covalently coupled radicaloid building blocks. Two-dimensional polymers will be composed of one or two types of suitably coupled radicaloid monomers. Three-dimensional systems are based on covalent-organic frameworks, both in the form of layered materials and three-dimensional porous networks.

• DFG Programme: Reinhart Koselleck Projects