Scientists manage to chemically adjust the electronic properties of new layered materials

As part of an international collaboration, scientists from the Centre de Recherche Paul Pascal, the Institut de Chimie de la Matière Condensée de Bordeaux (CNRS/University of Bordeaux) and the ESRF have shown how to chemically adjust the electronic structure of a layered metal-organic material to control its physical properties, such as electrical conduction and magnetism. This work, published in the journal Nature Communications, paves the way for the design of a new generation of conducting, and potentially superconducting, molecule-based materials.

Molecule-based components proposed for integration into our miniaturized electronic equipment must possess perfectly controlled magnetic and electrical conduction properties. Their ability to be semiconductors, conductors or even insulators, while exhibiting remarkable magnetic properties, makes them very good candidates for integration into future devices for spintronic applications. This is why chemists and physicists are working together to understand the precise role of physicochemical parameters at the origin of the electrical conduction and magnetic properties. With this aim, scientists from more than ten institutions worldwide, led by the Centre de Recherche Paul Pascal (CNRS/University of Bordeaux), studied the coordination materials MCl2(pyrazine)2 (see Figure). These coordination polymers have the particularity to display a layered (2D) structure and to possess strong metal-ligand interactions, which exacerbate the targeted electronic properties. In this family of iso-structural materials, the scientists’ goal was to understand why the vanadium and titanium analogues are an antiferromagnetic insulator and a paramagnetic metal, respectively, while the chromium-based compound is a ferrimagnetic semiconductor.

By combining the analyses of electrical conductivity, magnetoresistance, magnetic properties, specific heat, and density functional calculations (DFT) with the X-ray absorption spectroscopy carried out at the ESRF’s ID12 beamline, the international research teams managed to get a complete picture of the scientific case. “The ID12 beamline is where all questions regarding local magnetic and orbital moments, oxidation state and electronic structures get answers! And if we cannot get an answer right away, we have the chance to modify the experimental setup on the beamline or to imagine new materials to complete the story. What a luxury to work in this unique world-class facility and with its scientists”, explains Rodolphe Clérac, CNRS researcher at the Centre de Recherche Paul Pascal and main corresponding author of the publication. In this published work, the authors show that in the case of vanadium, the pyrazine ligands simply mediate strong interactions between the V(II) spins that remain localized on each metal centre. On the other hand, for titanium, they highlight the transfer of an electron between the Ti(II) ion and the two pyrazine ligands, during the synthesis. For this reason, TiCl2(pyrazine)2 then displays a metallic behavior (a strongly correlated Fermi liquid state), and even presents the highest electrical conductivity ever observed among coordination solids based on octahedrally coordinated metal ions.

“We have a long-standing collaboration with the research team at the Centre de Recherche Paul Pascal and this work is another example of excellent fundamental science combining their methodology with the unique ESRF’s facilities”, says Andrei Rogalev, scientist in charge of ID12.

This work shows how the choice of the metal ion M in a series of iso-structural materials, allows to finely control their physical properties, and in particular their electrical conduction but also their magnetism. Rodolphe Clérac explains the implications of this finding in the long term: “Our results pave the way for the design of a new generation of metal-organic materials possessing metallic or even potentially superconducting properties”.

Structure of the MCl2(pyrazine)2 materials shown perpendicular (a) and parallel (b) to the 2D layers. Color code: V, dark green; Cl, green; N, blue; C, grey. @K. Pedersen & R. Clérac


Panagiota Perlepe, Itziar Oyarzabal, Laura Voigt, Mariusz Kubus, Daniel N. Woodruff, Sebastian E. Reyes-Lillo, Michael L. Aubrey, Philippe Négrier, Mathieu Rouzières, Fabrice Wilhelm, Andrei Rogalev, Jeffrey B. Neaton, Jeffrey R. Long, Corine Mathonière, Baptiste Vignolle, Kasper S. Pedersenet Rodolphe Clérac

From an antiferromagnetic insulator to a strongly correlated metal in square-lattice MCl2(pyrazine)2 coordination solids

Nature Communications 2022


Rodolphe Clérac, CNRS researcher at the CRPP

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