The 20 minutes website has also communicated on our article in The Conversation.

Des aimants légers et performants grâce à la chimie moléculaire…

Les aimants sont des matériaux présents dans de très nombreux objets de nos vies quotidiennes: ce sont par exemple des constituants essentiels de nos ordinateurs, des microphones, des moteurs électriques d’appareils ménagers ou même de turbines d’éoliennes. Pour certaines applications, comme dans les smartphones ou les satellites, ces aimants doivent être à la fois légers et de petite taille.

Les aimants sont généralement des solides constitués de métaux purs, d’oxydes métalliques ou d’alliages métalliques. Malgré leur utilisation intensive et leur énorme succès dans les applications technologiques, la production d’aimants pose des problèmes environnementaux et économiques. Certains éléments chimiques nécessaires à leur élaboration, comme les terres rares présents dans les aimants les plus puissants connus aujourd’hui, sont inégalement répartis sur la planète ou difficiles à isoler. De plus, la fabrication des aimants nécessite souvent des procédés réalisés à haute température qui consomment beaucoup d’énergie.

Afin de remédier à ces problèmes, les scientifiques essayent depuis environ 3 décennies de créer un nouveau type d’aimants en assemblant des molécules pour créer un édifice aux propriétés désirées. L’élaboration de tels assemblages moléculaires se fait à température ambiante, ce qui rend leur fabrication facile à reproduire et peu coûteuse. Cependant, il y a encore quelques mois, les performances des aimants moléculaires (température de fonctionnement, capacité d’attraction…) étaient encore très loin de celles des aimants conventionnels.

Récemment, dans une étude publiée dans Science, nous avons démontré qu’il est désormais possible d’obtenir des aimants moléculaires avec des caractéristiques comparables aux aimants conventionnels….

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Rodolphe Clérac, Research Director at the Centre de Recherche Paul and head of the “Molecular Materials & Magnetism” team, received the 2021 Silver Medal from the CNRS. In 2000, he joined the IUT of Bordeaux 1 and the Centre de Recherche Paul Pascal, as an associate professor. He began his career focusing on the physical properties of fullerene salts and new molecular materials. In 2001, he brought together a new research team around molecular magnetic materials and introduced coordination chemistry at the Centre de Recherche Paul Pascal.

^{Photo © Philippe Labeguerie}

In 2002, he discovered the first single-chain magnets, which opened up a new research field in molecular magnetism. His work then focused on these new one-dimensional magnets, the organization of molecule-magnets into coordination networks and he widened his researches towards bi- and tri-stable molecule-based systems with intramolecular electron transfer or spin conversion in solution, in the solid state or liquid crystal phases. In 2008, he joined the CNRS becoming a full-time researcher, and then in 2013, he was promoted to research director. In 2020, he developed a new post-synthetic approach and obtain the first molecular magnets operating up to 242°C with a high coercivity at room temperature. This synthetic strategy offers broad prospects for the preparation of a new generation of lightweight magnets at high temperature. His projects are currently directed towards the synthesis of new multifunctional molecule-based materials containing redox-active sites in order to obtain high-performance magnets also possessing high electrical conduction, photoactivity or porosity allowing selective gas absorption.

Rodolphe Clérac is author and co-author of over 500 publications and has presented over 130 invited lectures. He was elected in 2019 to the European Academy of Sciences and in 2020 to the Academia Europaea. In 2014, he became a junior distinguished member of the Société Chimique de France and received various awards including in 2017 the France-Berkeley Fund Award, in 2014 the National Chinese Award for the “1000 Talents Program” and in 2009 the Young Researcher Award of the Division de Chimie Physique de la Société Chimique de France.

Contact: Rodolphe Clérac
Centre de Recherche Paul Pascal, UMR CNRS 5031
“Molecular Materials & Magnetism” team
115 Avenue du Dr. A. Schweitzer, 33600 Pessac, FRANCE
Phone: +33 (0) 5 56 84 56 50

Towards next-generation molecule-based magnets

Magnets are to be found everywhere in our daily lives, whether in satellites, telephones or on fridge doors. However, they are made up of heavy inorganic materials whose component elements are, in some cases, of limited availability.

Now, researchers from the CNRS, the University of Bordeaux and the ESRF (European Synchrotron Radiation Facility in Grenoble) have developed a new lightweight molecule-based magnet, produced at low temperatures, and exhibiting unprecedented magnetic properties. This compound, derived from coordination chemistry, contains chromium, an abundant metal, and inexpensive organic molecules.  This is the first molecule-based magnet that exhibits a ‘memory effect’ (i.e. it is capable of maintaining one of its two magnetic states) up to a temperature of 240°C. This effect is measured by what is known as a coercive field, which is 25 times higher at room temperature for this novel material than for the most efficient of its molecule-based predecessors.  This property therefore compares well with that of certain purely inorganic commercial magnets. The discovery, published on 30 October in Science, opens up highly promising prospects, which could lead to next-generation magnets complementary to current systems.

Reference & authors: P. Perlepe, I. Oyarzabal, A. Mailman, M. Yquel, M. Platunov, I. Dovgaliuk, M. Rouzières, P. Négrier, D. Mondieig, E. A. Suturina, M.A. Dourges, S. Bonhommeau, R. A. Musgrave, K. S. Pedersen, D. Chernyshov, F. Wilhelm, A. Rogalev, C. Mathonière, R. Clérac, “Metal-organic magnets with large coercivity and ordering temperatures up to 242°C”, Science, Vol. 370, Issue 6516, pp. 587-592, (2020) – 10.1126/science.abb3861 – Abstract – Reprint – Full text

Online comments and publications

Acknowledgments: This work was supported by the University of Bordeaux, the Région Nouvelle Aquitaine, Quantum Matter Bordeaux, the Basque Government, the University of the Basque Country, the Villum Fonden, the University of Jyväskylä, the Academy of Finland, the Centre National de la Recherche Scientifique (CNRS) and the ESRF-The European Synchrotron.

Contact: clerac@crpp-bordeaux.cnrs.fr

This study reports the first transition metal compounds featuring mixed fluoride–cyanide ligands. A significant enhancement of the magnetic anisotropy, as compared to the pure fluoride ligated compounds, is demonstrated by combined analysis of high-field electron paramagnetic resonance (HF-EPR) spectroscopy and magnetization measurements.

What did scientists discover?

This study reports the first transition metal molecules featuring both fluorine and cyanide ligands (see “branches” attached to the metal atom (M) in the molecules at the top of the figure). A strong and significant enhancement of the non-uniformity of the magnetism, the “magnetic anisotropy” for the trans-[Re^IVF4(CN)₂]²– complex (shown in the upper right) was discovered by combined high-field magnetization and electron paramagnetic resonance (EPR) spectroscopy (see lower Figure).

Why is this important?

This research highlights an efficient new strategy for synthesizing molecular building blocks based on heavier transition metals that feature relatively large magnetic moments and very strong magnetic anisotropy. Such building blocks may form the basis for future high-performance magnetic materials used in high-density information storage applications.

Read more on MagLab website:

https://nationalmaglab.org/user-facilities/emr/emr-publications/highlights-emr/molecular-magnetic-building-blocks