Data storage

Tetranuclear rare earth metal complexes with giant spin

Credit: Angewandte Chemie

Magnets formed from a single molecule are of particular interest for data storage, as the ability to store a little on each molecule could significantly increase the storage capacity of computers. Researchers have now developed a new molecular system with special magnetic hardness. The ingredients in this special recipe are rare earth metals and an unusual nitrogen-based molecular bridge, as shown in the study published in the journal Angewandte Chemie.

The ability of a molecule to become a magnetic data storage medium depends on the ability of its electrons to magnetize and resist demagnetization, also known as magnetic hardness. Physicists and chemists build molecular magnets like this from metal ions that are magnetically coupled to each other via molecular bridges.

However, these coupling bridges must meet certain criteria, such as ease of production and versatility. For example, a dinitrogen radical bridge – two nitrogen atoms with one extra electron, making dinitrogen a radical – has given exceptional results for rare earth metal ions, but is very difficult to control and does not provide ” no possibility of modification ”, explains Muralee Murugesu and her team from the University of Ottawa, Canada, in their study. To give them greater reach, the team enlarged this bridge using a “double dinitrogen”; the unexplored tetrazine ligand has four nitrogen atoms instead of two.

To produce the molecular magnet, the researchers combined the new tetrazine ligand with rare earth metals – the elements dysprosium and gadolinium – and added a strong reducing agent to the solution to form the tetrazine radical bridges. The new magnet crystallized as a dark red prism shaped glitter.

The researchers describe the molecular unit within this crystal as a tetranuclear complex in which four metal ions stabilized by a ligand are linked together by four tetrazine radicals. The most important property of this new molecule is its extraordinary magnetic hardness or coercive field. This means that the complexes formed a durable single molecule magnet which was particularly resistant to demagnetization.

The team explains that this high coercive field is obtained by a strong coupling through the tetrazine radical unit. The four metal centers of the molecule are coupled together to form a molecular unit with a giant spin. Only the predecessor of this molecule, with the dinitrogen bridge, gave a stronger coupling. However, as already mentioned, it was also much less versatile and less stable than the new tetrazine free radical bridge.

The team points out that this method could be used to produce other giant spin multinuclear complexes, offering superb opportunities to develop extremely efficient monomolecular magnets without the difficulties of previous candidates.

Reference: “Radical-Bridged Ln4 Metallocene Complexes with Strong Magnetic Coupling and a Large Coercive Field ”by Niki Mavragani, Dylan Errulat, Dr. Diogo A. Gálico, Dr. Alexandros A. Kitos, Dr. Akseli Mansikkamäki and Prof. Dr. Muralee Murugesu, August 24, 2021, Angewandte Chemie.
DOI: 10.1002 / anie.202110813

Dr Muralee Murugesu is Full Professor and University Research Chair in Nanotechnology in the Department of Chemistry and Biomolecular Sciences at the University of Ottawa in Ontario, Canada. His research focuses on the design and development of high performance monomolecular magnets, metallo-organic structures and high energy materials.