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Surface-grafted metallofullerene molecular magnets with controllable alignment of magnetic moments

Periodic Reporting for period 3 - GraM3 (Surface-grafted metallofullerene molecular magnets with controllable alignment of magnetic moments)

Reporting period: 2018-06-01 to 2019-11-30

Realization of magnetism on a molecular level is very technologically attractive since it promises a dramatic increase of possible writing densities and offers a number of spintronics applications, including memory storage and quantum computing. Successful development in this direction will result in miniaturization of the devices with concomitant decrease of their energy consumption. These applications require that the magnetic molecules (single molecule magnets, SMM, hereafter) are to be organized on the substrates and their magnetic states are controlled on the single-spin level. The practical realization of such technologies are however hampered by the low temperatures of magnetic phenomena, difficulties in the obtaining of the well-structurally defined layers of SMMs, and fundamental difficulties in “writing” and “reading” information from single molecules. The main goal of this project is to overcome these problems by utilizing unique properties of endohedral metallofullerenes (EMFs) with lanthanide ions as magnetic centers. EMFs are chemically and thermally stable, which allows their further functionalization and implementation in molecular devices. This project is hence focused on the advances in synthesis of the EMFs and development of new EMF molecules with improved magnetic properties, functionalization of the EMF molecules with chemical groups facilitating formation of the single-molecule thick layers on conducting substrates, and on the studies of the magnetic properties of EMFs and their derivatives in bulk and on substrates.
At the first stage of the project, we focused on the improvement in the synthesis of EMF molecules, which would allow their faster accumulation and further studies of their chemical and magnetic properties. A number of magnetic EMFs with endohedral Dy atoms have been synthesized in appreciable amounts, and selectivity of the EMF synthesis has been improved via development of the reactive gas approach. Furthermore, we have discovered a synthetic route to stabilize single-electron lanthanide-lanthanide bonds inside fullerene cages. Due to the strong exchange coupling of the magnetic moments of lanthanide ions mediated by the unpaired electron spin, such dimetallofullerenes exhibit unprecedented magnetic properties. To functionalize magnetic fullerenes with surface-anchoring groups, several derivatization reactions were studied, and the most convenient functionalizatin approach was identified. The first chemical derivatives of magnetic fullerene molecules with anchoring groups have been thus synthesized via 1,3-dipoalr cycloaddition followed by the formation of self-assembled monolayers on gold. This progress opened the possibility for the studies of their bulk and surfaces magnetism, which showed that (a) chemical functionalziation significantly changes magnetic properties of endohedral fullerenes and that self-assembled monolayers of magnetic fullerenes exhibit magnetic bistability on gold. In parallel, the work on the monolayer formation by organic molecular beam epitaxy with subsequent studies of the layers by scanning tunneling microscopy and X-ray magnetic circular dichroism has been pursued. Well-ordered monolayers of Dy2ScN@C80 have been obtained, and XMCF progved that they retain magnetic properties on Au and Ag. Ab initio and DFT computational studies of chemical derivatives, on-surface arrangement, and magnetic properties of pristine and chemically modified EMFs have been performed successfully.
During the first period of the project, the molecules with unprecedentedly high blocking temperatures of magnetization and unusual mechanisms of relaxation of magnetization have been found. In particular, we have discovered that dimetallofullerenes featuring single-electron metal-metal bonds have very promising magnetic properties due to the exchange strong coupling of the lanthanide magnetic moments. The studies of the surface magnetism showed that monalyers of magnetic fullerenes retain good magnetic properties on metal substrates. These results open the new way for creation of single molecule magnets with unusual magnetic and electronic properties.