Molecule-based magnets

Molecule-based magnets (MBMs) or molecular magnets are a class of materials capable of displaying ferromagnetism and other more complex magnetic phenomena. This class expands the materials properties typically associated with magnets to include low density, transparency, electrical insulation, and low-temperature fabrication, as well as combine magnetic ordering with other properties such as photoresponsiveness. Essentially all of the common magnetic phenomena associated with conventional transition-metal magnets and rare-earth magnets can be found in molecule-based magnets. Prior to 2011, MBMs were seen to exhibit "magnetic ordering with Curie temperature (Tc) exceeding room temperature". The first synthesis and characterization of MBMs was accomplished by Wickman and co-workers in 1967. This was a diethyldithiocarbamate-Fe(III) chloride compound. In February 1992, Gatteschi and Sessoli published on MBMs with particular attention to the fabrication of systems in which stable organic radicals are coupled to metal ions. At that date, the highest Tc on record was measured by SQUID magnetometer as 30K. The field exploded in 1996 with the publication of a book on "Molecular Magnetism: From Molecular Assemblies to the Devices". In February 2007, de Jong et al. grew thin-film TCNE MBM in situ, while in September 2007, photoinduced magnetism was demonstrated in a TCNE organic-based magnetic semiconductor. The June 2011 issue of Chemical Society Reviews was devoted to MBMs. In the editorial, written by Miller and Gatteschi, are mentioned TCNE and above-room-temperature magnetic ordering along with many other unusual properties of MBMs. The mechanism by which molecule-based magnets stabilize and display a net magnetic moment is different than that present in traditional metal- and ceramic-based magnets. For metallic magnets, the unpaired electrons align through quantum mechanical effects (termed exchange) by virtue of the way in which the electrons fill the orbitals of the conductive band.

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