State of the Art

References

Ferrocarbon Consortium
Parco Area delle Scienze, 7a
43100 Parma, ITALY
Tel.: +39-0521-905-217
Fax: +39-0521-905-223
Email: ferrocarbon@fis.unipr.it


Background and State of the Art

  1. Carbon is an extraordinary element, not only does the versatility of its bonding make life possible, the number of known allotropes of pure carbon continue to grow, producing materials like fullerenes and nanotubes and their derivatives which are both scientifically fascinating and have huge numbers of potential applications. Despite many decades of work, even the properties of the parent compound graphite are still poorly understood. Although it is familiar to most people for its long list of everyday applications such as in pencils or as a lubricant or even as a weapon against electrical installations; unexpected behaviour has been reported recently, including two-dimensional electronic transport [1, 2], metal-insulator transitions [3, 4], extraordinary magneto-resistance [2, 5], magneto-striction and even superconductivity [6];
  2. Although Heisenberg rejected the idea of p-electron magnetism [7], prior to the turn of the millennium nearly 100 papers and 30 patents describing ferromagnetic structures containing either pure carbon or carbon combined with first row elements [8] were published. These reports were difficult to reproduce, but in more recent years the discovery of room temperature ferromagnetism has galvanized interest in this field and reports have been published that describe more precisely how to make carbon magnetic. These recent findings have attracted huge interest in the scientific community; the discovery of ferromagnetism in pressure-polymerized fullerenes was included in Top-Ten of Physics in 2001 and in Chemistry Highlights-2001 [9, 10], and the fact that graphite can also be turned ferromagnetic through irradiation lead the newsletter of the American Physical Society to choose this topic for its Focus page [11], concentrating on the possibility of producing "mini magnets" with possible applications in nanoscale electronics;
  3. At high temperatures and pressures C60 polymerises through a cyclic-addition process to form a series of one, two or three-dimensional phases [12, 13] with electronic properties ranging from semi-conducting to metallic and a wide range of mechanical properties, including persistent reports of a three-dimensionally polymerised phase with remarkable hardness [14, 15], and ferromagnetism in the 2D polymerized phase [16]. The weakness of the magnetism so far observed is due to the dilution of (compact) magnetic areas. But what differentiates this from other fullerene or organic magnets is the Curie temperature, which is well above 300 K, attracting the interest of the whole magnetism community. "Nature" commented the discovery of room-temperature ferromagnetism in fullerenes as follows: "If confirmed, it will be a breakthrough in material science" [17];
  4. Bombarding graphite or fullerene thin films with high energy protons produces similar ferromagnetic behaviour [18], opening the intriguing possibility of producing ferromagnets patterned on scales of around 1 µm or below [19]. This has huge technological implications, with potential device applications in spintronics, optics and quantum computing;
  5. Although room temperature magnetism in carbon was predicted theoretically many years ago, its experimental observation was still a surprise to many, and it still remains controversial. There has been an avalanche of theoretical models attempting to explain these observations [20]. In the fullerenes these include: the possibility of self-doping from small amounts of cage collapse and the fracture of the interfullerene bonds causing unpaired spins;
  6. Polymerisation of fullerenes can be realized through high-pressure and temperature treatments and through irradiation with UV light. But it can also occur through reactions with alkali metals [21]. The intercalation of small radius alkali metals like lithium give a large variety of C60 polymeric structures with possible new magnetic, conductive and superconductive properties [22, 23]. So the ability of electron donor atoms to promote polymerisation combined with the control of the cyclo-addition process should open up the possibility of producing new and interesting materials.