The first experimental evidence of room-temperature magnetocaloric effect in fullerenes

The aim of the study was the first characterization of fullerenes, organic molecular solids without a d or f metal/ion, as paramagnets with the magnetocaloric effect (MCE) displayed at the temperatures close to room. Direct determinations of MCE/magnetization thermodynamic parameters and a heat capacity of [60]fullerene (C-60) and 1 '-N-methyl-2 '-(pyridin-4-yl)pyrrolidino[3 ',4 ':1,2][60]fullerene (PyC60) in aqueous suspensions were performed by means of original microcalorimetric method and differential scanning calorimetry, respectively. Both materials display positive MCE that has been determined to be 0.004 and 0.016 K at 278 K in C-60 and PyC60, respectively, when the magnetic induction changes from zero to 1.0 T. The increase in PyC60 MCE is observed despite the fact that the molar heat capacities values of substituted fullerene are two times higher than that of C-60. These results along with calculated full energies, bond lengths and a charge on atoms according to Mulliken in fullerenes (PM3 and the Hartree-Fock in the basis of 3-21G, using Gaussian03) are interpreted as a reflection of an aromaticity and antiaromaticity areas state in fullerenes.