Magnetic-field-induced slowing-down of molecular rotation in C60 crystals

The molecular dynamics of C-60 crystals was studied by inelastic neutron scattering at T=290 K, i.e., above the first-order phase transition temperature (T-C approximate to 260 K), in the region of free C-60-spheroid rotation in the lattice. The energy broadening of the original neutron spectrum 2Gamma(0)approximate to0.1 meV for a momentum transfer q=2 Angstrom(-1) is in agreement with NMR data on the rotational relaxation time of the molecule tausimilar to10(-11) ssimilar to(h) over bar/Gamma(0). This effect was observed to decrease in magnetic fields H=2.5-4.5 kOe applied along the scattering vector: Gamma(H)=0.7Gamma(0). The slowing-down of the molecular rotation is discussed in connection with the interaction of a magnetic field with the molecular currents, which fluctuate when the C-60 cage rotates. (C) 2002 MAIK "Nauka/Interperiodica".