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

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Abstract
The molecular dynamics of C60 crystals was studied by inelastic neutron scattering at T=290 K, i.e., above the first-order phase transition temperature (TC≈260 K), in the region of free C60-spheroid rotation in the lattice. The energy broadening of the original neutron spectrum 2Γ0≈0.1 meV for a momentum transfer q=2 Å−1 is in agreement with NMR data on the rotational relaxation time of the molecule τ∼10−11 s∼ ℏΓ0. This effect was observed to decrease in magnetic fields H=2.5–4.5 kOe applied along the scattering vector: ΓH=0.7Γ0. 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 C60 cage rotates.