Magnetization of a large single ${\mathrm{C}}_{60}$ crystal was measured as functions of applied field and temperature. At $T=260\mathrm{}$ K, a discontinuity in susceptibility was observed. The relative change in total moment is 1.2%, independent of applied field to within experimental accuracy. This discontinuity is attributed to the change in the intramolecular geometry at the orientational order-disorder transition. This is the first experimental demonstration that the cooperative phase transition affects the magnetic susceptibility of a single molecule.

• Received 21 March 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.186