PROTON NMR IN A TDAE-C-60 SINGLE-CRYSTAL

The temperature dependence of the methyl proton NMR shift of a TDAE-C- 60 single crystal follows a Curie-Weiss law above T-C with a positive Curie temperature T-C approximate to 12 K as expected for the case of a ferromagnetic transition. Below T-C the shifts are proportional to t he magnetization and saturate below 10 K. The internal field at the TD AE protons amounts at 6 K to 600 G and exceeds by an order of magnitud e the internal field determined by electron-spin resonance at the C-60 (-) ions. The result shows that in addition to the direct C-60(-)-C-60 (-) interactions which seem to be of antiferromagnetic nature, a part of the exchange coupling between the C-60(-) ions is mediated by the T DAE(+) groups. It is this indirect coupling which might give rise to t he Dzyaloshinsky-Moriya term in the spin Hamiltonian which is responsi ble for weak ferromagnetism in this system.