24 K MAGNETISM IN NONSTOICHIOMETRIC TDAE-C-60

The organic magnetic material TDAE-C-60 is investigated by magnetic su sceptibility, ESR and Raman measurements. We find that, depending on p reparation technique, the critical temperature (as determined by ESR) can vary from 16 to 24 K, the latter being the highest T-c reported so far for this compound or any non-polymeric organic material composed entirely of first-row elements. The ESR linewidths in the magnetic sta te - an indication of the magnitude of the internal field - vary betwe en 15 and 50 Gauss. Rather unexpectedly, Raman spectra of the 16 K mat erial do not show a clear 6 cm(-1) shift of the C-60 pentagonal pinch mode frequency relative to pure C-60 corresponding to transfer of one electron in the ground state. Instead we obtain a sharp line at 1466 c m(1) which would imply only a partial charge transfer from TDAE to C-6 0 i.e. a resonating molecular charge sharing between C-60 and TDAE mol ecules. In contrast, the 24 K sample shows a broad set of lines shifte d to lower frequency implying that the higher T-c materials may be non -stoichiometric.