engleski

Transition to inhomogeneous ferromagnetic state in TDAE-C60at low temperatures

C-13 NMR spectra of a 40% C-13-enriched well- annealed TDAE-C-60 powder sample show a huge increase in the C-13 NMR linewidth, accompanied by an increase in C-13 spin-lattice relaxation time T-1, on cooling below T' = 10 K. On the other hand, the TDAE methyl proton NMR spectra of a well-annealed TDAE-C-60 single crystal at 6.34 T show, in the ferromagnetic phase between T-c = 16 K and T' = 10 K, the presence of two broad inhomogeneous lines with their centers shifted by 2.5 MHz and 0.5 MHz, respectively, from the proton Larmor frequency. The intensity of the strongly shifted proton NMR line, which dominates the H-1 spectra between T-c and T' in the ferromagnetic phase, continuously decreases with decreasing temperature and becomes suddenly very small below T. This indicates a dramatic decrease of the unpaired spin density at one half of the TDAE proton sites and could result from the near disappearance of one of the two alternating ferromagnetic C-60(-) orientations below T' as suggested by the structural model of Narymbetov et al. involving increased C-60(-) orientational disorder at low temperatures.

SINGLE-CRYSTAL ; TDAE

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