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We report on the measurements of the C-13 NMR line shape in the organic ferromagnet tetrakis(dimethylamine) ethylene-C-60 between room temperature and 4 K as well as on a simulation of the line shape in this interval. It is shown that the sudden increase in the inhomogeneous C-13 NMR linewidth in the middle of the ferromagnetic phase can be explained by the freezeout of the pseudorotations of the axes of the Jahn-Teller distortions of the C- 60(-) ions. The correlation times for the Jahn- Teller dynamics of the C-60(-) ions have been extracted from a comparison of experimental and simulated C-13 NMR line shapes. A strong correlation between spin ordering and orbital ordering has been found.

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Al-27 NMR measurements of the transverse magnetization decay in a decagonal quasicrystal Al72.6Ni10.5Co16.9 detected at temperatures between 300 and 4 K slow, low-activation-energy, diffusive atomic jumps that exhibit properties compatible with the elementary excitations of the quasiperiodic lattices in the form of phason jumps. However, identical atomic motion was observed also in "vacancy-ordered" bcc crystalline Al50Cu35Ni15, indicating that this motion is not quasicrystals specific, but a feature of close-packed atomic structures-either periodic or quasiperiodic-that contain structural vacancies.

The unusual magnetism of manganese atoms in an icosahedral Al72.4Pd20.5Mn7.1 single-grain quasicrystal was studied by Al-27 nuclear magnetic resonance (NMR), magnetic susceptibility, and electrical resistivity measurements. Between room temperature and 50 K both the Al-27 NMR linewidth and the frequency shift exhibit a Curie-Weiss-type, 1/(T-theta) temperature dependence. At lower temperatures a significant narrowing of the linewidth, concomitant with a reduction of the frequency shift is observed. These features can be explained by a gradual reduction of the local exchange magnetic field at the position of the Al-27 nuclei that is transferred from the manganese d moments via the conduction electrons. Two possible origins of this phenomenon are discussed: (i) the Kondo-like screening of manganese moments by the conduction electrons and (ii) the ''resistivity'' -damping of the RKKY interaction due to increasing electron localization at low temperatures.

Orientation-dependent 27Al quadrupole-perturbed NMR spectra of a single-grain Al72.4Pd20.5Mn7.1 icosahedral quasicrystal are reported. The dependence on orientation is a consequence of a spatially anisotropic distribution of orientations of the electric field gradient tensor at the inequivalent lattice sites. The results demonstrate that the NMR spectra of quasicrystalline single-grain samples of a macroscopic symmetry as high as icosahedral are orientation-dependent and differ from the orientation-independent spectra of powder samples, in contrast to previous reports., Ustanovili smo ovisnost kvadrupolno-smetanih spektara NMR 27Al u jednom zrnu ikosaedarskog kvazikristala Al72.4Pd20.5Mn7.1 o smjeru. Ta je ovisnost posljedica prostorno neizotropne raspodjele tenzora gradijenta električnog polja na različitim položajima u rešetci. Ishodi mjerenja pokazuju da spektri NMR kvazikristalnih jednozrnih uzoraka tako visoke simetrije kao što je ikosaedarska ovise o smjeru i razlikuju se od smjerno-neovisnih spektara praškastih uzoraka, što je suprotno ranijim izvješćima.