Electron spin-lattice relaxation in noncommon metals YBa2Cu3Ox and Rb1C60

Using an original modulation technique, the electron spin-lattice relaxation have been investigated in two noncommon metals: YBa2Cu3Ox, high-T-c material doped with 1% Gd, and Rb1C60, linear polymer phase fulleride. In the first case, the Korringa-like temperature dependence of the Gd3+ longitudinal relaxation time T-1 is found for x = 6.59 in a wide temperature range 4.2 < T < 200 K, both above and below T-c = 56 K. At x = 6.95 (T-c = 90 K), the T-1 behavior within 50 < T < 200 K is evidently affected by spin gap opening with the gap value of about 240 K. At 200 K, an unexpected acceleration of the relaxation rate takes place, suggesting some change in the relaxation mechanism. The data are discussed in terms of the Barnes-Plefke theory with allowance made for microscopic separation of the normal and superconducting phases. In Rb1C60, the evolution of the ESR line and relaxation rates have been studied accurately in the range of the metal-insulator transition (below 50 K). Interpretation is suggested which takes into account breaking down the relaxation bottleneck due to opening of the energy gap near the Fermi surface. The gap value of about 100 cm(-1) is estimated from the analysis of relaxation rates, lineshape and spin susceptibilities.