Nuclear magnetic relaxation in niobium metal

Measurements of spin-lattice and transverse relaxation rates of 93 Nb nuclei in various samples of niobium have been measured by a pulsed radio-frequency method in a temperature range of 20-30 °K. The rates were sample dependent. Transverse relaxation in the best sample corresponded to a near-Lorentzian line of width 7 5 oersted. The dipolar line width was estimated to be 7.2 oersted. The best value for the product of spin-lattice relaxation time and temperature was found to be temperature independent and equal to 0.358 ± 0.01 sec degk. This value differs from the value of 0.190 sec degk measured by Asayama and Itoh in 1962 and the value of 0.132-0.147 sec degk predicted theoretically by Yafet and Jaccarino in 1964. The discrepancy between the new measured value and theory is discussed in the light of recent theoretical and experimental developments. It is not reduced by plausible modifications of the band structure. Enhancement of the electron specific heat by a factor of roughly 2-3 due to many-body effects could account for the discrepancy.