The low-frequency dynamics of van Vleck compounds and the thermal relaxation of Pr141 in PrNi5

The analytical expression of Becker, Fulde and Keller (BFK) for the low-frequency dynamical susceptibility is generalized for an arbitrary RE ion level scheme case. The NMR linewidth of RE nucleus is calculated and it is shown that the electron-hole part of this susceptibility does not contribute to the width for T > Tsub(e). The coupling parameter j rho for PrNi5 is estimated from the available experimental data (j rho approx. 8.10-3) and it is found that the electronic susceptibility is much enhanced in PrNi5, (1 - α)-1 approx. equal to 10. It is argued that the single ion-conduction electron process cannot explain the thermal relaxation of Pr141 in PrNi5 and the importance of incorporating the RKKY exchange mechanism in the frame of the first principle theory of BFK is discussed. (orig.)