Impurity-Induced Nuclear Spin-Lattice Relaxation in Metals: A New Approach

We find an $\exp [-{\left(\frac{t}{{\tau }_1}\right)}^{\frac{1}{2}}]$ time dependence for the recovery of the ${\mathrm{Al}}^{27}$ nuclear magnetization in the system ${\mathrm{La}}_{1-c}{\mathrm{Gd}}_c{\mathrm{Al}}_2$. This is characteristic of diffusionless relaxation and an especially direct interpretation of the data is possible in this limit. Variation of ${\tau }_1$ with temperature and magnetic field indicates that longitudinal dipolar fluctuations of the Gd moments relax the ${\mathrm{Al}}^{27}$ nuclei while its concentration dependence indicates Ruderman-Kittel-Kasuya-Yosida coupling between the Gd spins.