We report the first indication for a nuclear spin-lattice relaxation mechanism originating from the coupling of the impurity nuclei to nuclear magnons. The magnetic hyperfine interaction and the nuclear spin-lattice relaxation of ${}_{}{}^{191}{}_{}{}^{}P\mathrm{t}$ $(T_{1/2}=2.8\mathrm{}\mathrm{d})$ in fcc Co were measured with NMR on oriented nuclei at temperatures between 8 and 14 mK in external magnetic fields $B_{\mathrm{ext}}=0.1\mathrm{}–10\mathrm{kG}$. Between $B_{\mathrm{ext}}=5\mathrm{}$ and $1\mathrm{kG}$ the relaxation rate increases by 2 orders of magnitude. This increase is attributed to the interaction of ${}^{191}\mathrm{Pt}$ with nuclear magnons originating from the ${}^{59}\mathrm{Co}$ nuclear spin system.

• Received 27 February 1997

DOI:https://doi.org/10.1103/PhysRevLett.78.5002