Spin-Echo Measurements of Spin-Spin Interactions in Metals: Tin and Cadmium

Modulated structure of the nuclear spin-echo envelope has been studied in metallic solid solutions. The modulation is due to microscopic broadening of the NMR line. The modulation period $2{\tau }_M$ has been calculated as a function of the two coupling constants $J$ (exchange) and $B$ (total dipolar), taking into account the signs of these interactions. In order to examine the effect of departures from the hypotheses of the theory, the dc field variation of the spin-echo envelopes has been studied in a Pt-Au alloy with rf fields smaller than the linewidth. Modulated echo envelopes have been observed in cadmium- and tin-based alloys. In the Cd-Mn system, two modulations of the ${\mathrm{Cd}}^{111}$ signals were present, whose corresponding periods $2{\tau }_M$ were 3.1±0.15 and 4.2±0.2 msec. In tin alloys, one frequency only could be resolved for ${\mathrm{Sn}}^{119}$ corresponding to $2{\tau }_M=0.54\mathrm{}\pm 0.04$ msec. The measured second moments of the lines of pure Cd and pure Sn, together with the preceeding data, have been used to obtain the value of the exchange coupling $J$ for first nearest neighbors ($J=4.1\mathrm{}$ kHz for Sn, $J=0.5\mathrm{}$ kHz for Cd), while an order of magnitude has been deduced for the pseudodipolar interaction. A similar analysis has also been applied to previous measurements on lead. The results are discussed and compared with estimates based on the Ruderman-Kittel approximation.