Nuclear Magnetic Resonance in Exchange-Enhanced Metals:Rh103Knight Shifts and Relaxation Rates in Palladium-Rhodium and Nickel-Rhodium Alloys

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Abstract
Low-temperature (T≈1−4°K) measurements of the resonance shift K, spin-lattice relaxation time T1, and inhomogeneous linewidth W of Rh103 in the two alloy systems Pd1−xRhx (0.02≤x≤1) and Ni1−xRhx (0.38≤x≤1) have been carried out using transient NMR techniques. In Pd1−xRhx both T1T and K vary monotonically with K decreasing from +0.43 to -15%, and T1T from 9.2 to 0.7 sec °K. Similar results are found in Ni1−xRhx, with K decreasing from +0.43 to -8.1%, and T1T from 9.2 to 1.2 sec °K. The Rh103 NMR in both alloy systems is characterized by severe inhomogeneous broadening, with W approaching K in magnitude in some cases. This result demonstrates that the local susceptibility is very sensitive to statistical variations in the near-neighbor alloy composition. The minimum K value in Pd-Rh agrees with the infinite-dilution value K=−14.7% obtained by Rao, Matthias, and Shirley using perturbed-angular-correlation techniques, and indicates that K is essentially independent of x for Rh concentrations up to ∼ 5 at.%. A comparison of this result with the Pd105 Knight shift in palladium metal shows that the local susceptibility at the rhodium sites is approximately three times greater than the palladium host susceptibility. This deviation from rigid-band behavior develops gradully with decreasing rhodium concentration for x<0.4. In contrast, the Ni-Rh NMR data suggest that the rhodium susceptibility is significantly smaller than the nickel susceptibility at all rhodium concentrations. An analysis of the Rh103 shift and relaxation data for Pd-Rh and Ni-Rh demonstrates that both quantities are dominated by an exchange-enhanced d-spin (core-polarization) hyperfine mechanism for sufficiently low rhodium concentrations. Moreover, the observed relationship between

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