Magnetic Properties of Dilute Gold-Vanadium Alloys: Nuclear Magnetic Resonance inAuVandAu(Ag)V

Abstract

The low-temperature (1-4°K) magnetic properties of dilute (0.1-10 at.%) $\mathrm{Au}\mathrm{V}$ alloys have been studied by means of pulsed-NMR techniques. The previously reported ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ line-shape anomaly for vanadium concentrations near 1 at.% is shown to result from a large reduction in the vanadium spin susceptibility for vanadium impurities that are nearest neighbors to each other. The observed change in the ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ resonance shift from a negative value (-1.5%) at low vanadium concentrations to a positive value (+0.6%) at high concentrations is consistent with the expected variation in the ratio of "nonmagnetic" to "magnetic" vanadium concentrations. The nuclear resonances are severely broadened as a result of oscillatory spindensity disturbances associated with $d$-resonance scattering of the host conduction electrons. There is no indication, however, that the field-induced impurity magnetization gives rise to significant long-range negative-definite spin polarizations in the host metal as suggested recently. This conclusion is supported by the absence of positive ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}$ resonance shifts in ternary $Au\left(\mathrm{Ag}\right)\mathrm{V}$ alloys containing up to 20 at.% silver. In general, our measurements suggest that "magnetic" as well as "nonmagnetic" vanadium sites can be described by a virtual bound $d$-state model in which the impurity susceptibility, resonance shift, and nuclear-spin relaxation rates are enhanced by local Coulomb interactions. The two types of vanadium sites are distinguished by different enhancement factors, or, equivalently, different spin-fluctuation frequencies. The ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ spin-lattice relaxation rates ${T_1}^{-1\mathrm{}}$ are directly proportional to the absolute temperature over the entire composition range. In the infinite-dilution limit $T_{1}T\approx 17$ msec°K, while at high concentrations $T_{1}T$ approaches the metallic vanadium value. An analysis of the infinite-dilution ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ shift and relaxation-rate data indicates that the impurity-site spin susceptibility accounts for most of the measured bulk susceptibility.