NUCLEAR-MAGNETIC-RESONANCE MEASUREMENTS IN RARE-EARTH GROUP-V A INTERMETALLIC COMPOUNDS

The temperature dependences, signs, and magnitudes of the phosphorus, arsenic, antimony, and bismuth nuclear-magnetic-resonance (NMR) Knight shifts in the NaCl-type rare-earth group-VA intermetallic compounds have been studied in detail for the temperature range of 1.5-600°K. The Knight shifts in the nonmagnetic compounds, such as LaP, were found to be temperature-independent. For most of the magnetic compounds, such as GdP, the temperature-dependent part of the Knight shift was found to obey a Curie-Weiss law. However, for the praseodymium, samarium, and thulium compounds, the effect of the sixfold cubic crystal-field interaction on the rare-earth ion could not be neglected. An analysis, showing the relationship between the Knight shift and the rare-earth 4f paramagnetic susceptibility χf(T), is presented. In this manner, it is shown that detailed information about χf(T) can be derived from an analysis of the NMR data. Furthermore, it is shown that the hyperfine field at the nonmagnetic site in these compounds arises from the spin component S of the total angular momentum J of the rare-earth ion, and not from the magnetization at the rare-earth site. The s-f exchange energies Γ for these compounds were calculated using the uniform conduction-electron spin-polarization model for the Knight shift. For the rare-earth Group-VA intermetallic compounds, Γ was found to be negative (antiferromagnetic) and relatively constant (-0.3 eV) for all of these compounds. Comparisons are made for the s-f exchange energies for all of the various rare-earth intermetallic compounds for which NMR measurements are available. It is again found that Γ is negative and relatively constant in magnitude. For all of these compounds, the total hyperfine field per unit spin S is found to be of the order of -50 kOe. No explanation for this phenomenon is advanced. It is shown that a consistent analysis of the Knight-shift data in terms of the Ruderman-Kittel-Kasuya-Yosida theory is probably impossible. The NMR linewidths δH in the nonmagnetic compounds were found to be in agreement with the calculated dipolar contribution, while for the magnetic compounds, the NMR linewidth δH was found to be due to the presence of demagnetization fields arising from the nonspherical shape of the particles in the powdered samples. © 1969 The American Physical Society.