Crystal field properties of f-electron states in RBa₂Cu₃O₇ for R=Ho, Nd and Pr

The authors present details of their predictions for the crystal-field split levels in RBa₂Cu₃O₇ compounds with R=Nd³⁺ (f^{3 4}I_9/2) and Pr³⁺ (f²³H₄) based on the previously reported crystal-field split energy levels of f¹⁰⁵I₈ for Ho³⁺ in HoBa₂Cu₃O₇. Their predictions of the overall distributions of crystal-field levels provide the framework for interpretation of inelastic neutron scattering spectra of NdBa₂Cu₃O₇ and PrBa₂Cu₃O₇. For NdBa₂Cu₃O₇ the inelastic scattering peaks are clearly seen and can be well assigned in terms of the energy levels of f³⁴I_9/2 by a small re-scaling of the predicted crystal-field parameters to adjust the overall width of the calculated spectrum. In the case of PrBa₂Cu₃O₇ several important inelastic scattering features, particularly the lowest energy ones, are so unusually broad and weak that it was difficult to identify them without predictions of this type. Enough features in the scattering spectra have now been assigned for us to obtain fitted values for the crystal-field parameters of Pr³⁺ and Nd³⁺ in RBa₂Cu₃O₇. As tests of these new assignments they discuss predictions of the anisotropies of magnetic susceptibility, and the thermodynamic functions for the paramagnetic phase of PrBa₂Cu₃O₇. Finally, a primitive model for interactions between Pr³⁺ ions is used to give an initial interpretation of the saturation moment that has been reported for the antiferromagnetically ordered phase of PrBa₂Cu₃O₇. They conclude that standard crystal-field theory correctly applied to the f² configuration of the Pr³⁺ ions fully explains the unusual magnetic properties of PrBa₂Cu₃O₇.