Origin of ${\mathit{T}}_{\mathit{c}}$ suppression and magnetic ordering in ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$

The magnetic 4f excitation spectrum of ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ was measured by use of inelastic neutron scattering in a study of the ground-state properties of praseodymium. We analyzed the spectra in terms of crystal-field transition lines of a trivalent Pr ion. The absolute widths of the magnetic transition lines were found to be enhanced compared with those in stable R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ compounds, where R is a rare-earth element. A distinct ‖Q‖ dependence of the inelastic magnetic intensities was found due to spatial magnetic correlations even above the unexpectedly high ordering temperature of the Pr magnetic moments. Both the enhanced width and the magnetic correlations are almost independent of the oxygen concentration. The enhanced widths indicate an increased hybridization between 4f electrons and electrons of the ${\mathrm{CuO}}_2$ planes. This is certainly responsible for the ${\mathit{T}}_{\mathit{c}}$ suppression in ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, probably indirectly through the unexpectedly strong magnetic correlations (high ordering temperature) of the Pr magnetic moments caused by this enhanced hybridization.