Cd111time-differential perturbed angular correlation study of pressure-induced valence changes inYbAl2

Abstract

The quadrupole interaction at $^{111}\mathrm{Cd}$ impurity nuclei in the intermediate-valence compound $\mathrm{Yb}{\mathrm{Al}}_{2}$ has been measured under pressure up to $80\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$ by the time-differential perturbed angular correlation spectroscopy. It was found that the quadrupole frequency ${\ensuremath{\nu}}_{Q}$ measured on the $^{111}\mathrm{Cd}$ nuclei located at the Al sites in $\mathrm{Yb}{\mathrm{Al}}_{2}$ varies nonlinearly and increases by almost four times with the pressure increase up to $80\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. A linear correlation between the mean Yb valence, derived from Yb ${L}_{3}$ OFY-XAS and RXES measurements, and the electric field gradient (the quadrupole frequency ${\ensuremath{\nu}}_{Q}=eQ{V}_{zz}∕h$) has been observed. The quadrupole frequencies on $^{111}\mathrm{Cd}$ in the $\mathrm{Gd}{\mathrm{Al}}_{2}$, $\mathrm{Yb}{\mathrm{Al}}_{3}$, $\mathrm{Tm}{\mathrm{Al}}_{3}$, and $\mathrm{Ca}{\mathrm{Al}}_{2}$ compounds have been also measured. The possibility of determining the valence of Yb in the Yb compounds with $p$ metals from the relation ${\ensuremath{\nu}}_{Q}\mathbf{(}\ensuremath{\upsilon}(P)\mathbf{)}={\ensuremath{\nu}}_{2}+({\ensuremath{\nu}}_{3}\ensuremath{-}{\ensuremath{\nu}}_{2})\ensuremath{\upsilon}(P)$ has been considered.