Nuclear quadrupole interaction studies ofC15RMn2hydrides (R=Y,Gd,Tb,Dy)

Abstract

The nuclear electric quadrupole interaction (QI) of the probe nucleus $^{111}\text{I}\text{n}/^{111}\text{C}\text{d}$ in the paramagnetic phase of the $C15$ rare earth $(R)$--manganese hydrides (deuterides) $R{\text{Mn}}_{2}\text{H}{(D)}_{x}$, with $R=\text{Y}$, Gd, Tb, and Dy, has been investigated by perturbed angular-correlation spectroscopy. The QI between the $^{111}\text{C}\text{d}$ quadrupole moment and the electric-field gradient (EFG) at the probe nucleus on the Mn site has been measured as a function of temperature in ${\text{TbMn}}_{2}\text{H}{(D)}_{x}$ in the concentration range $0\ensuremath{\le}x\ensuremath{\le}4.3$ and in $R{\text{Mn}}_{2}\text{H}{(D)}_{x}$, $R=\text{Y}$,Gd,Dy at the highest H content of $x\ensuremath{\sim}4.3$. The relative temperature dependence of the EFG in the parent compounds $R{\text{Mn}}_{2}$ is twice as strong as in isostructural $R{\text{Al}}_{2}$ which can be related to differences in the Debye temperatures resulting from different radius ratios ${r}_{R}/{r}_{\text{Mn}}$ and ${r}_{R}/{r}_{\text{Al}}$ [Joseph-Gschneidner postulate, Scr. Metall.2, 631 (1968)]. Hydrogenation of $R{\text{Mn}}_{2}$ increases the magnitude of the EFG by a factor of 2 between $x=0$ and $x=4.3$ but leaves the relative temperature dependence almost unchanged. Only at concentrations $x>3.6$ the temperature coefficient of the QI is significantly larger than in uncharged $R{\text{Mn}}_{2}$. These results are compared with the much stronger concentration dependence and the anomalous temperature dependence of the QI of $^{111}\text{C}\text{d}$ in the $C15$ hydrides ${\text{HfV}}_{2}{\text{H}}_{x}$. Evidence for an exceptionally high H mobility in ${\text{TbMn}}_{2}{\text{H}}_{x}$ is presented. The measurements provide information on structural changes and magnetic ordering temperatures at different H concentrations.