High-temperature phase transitions and low-temperature magnetic ordering in SrRuO3 and CaRuO3 ceramics studied using perturbed-angular-correlation spectroscopy.

Abstract

Perturbed-angular-correlation (PAC) spectroscopy was used to measure nuclear-electric-quadrupole interactions in the orthorhombically-distorted perovskites ${\mathrm{SrRuO}}_{3}$ and ${\mathrm{CaRuO}}_{3}$ over temperatures ranging from laboratory to very high temperatures. At 77 K, PAC spectroscopy was used to measure combined electric-quadrupole and magnetic-dipole interactions in magnetically ordered ${\mathrm{SrRuO}}_{3}$ and pure electric-quadrupole interactions in paramagnetic ${\mathrm{CaRuO}}_{3}$. The $^{111}\ensuremath{\rightarrow}^{111}$Cd PAC probe was used for these measurements, and it substituted into the Ru site in ${\mathrm{SrRuO}}_{3}$ and very likely into the Ru site in ${\mathrm{CaRuO}}_{3}$. The temperature dependence of the electric-field-gradient (EFG) parameters for ${\mathrm{SrRuO}}_{3}$ indicates the onset of a structural phase transition at approximately 800 K. The presence of this transition indicates that the laboratory-temperature structure of ${\mathrm{SrRuO}}_{3}$ has lower-than-cubic symmetry. At very high temperatures >1600 K, the structure of ${\mathrm{CaRuO}}_{3}$, as given by the EFG parameters, becomes very similar to the laboratory-temperature structure of ${\mathrm{SrRuO}}_{3}$. At 77 K in ${\mathrm{SrRuO}}_{3}$, the measured Ru-site supertransferred hyperfine field is 39\ifmmode\pm\else\textpm\fi{}3 kOe. Using $^{99}\mathrm{Ru}$ and $^{57}\mathrm{Fe}$ M\"ossbauer-effect information and other $^{111}\ensuremath{\rightarrow}^{111}$Cd PAC measurements, the magnetic hyperfine fields at the Ru site in ${\mathrm{SrRuO}}_{3}$ and at the Fe site in ${\mathrm{PrFeO}}_{3}$ are compared.