Hyperfine interaction measurements inLaCrO3andLaFeO3perovskites using perturbed angular correlation spectroscopy

Abstract

The perturbed angular correlation (PAC) technique was used to study the hyperfine interactions in the antiferromagnetic and paramagnetic regions of the distorted perovskites ${\mathrm{LaCrO}}_{3}$ and ${\mathrm{LaFeO}}_{3}.$ The dilute ${}^{111}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{In}}}^{111}\mathrm{Cd}$ nuclear probes were introduced into the samples through a chemical process. The present measurements cover the temperature ranges from 15 to 848 K for ${\mathrm{LaCrO}}_{3}$ and 77 to 1324 K for ${\mathrm{LaFeO}}_{3}.$ Two distinct electric-quadrupole interactions were observed in each compound. The lower quadrupole frequency was assigned to the transition-metal atom site while the higher frequency was attributed to the lanthanum site in both cases. Temperature dependence of the electric-quadrupole interaction parameters indicated structural phase transitions at around 512 and 1223 K, respectively, in ${\mathrm{LaCrO}}_{3}$ and ${\mathrm{LaFeO}}_{3}.$ The phase transitions were associated with the change from an orthorhombic to rhombohedral structure and characterized by a sudden increase in the electric field gradient ${V}_{\mathrm{zz}}$ and a decrease in the asymmetry parameter $\ensuremath{\eta}$ for both sites. PAC spectra measured below the N\'eel temperature revealed that at 0 K the supertransferred magnetic hyperfine field on ${}^{111}\mathrm{Cd}$ at the Cr site in ${\mathrm{LaCrO}}_{3}$ (2.4 T) is much smaller than at the Fe site in ${\mathrm{LaFeO}}_{3}$ (19.4 T). The magnetic field on ${}^{111}\mathrm{Cd}$ at La sites in both compounds is of the order of 0.3 T. Additional measurements were made to determine the magnetic hyperfine field using the probe nucleus ${}^{140}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{La}}}^{140}\mathrm{Ce}.$ The result reconfirmed that a relatively weak hyperfine field is supertransferred to the probe atoms at La sites.