Hyperfine interaction measurements in LaCrO3 and LaFeO3 perovskites using perturbed angular correlation spectroscopy -: art. no. 224104

The perturbed angular correlation (PAC) technique was used to study the hyperfine interactions in the antiferromagnetic and paramagnetic regions of the distorted perovskites LaCrO3 and LaFeO3. The dilute In-111 --> Cd-111 nuclear probes were introduced into the samples through a chemical process. The present measurements cover the temperature ranges from 15 to 848 K for LaCrO3 and 77 to 1324 K for LaFeO3. 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 LaCrO3 and LaFeO3. 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 VE; and a decrease in the asymmetry parameter eta for both sites. PAC spectra measured below the Neel temperature revealed that at 0 K the supertransferred magnetic hyperfine field on Cd-111 at the Cr site in LaCrO3 (2.4 T) is much smaller than at the Fe site in LaFeO3 (19.4 T). The magnetic field on Cd-111 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 La-140 --> Ce-140. The result reconfirmed that a relatively weak hyperfine field is supertransferred to the probe atoms at La sites.