Investigation of spin transition in GdCoO3 by measuring the electric field gradient at Co sites

In the present work, the time differential perturbed angular correlation (PAC) technique was used to study the temperature dependence of electric field gradient (efg) in GdCoO3 perovskite using Cd-111 and Ta-181 nuclear probes. The radioactive parent nuclei In-111 and Hf-181 were introduced in the oxide lattice through chemical process during sample preparation and were found to occupy only the Co sites in GdCoO3. The efg's at Cd-111 and Ta-181 show temperature dependence with two different fractions each that change with temperature. In the case of Cd-111 the quadrupole frequency slowly decreases, with corresponding increase of the temperature and shows a peak like structure at around 200K and a discontinuity at 700 K. These changes have been interpreted as thermally activated spin-state transitions from low-spin ground state configuration to the intermediate-spin state and from intermediate-spin to high-spin state of Co3+ ion similar to LaCoO3 compound. Indication of a Jahn-Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out. (C) 2008 Elsevier B.V. All rights reserved.