Investigation of spin transition in GdCoO 3 by measuring the electric field gradient at Co sites

Abstract

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 GdCoO 3 perovskite using 111Cd and 181Ta nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced in the oxide lattice through chemical process during sample preparation and were found to occupy only the Co sites in GdCoO 3. The efg's at 111Cd and 181Ta show temperature dependence with two different fractions each that change with temperature. In the case of 111Cd the quadrupole frequency slowly decreases, with corresponding increase of the temperature and shows a peak like structure at around 200 K 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 Co 3 + ion similar to LaCoO 3 compound. Indication of a Jahn–Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.