Spin transitions of Co ions in RCoO_(3) (R(velence)Gd,Tb) investigated by measuring the electric field gradient at R and Co sites

摘要

Hyperfine interactions in perovskite-structure RCoO_(3) (R(velence)Gd,Tb) compounds have been measured by perturbed angular correlation technique using ~(111)Cd and ~(181)Ta nuclear probes. The electric quadrupole interactions at ~(111)Cd show two different sites, assigned to probe substituting Gd or Tb and Co atoms. The temperature dependence of quadrupole frequencies shows discontinuities which have been interpreted as thermally activated spin-state transitions from low-spin ground state configuration to the intermediate-spin (IS) state and from IS state to high-spin state of Co~(3+) ion. For ~(181)Ta only one major interaction was observed, which was assigned to probe at Co sites. Indication of a Jahn-Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.