High spin, hole delocalization and electron transfer in LBaCo₂O_5.5(L Sm, Eu, Gd, Tb, Dy, Y)

Abstract

By means of electron-correlation-corrected density functional calculations for GdBaCoO5.5, it has been found that the pdσ hole delocalization in the 'almost high-spin' state is responsible for the antiferromagnetic–ferromagnetic-like transition and insulator–metal transition in isostructural LBaCo2O5.5 (L = Sm, Eu, Gd, Tb, Dy, Y), and that the simultaneous octahedral Co1 3z2 − r2 /x2 − y2 (pyramidal Co2 x2 − y2) → Co1 (Co2) yz electron transfer gives rise to the lattice anomaly at TIM. The present study, supporting the author's prior work (Wu H 2001 Phys. Rev. B 64 092413), provides a unified explanation for a number of experimental findings for LBaCo2O5.5.