Influence of CoO bond length on the spin state of Co in cobaltite perovskites RCoO3 (R = Y, Ho)

Abstract

A comparative study of the electronic structure and magnetic properties of YCoO3 and HoCoO3 has been carries out using ab initio density-functional calculations with local spin density approximation (LDSA) and LSDA + U methods. It is found that YCoO3 shows nonmagnetic (spin S=0) insulator character below 600 K and an electronic transition of Co3+ ions from a low spin (LS) state to a high-spin (HS) state above 600 K. In contrast, HoCoO3 shows nonmagnetic property with Co ions in a LS state over a wide temperature range (300-995 K). The intermediate-spin (IS) state becomes more stable than the LS state only a temperature of 1098 K in HoCoO3. We suggest that the variation of Co-O bond length induced by the unit cell expansion may play an-important role in the evolution of the spin state of Co3+ with increasing temperature in these perovskite cobalt oxides. The discrepancy of the averaged Co-O bond length in YCoO3 and HoCoO3 may be a likely reason for the difference of electronic properties between them. The decrease of the Co-O bond length could result in stabilization of the LS state. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim