Low to High Spin-State Transition Induced by Charge Ordering in Antiferrimagnetic YBaCo2O5

Abstract

The oxygen-deficient double perovskite YBaCo 2 O 5 , containing corner-linked CoO 5 square pyramids as principal building units, undergoes a paramagnetic to antiferromagnetic spin ordering at 330 K. This is accompanied by a tetragonal to orthorhombic distortion. Below 220 K orbital ordering and long-range Co 2 + / Co 3 + charge ordering occur as well as a change in the Co 2 + spin state from low to high spin. This transition is shown to be very sensitive to the oxygen content of the sample. To our knowledge this is the first observation of a spin-state transition induced by long-range orbital and charge ordering. © 2000 American Physical Society