Orbital Ordering of Intermediate-Spin State of Co3+ in Sr3YCo4O10.5

The orbital ordering and spin state in the room-temperature ferromagnet Sr 3 YCo 4 O 10.5 were investigated by a resonant X-ray scattering technique. A resonating signal with a σ→π' scattering component was observed at ( h 00), where h =2 n +1 ( n : integer), near the 1 s → e g transition energy of Co. This provides direct evidence of not only e g orbital ordering but also the existence of the intermediate-spin (IS) state. Moreover, we suggest that the ferrimagnetism is induced by the e g orbital ordering of the IS state of Co 3+ . The peculiar e g orbital, spin-state, and magnetic orderings are also discussed.