Spin-state order/disorder and metal–insulator transition in GdBaCo2O5.5: experimental determination of the underlying electronic structure
oleh: Z Hu, Hua Wu, T C Koethe, S N Barilo, S V Shiryaev, G L Bychkov, C Schüßler-Langeheine, T Lorenz, A Tanaka, H H Hsieh, H-J Lin, C T Chen, N B Brookes, S Agrestini, Y-Y Chin, M Rotter, L H Tjeng
| Format: | Article |
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| Diterbitkan: | IOP Publishing 2012-01-01 |
Deskripsi
We have investigated the electronic structure of GdBaCo _2 O _5.5 across the metal–insulator transition (MIT) using soft x-ray absorption and photoelectron spectroscopy. For the low-temperature insulating phase, we find that half of the Co ^3+ ions at the octahedral sites are in the low spin (LS) and the other half in the high spin (HS) state, while the Co ^3+ ions at the pyramidal sites are in the HS configuration. Upon increasing the temperature across the MIT, part of the LS octahedral Co ^3+ undergoes a spin-state transition into the HS configuration. We infer that this destroys the spin-state ordering and thus explains the decrease in resistivity. We observed that the band gap is reduced but not closed in the high-temperature phase.