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|Type:||Artigo de evento|
|Title:||Electronic Changes Related To The Metal-to-insulator Phase Transition In Rnio3|
|Abstract:||Rare earth nickel oxide perovskites (RNiO3, R=rare earth) have, except for LaNiO3, a metal-insulator (MI) phase transition as temperature decreases. The transition temperature (TMI) increases as the R-ion becomes smaller. They present also, at low temperatures, a complex antiferromagnetic order. For lighter R-ions (e.g. Pr and Nd), the antiferromagnetic transition temperature (TN) is close to TMI, while for heavier R-ions (e.g. Eu, Sm), TMI and TN are very far apart, suggesting that the magnetic and electronic behaviors are not directly coupled. Although RNiO3 perovskites are placed in the boundary of the Mott-Hubbard and charge transfer regimes, there are several evidences pointing to a charge transfer gap, mainly controlled by ligand-to-metal charge transfer energy, and thus strongly dependent on hybridization. Ni L-edge absorption spectroscopy (transition 2p → 3d) gives direct information on the density of Ni 3d empty states, and in particular on the multiplet splitting and hybridization between Ni3d and O2p bands. Here we present Ni L3 and L2 absorption spectra measured for NdNiO3 and EuNiO3 (TMI = 200 and 480 K). At room temperature, dramatic differences are observed between EuNiO3 (insulating) and NdNiO3 (metallic). The normalized spectra give evidence for a higher density of 3d unoccupied states and a larger multiplet splitting in EuNiO3. Both effects might be correlated to a decrease in hybridization. The same behavior is observed for NdNiO3 as it is cooled down to the insulating phase (T < 200 K), revealing that in these compounds the opening of the gap is directly related to the degree of hybridization.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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