Statut | Confirmé |
Série | SEM-BESSON |
Domaines | cond-mat |
Date | Mardi 16 Octobre 2012 |
Heure | 10:30 |
Institut | IMPMC |
Salle | salle de conférence 4-etage,couloir 22-23 UPMC, 4 Place Jussieu |
Nom de l'orateur | Takano |
Prenom de l'orateur | Mikio |
Addresse email de l'orateur | |
Institution de l'orateur | Institute for Integrated Cell-Material Sciences Kyoto University |
Titre | Bafeo3, a ferromagnetic iron oxide |
Résumé | A small class of oxides containing iron in a high valence state of Fe4+ (d4) has been known. The most representative phase is SrFeO3 (SFO) crystallizing in the cubic perovskite structure (a = 3.850 Å). SFO and related oxides behave very differently from Fe2+- and Fe3+-oxides like FeO, Fe3O4, and LaFeO3 (LFO). All these Fe2+- and Fe3+-oxides are antiferromagnetic (or ferrimagnetic) insulators in their ground states, while the Fe4+-oxides commonly exhibit a shift toward metallicity and ferromagnetism. The specificity of Fe4+-oxides can be assigned to the fact that the effective charge transfer energy, Δeff, drastically drops from ~8eV for FeO and ~5.5eV for LFO to ~-3eV for SFO. The characteristics of Fe4+-oxides should thus result from interplay of Fe d electrons and O p holes. Very recently we succeeded in preparing BaFeO3 (BFO) crystallizing in the cubic perovskite structure (a = 3.97106(1) Å). Physical characterization revealed that BFO has a spiral spin structure of the A-type below 111K but turns ferromagnetic with a large atomic moment of 3.5 μB/Fe on application of a small external field of ~0.3 T at 5 K (0.2 T at 77K). BFO is the very first Fe-oxide that shows ferromagnetism at ambient pressure. The magnetic transition temperature increases from 111K to more than 300K up to 40GPa. |
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