Spin orders in the charge disproportionated phases of A-site layer ordered triple perovskite LaCa2Fe3O9
Résumé
The coupling between spins and charge disproportionation states has been investigated in the LaCa 2 Fe 3 O 9 oxide with neutron powder diffraction. This A-site layer ordered triple perovskite LaCa 2 Fe 3 O 9 undergoes charge disproportionation on cooling and shows two different charge ordering patterns. At 230 K, Fe 3.67+ disproportionates into a 2:1 ratio of Fe 3+ :Fe 5+ which order in a layered manner along the <010> direction of the pseudocubic unit cell. At lower temperatures (T < 170 K), the charge ordering pattern changes to a layered arrangement along the <111> direction. Neutron powder diffraction data shows that in the intermediate temperature range (170 K < T < 230 K) the spins order into a cycloidal structure on the ac plane for the Fe 3+ cations while the Fe 5+ cations remain paramagnetic. For the lowest temperature range (2 K < T < 190 K), the spin structure follows the charge ordering and evolves to a <111> layered magnetic structure. Introduction.
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