Charge and Zener polaron order in Bi0.75Sr0.25MnO3

Abstract

We have characterized the RT structure of Bi0.75Sr0.25MnO3 by means of electron diffraction, synchrotron x-ray, and neutron powder diffraction. These data evidence that a;b;A2ap and c;2ap average structure presents a modulation that doubles the a and c lattice parameters. The temperature evolution of this compound above RT has been investigated using magnetization, calorimetry measurements, and neutron powder diffraction. These data reveal that the superstructure disappears above ;575 K where a structural transition takes place. Susceptibility data show that, concomitant to the formation of the superstructure ~on cooling!, there is an enhancement of the effective paramagnetic moment as has also been found in other Bi-(Sr,Ca)MnO3 bismuth manganites. The observed features and cell evolution signals that a new type of charge and polaron ordering occurs at this composition.