Samples of La0.6Sr0.4Fe3-δ with varying oxygen vacancy contents were prepared by heating them in different gas flows. Magnetization measurement showed that samples with low oxygen vacancies have a magnetic ordering temperature in the range of 300-325 K while those with 9%-12% oxygen vacancies have a magnetic ordering temperature of 800 K and higher. Mössbauer spectra at 300 K exhibit paramagnetic or weak magnetic characteristics for the N2, O2, and air-quenched samples, whereas an average hyperfine field of 52 T is found for the CO/CO2 reduced samples. The heat treatment in the reducing atmosphere creates oxygen vacancies and increases unit cell volume. However, the Fe-O bond length remains nearly constant, resulting in distortion/rotation of the oxygen octahedra which increases the Fe-O-Fe bond angle as much as 12 degrees. This dramatically affects the Fe-O-Fe superexchange coupling and plays a key role in the increase of the Nèel temperatures.
J. Yang et al., "Magnetic and Mössbauer Studies on Oxygen Deficient Perovskite, La₀.₆Sr₀.₄FeO3-δ," Journal of Applied Physics, vol. 91, no. 10, pp. 7718-7720, American Institute of Physics (AIP), May 2002.
The definitive version is available at https://doi.org/10.1063/1.1446128
Materials Science and Engineering
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© 2002 American Institute of Physics (AIP), All rights reserved.
15 May 2002