Local iron ion distribution and magnetic properties of the perovskites La1-xSrxFeO3-γ.

The influence of thermal annealing on the structural and magnetic properties of nanocrystalline La1-xSrxFeO3-γ perovskites with x=0, 0.3, 0.4 and 0.5 was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy and magnetization measurements. Samples prepared by a sol gel method were calcined for 4 h at 1073 K and annealed for 8 h at 1273 K. XRD data indicate the formation of single phases in all samples, orthorhombic with the space group Pbnm for x = 0.0 and 0.3 and rhombohedral with the space group R3‾c for x = 0.4 and 0.5. The Mössbauer spectroscopy reveal that the sintering process increase the amount of Fe4+ and decrease the paramagnetic sites. Despite of the XRD data indicating the samples to be single phase, the higher coercivity observed in the samples with x = 0.4 may be associated with the emergence of Sr1-xLaxFe12O19 clusters in the samples. Irreversibility in the measurements of magnetization as a function of temperature was interpreted in terms of a high temperature glass cluster behavior.