Effect of preparation procedure on the magnetic and transport properties of double perovskite Sr₂FeMoO₆

Ordered and disordered double perovskite Sr_2FeMoO_6 ceramics have been investigated by powder x-ray diffraction, magnetic and transport measurements, as well as M?ssbauer spectroscopy. The heavily disordered sample can be acquired by annealing the ordered samples in argon. The annealing procedure affects not only the nature of grain boundaries but also the grain itself. The evidence of M?ssbauer spectra performed at 77 and 300 K indicates that there exist small oxygen deficient clusters of SrFeO_3-y in the disordered sample. The paramagnetic Fe^4+ and Fe^3+ ions in the compound subsist down to 77 K and the ratio of Fe^4+/Fe^3+ increases with decreasing temperature.