Magnetoresistance in ordered and disordered double perovskite oxide,   Sr$_2$FeMoO$_6$
  We have prepared crystallographically ordered and disorder specimens of the double perovskite, Sr$_2$FeMoO$_6$ and investigated their magnetoresistance behaviour. The extent of ordering between the Fe and Mo sites in the two samples is determined by Rietveld analysis of powder x-ray diffraction patterns and reconfirmed by M\"{o}ssbauer studies. While the ordered sample exhibits the sharp low-field response, followed by moderate changes in the magnetoresistance at higher fields, the disordered sample is characterised by the absence of the spectacular low-field response. We argue that the low field response depends crucially on the half-metallic ferromagnetism, while the high-field response follows from the overall magnetic nature of the sample, even in absence of the half-metallic state. 
D. D. Sarma (1), E.V. Sampathkumaran (2), Sugata Ray (1), R.   Nagarajan(2), Subham Majumdar(2), Ashwani Kumar(1), G. Nalini...