Molten-Salt-Mediated Syntheses of Sr₂FeReO₆, Ba₂FeReO₆, and Sr₂CrReO₆: Particle Sizes, B/B′ Site Disorder, and Magnetic Properties

The half-metallic double-perovskites Sr₂FeReO₆, Ba₂FeReO₆, and Sr₂CrReO₆ were synthesized in high purity and homogeneity using a NaCl/KCl molten flux at 750–800 °C in as little as 3–6 h. The particle sizes could be varied from ∼50 nm to >1 μm depending on the specific flux conditions and the double-perovskite composition. Powder X-ray diffraction refinements were used to characterize the extent of B/B′ site disorder (i.e., Fe/Re or Cr/Re sites), and that ranged from ∼83–85% for Sr₂FeReO₆, ∼90–97% for Ba₂FeReO₆, and ∼84–90% for Sr₂CrReO₆. The magnetic properties were measured as a function of magnetic field strength and analyzed with respect to the extent of B/B′ site ordering and resultant particle sizes that ranged from ∼50–500 nm for Sr₂FeReO₆, ∼100–800 nm for Sr₂CrReO₆, and ∼250 nm to 2 μm for Ba₂FeReO₆. Further, large temperature-dependent magnetoresistivites were observed for the flux-prepared Sr₂FeReO₆, Ba₂FeReO₆, and Sr₂CrReO₆, which are attributed to high concentrations of grain boundaries present.