Structural, electronic and magnetic properties of the series of double perovskites (Ca,Sr) sub(2-x)La sub(x)FeIrO sub(6)(Ca,Sr)2 -xLaxFeIrO6

Polycrystalline samples of the series of double perovskites Sr sub(2-x)La sub(x)FeIrO sub(6)Sr2-xL axFeIrO6 were synthesized. Their structural, electronic and magnetic properties were investigated by X-ray powder diffraction, Mossbauer spectroscopy, magnetic susceptibility, heat capacity and electrical resistivity experiments. The compounds crystallize in a monoclinic structure and were fitted in space group P2 sub(1)/nP21/n, with a significant degree of Fe/Ir cationic disorder. As in Ca sub(2-x)La sub(x)FeIrO sub(6)Ca2-xL axFeIrO6 the Sr-based system seems to evolve from an antiferromagnetic ground state for the end members (x=0.0 and x=2.0) to a ferrimagnetic order in the intermediate regions (x~1x~1). Since Mossbauer spectra indicate that Fe valence remains 3+ with doping, this tendency of change in the nature of the microscopic interaction could be attributed to Ir valence changes, induced by La super(3+) electrical doping. Upon comparing both Ca and Sr series, Sr sub(2-x)La sub(x)FeIrO sub(6)Sr2-xL axFeIrO6 is more structurally homogenous and presents higher magnetization and transition temperatures. Magnetic susceptibility measurements at high temperatures on Sr sub(1.2)La sub(0.8)FeIrO sub(6)Sr1.2La0.8FeIrO6 indicate a very high ferrimagnetic Curie temperature TC~700K. For the Sr sub(2)FeIrO sub(6) compound, electrical resistivity experiments under applied pressure suggest that this material might be a Mott insulator.