Structural, electronic and magnetic properties of the series of double perovskites (Ca, Sr)_2-x^LaxFeIrO⁶

Polycrystalline samples of the series of double perovskites Sr2 _-x^LaxFeIrO6 were synthesized. Their structural, electronic and magnetic properties were investigated by X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, heat capacity and electrical resistivity experiments. The compounds crystallize in a monoclinic structure and were fitted in space group P2₁/n, with a significant degree of Fe/Ir cationic disorder. As in Ca2_-x ^LaxFeIrO6 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∼1). Since Mössbauer 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 La³⁺ electrical doping. Upon comparing both Ca and Sr series, Sr2_-x^LaxFeIrO6 is more structurally homogenous and presents higher magnetization and transition temperatures. Magnetic susceptibility measurements at high temperatures on ^{Sr1.2La0.8FeIrO6} indicate a very high ferrimagnetic Curie temperature ^TC∼700K. For the Sr ₂FeIrO₆ compound, electrical resistivity experiments under applied pressure suggest that this material might be a Mott insulator.