Large low-field magnetoresistance and TC in polycrystalline (Ba0.8Sr0.2)2−xLaxFeMoO6 double perovskites

Large low-field magnetoresistance (LFMR) together with high Curie temperatures (TC) are requirements for some applications in magnetoelectronics. In order to optimize both parameters, we have investigated double perovskites (Ba0.8Sr0.2)2−xLaxFeMoO6 (0⩽x⩽0.4). High-temperature neutron diffraction measurements indicate a strong increase in TC with La doping (from ≈345 K for x=0 to ≈405 K for x=0.4). The LFMR is very large for x=0 (at 10 KOe≈27% at 10 K and ≈7% at 290 K) and decreases with La doping. This decrease cannot be attributed to a substantial enhancement of Fe/Mo antisite disorder, which is small as tracked by means of x-ray and high-resolution neutron diffraction, but to grain boundaries modifications.