Electron doping in the double perovskite La_xA _2-xCrWO₆ with A=Sr and Ca

The ferrimagnetic double perovskites can have high Curie temperatures TC above 600 K. In the system Sr2 FeMoO6 (TC ≈420 K) electron doping by substituting, for example, La3+ for Sr2+ ions leads to a considerable increase in TC. Here we report the same effect for Lax Ca2-x CrWO6. This demonstrates that electron doping generically increases TC in the ferrimagnetic double perovskites. However, in the system Sr2 CrWO6 (TC ≈450 K) the preferential formation of LaCrO3 prevents electron doping by La substitution as supported by neutron scattering and x-ray diffraction.