Disclosing the origin of the reduced magnetoresistance in electron-doped double perovskites

Electron doping in A2-xLxFeMoO6 (where L is a trivalent lanthanide and A is a divalent cation) double perovskites has been established as a suitable technique for increasing their Curie temperature. However, it was found that the magnetoresistance gradually decreases with increasing lanthanide substitution. Here we analyse in detail the magnetoresistance as a function of the magnetic field for several series of ceramic A2-xLxFeMoO6 oxides, showing that the data can be well described by assuming a gradual loss of spin polarization of the conduction band upon electron doping. This observation introduces some constraints to models of ferromagnetic coupling in double perovskites.