Probing and comparing electron doping and miss-site effects in Re-based double perovskites.

We have studied the Sr(2-x)La(x)Fe(1+x/2)Re(1-x/2)O(6) series in order to check how the increase in the number of Fe-O-Fe superexchange interactions affects the magnetic properties of this family of double perovskites. In these compounds the addition of La(3+) can be compensated by an increase of the Fe(3+) ratio leading to a non-electron-doped system. The unit cell of these samples expands on replacing Sr by La and the cationic ordering disappears for x>1 samples. Spontaneous magnetization at 5 K is observed in a wide range of concentrations but the magnetization at 5 T decreases as the La content increases. This result may be explained in terms of a ferrimagnetic ground state of the double perovskite. The magnetic ordering temperature increases with increasing the La and Fe content in agreement with an increase in the number of Fe-O-Fe interactions. The comparison to the electron-doped samples suggests that this effect is not enough to explain on its own the stronger T(C)-rise in Sr(2-x)La(x)FeReO(6) compounds.