By means of high resolution neutron powder diffraction at low temperature we have characterized the structural details of ${\mathrm{La}}_x{\mathrm{Sr}}_{2-x}{\mathrm{FeMoO}}_6$ $(0\mathrm{}<~\mathrm{x}<~0.5)$ and ${\mathrm{Ca}}_x{\mathrm{Sr}}_{2-x}{\mathrm{FeMoO}}_6$ $(0\mathrm{}<~x<~0.6)$ series of compounds. This study reveals a similar variation of the mean bond-angle $〈{\theta }_{\mathrm{Fe}-\mathrm{O}-\mathrm{Mo}}〉$ in both series. In contrast, the mean bond-distance $〈d_{(\mathrm{Fe},\mathrm{Mo})-\mathrm{O}}〉$ increases with La but not with Ca substitution. Both series also present a different evolution of the Curie temperature ${(T}_C),$ which raises in the La series and slightly decreases in the Ca one. We thus conclude that the enhancement of $T_C$ in the La series is due to the electron filling of the conduction band and a concomitant rising of the density of states at the Fermi level.

• Received 10 April 2003

DOI:https://doi.org/10.1103/PhysRevB.68.012412