Magnetic properties of Sr_2Fe_1+xMo_1-xO_6 with -1 <= x <= 0.25

We have synthesized the solid solution, Sr_2Fe_1+xMo_1-xO_6 with -1 <= x <= 0.25, the composition x = 0 corresponding to the well-known double perovskite system Sr2FeMoO6. We report structural and magnetic properties of the above system, exhibiting systematic variations across the series. These results restrict the range of models that can explain magnetism in this family of compounds, providing an understanding of the magnetic structure.