The crystal structure and magnetic properties for the ordered double perovskite oxides Sr 2− x K x FeMoO 6 (0 ≤ x ≤ 0.04) are investigated. X-ray powder diffraction studies reveal that all the samples are single phase and have the I4/m symmetry. The anti-site defect (AS) in double perovskite oxides of Sr 2− x K x FeMoO 6 may be adjusted by alkali metal element of K doping. The unit cell magnetization at 280 K is 1.12 μ B for x = 0 and 1.26 μ B for x = 0.04, respectively. The cation-ordering and the Fe O(1) Mo bond-angle play the competition roles on the magnetism in the doping system.
