Sr₄M₃ReO₁₂ (M = Co, Fe): New Ferromagnetic Perovskite Oxides

We describe the synthesis, structure, and magnetic properties of two new perovskite oxides, Sr₄M₃ReO₁₂ (M = Co, Fe), that exhibit ferromagnetism with fairly high ordering temperatures (T_c = ∼250−300 K). While the M = Co phase crystallizes in a partially ordered double perovskite (Fm3̅m) structure (a = 7.8153 Å), the M = Fe phase adopts a primitive cubic perovskite (Pm3̅m) structure (a = 3.9353 Å), where the transition metal atoms are not ordered in the long range. Magnetization studies revealed bulk ferromagnetism for both oxides, but the disordered structures seem to preclude a long-range magnetic order and a definite T_c. While further studies are needed to establish the exact origin of magnetism of these materials, the present investigation reveals the possibility of designing new ferromagnetic oxides based on M³⁺−O−Re⁷⁺ (M = Co, Fe) magnetic interaction in the perovskite related structures.