Sr<SUB>4</SUB>M<SUB>3</SUB>ReO<SUB>12</SUB> (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 (Tc = &#8764; 250-300 K). While the M = Co phase crystallizes in a partially ordered double perovskite (Fm3m) structure (a = 7.8153 &#197;), the M = Fe phase adopts a primitive cubic perovskite (Pm3m) structure (a = 3.9353 &#197;), 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 Tc. 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