Preparation, Crystal and Magnetic Structure, and Magnetotransport Properties of the Double Perovskite CaCu2.5Mn4.5O12

CaCu 2.5 Mn 4.5 O 12 perovskite has been prepared in polycrystalline form under moderate pressure conditions of 20 kbar, in the presence of KClO 4 as oxidizing agent. This material has been studied by X-ray and neutron powder diffraction (NPD), magnetic, magnetotransport, and thermopower measurements. The crystal structure is cubic, space group Im 3̄ (No. 204), with a = 7.2279(1) Å at room temperature (RT). In the ABO 3 perovskite superstructure, the A positions are occupied by Ca 2+ and (Cu 2.5 2+ Mn 0.5 3+ ), ordered in a 1:3 arrangement giving rise to the body-centering of the unit cell. At the B positions, Mn adopts a mixed oxidation state of 3.875+; MnO 6 octahedra are considerably tilted by 19°, due to the relatively small size of the A-type cations. The Curie temperature is 345 K. Low temperature (2 K) NPD data show evidence for a ferrimagnetic coupling between Mn 3.875+ and (Cu 2.5 2+ Mn 0.5 3+ ) spins, with ordered magnetic moments of 2.32(5) and −0.54(3) μ B, respectively. An additional canting effect of the Mn moments at B positions has been detected below 70 K, breaking down the body centered symmetry. We have developed a microscopic model that explains both the saturation magnetization values and the refined magnetic moments at A and B positions. Our results show that Cu 2+ and Mn 3+ spins at the A substructure are almost perpendicular to each other. A magnetoresistance (MR) of 34% has been observed at 5 K for H = 9 T; the low field MR at RT is as high as 2% and shows an appreciable temperature stability.