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

CaCu2.5Mn4.5O12 perovskite has been prepared in polycrystalline form under moderate pressure conditions of 20 kbar, in the presence of KClO4 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 Im3 (No. 204), with a = 7.2279(1) A at room temperature (RT). In the ABO3 perovskite superstructure, the A positions are occupied by Ca2+ and (Cu2.52+Mn0.53+), 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+; MnO6 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 Mn3.875+ and (Cu2.52+Mn0.53+) spins, with ordered magnetic moments of 2.32(5) and −0.54(3) μB, respectively. An additional canting effect of the Mn moments...