Effect of Cu2+ (S= 1/2 ) substitution on the antiferromagnetic ordered phases Co2(OH)XO4 (X = P, As)

The isostructural Co1.5Cu0.5(OH)(XO4) (X = P, As) phases have been prepared from hydrothermal synthesis and characterized from powder X-ray diffraction. The structure consists of a three-dimensional framework in which M(1)O5-trigonal bipyramid dimers and M(2)O6-octahedral chains M = (Cu and Co) are simultaneously present. Magnetization measurements of Co1.5Cu0.5(OH)(PO4) show the presence of one maxima at ca. 60 K attributed to a three-dimensional antiferromagnetic ordering. This behaviour was confirmed from the ac measurements. Below TN, a significant irreversibility appears in ZFC-FC measurements suggesting the presence of some ferromagnetic contributions. When PO43- is substituted by AsO43- anions, the irreversibility exhibited for the Co-Cu hydroxi-phosphate disappears showing a broad maximum around 44 K accompanied by a large decrease below this temperature.