Synthesis, crystal structure and magnetic behavior of a new calcium magnesium and iron orthophosphate Ca2MgFe2(PO4)

The structure of the new calcium magnesium iron orthophosphate, Ca2MgFe2(PO4)(4) was determined from single crystal X-ray diffraction data. It crystallizes in the orthorhombic system, space group Pbca, with all atoms in general positions among which two sites are disordered. The crystal structure of this phosphate is build up from PO4 tetrahedra linked to FeO6 octahedra and to (Fe/Mg)O-5 polyhedra via common vertices. In fact, each of the two mixed sites (Fe/Mg) is surrounded by five oxygen atoms which form either a pyramid with a square base or a bi-pyramid with a triangular base. The interconnection of these polyhedra leads to a three-dimensional structure delimiting cavities where Ca2+ cations are localized. The powder of this compound was successfully obtained by solid state reaction and its X-ray diffraction diagram was refined by pattern matching method. The magnetic measurements show multiple transition assigned to frustrated triangles locally present in AFM (antiferromagnetic) magnetic layered units.