Neutron diffraction, Mossbauer spectrum, and magnetic behavior of Ag2FeMn2(PO4)(3) with alluaudite-like structure

The new compound Ag2FeMn2(PO4)(3) has been synthesized using solid state re actions, and characterized by X-ray and neutron diffraction, It crystallize s in the monoclinic space group C2/c with the parameters a 12.1466(3)Angstr om, b=12.7328(4)Angstrom, c = 6.4999(5)Angstrom, and beta = 114.53(3)degree s Its structure is formed by [FeMn2O12](infinity) chains of edge-sharing Fe O6 and MnO6 octahedra. The chains are interconnected by the PO4 tetrahedra giving rise to layers parallel to the ac plane and exhibiting a three-dimen sional channel-like structure where the silver cations are located. The dis tribution of the FeO6 and MnO6 octahedra along the chains was determined by the neutron refinements. The Massbauer spectral parameters indicate the pr esence of only Fe(III) octahedral sites. The reciprocal susceptibility vari ation shows a deviation from the Curie-Weiss law below 19 K, which can be a ttributed to a weakly ferromagnetic component owing to probable canting of antiferromagnetically coupled spins along the [FeMn2O12](infinity) chains. (C) 2001 Academic Press.