Neutron Diffraction, M?ssbauer Spectrum, and Magnetic Behavior of Ag2FeMn2(PO4)3 with Alluaudite-like Structure

The new compound Ag2FeMn2(PO4)3 has been synthesized using solid state reactions, and characterized by X-ray and neutron diffraction. It crystallizes in the monoclinic space group C2/c with the parameters a=12.1466(3) ?, b=12.7328(4) ?, c=6.4999(5) ?, and =114.53(3)°. Its structure is formed by [FeMn2O12] chains of edge-sharing FeO6 and MnO6 octahedra. The chains are interconnected by the PO4 tetrahedra giving rise to layers parallel to the ac plane and exhibiting a three-dimensional channel-like structure where the silver cations are located. The distribution of the FeO6 and MnO6 octahedra along the chains was determined by the neutron refinements. The M?ssbauer spectral parameters indicate the presence of only Fe(III) octahedral sites. The reciprocal susceptibility variation shows a deviation from the Curie–Weiss law below 19 K, which can be attributed to a weakly ferromagnetic component owing to probable canting of antiferromagnetically coupled spins along the [FeMn2O12] chains.