MAGNETIC STRUCTURE OF MFePO₅ COMPOUNDS (M = Cu, Ni)

抄録

We have performed a neutron powder diffraction study of the oxyphosphates MFePO₅ (M = Cu, Ni) as a function of temperature. The structure of this allotropic variety is orthorhombic with space-group Pnma. The M^II-octahedra build strings parallel to the b-axis. The Fe^III-octahedra are alternatively connected, on both sides of these strings, by PO₄ tetrahedra. No disorder between metallic sites has been found. Our study confirms the isomorphism of these compounds with α-Fe₂PO₅. We have determined their magnetic structures which are both collinear anti-ferromagnetic with the spin of both sites directed along the b-axis. The experimental magnetic moments of Cu⁺² and Ni²⁺ correspond to the expected ionic value, on the contrary the magnetic moment of Fe³⁺ is reduced.