Structural and magnetic properties of Fe[Fe(CN)₆]·4H₂O

Abstract

We report the structural and magnetic properties of polycrystalline ferriferricyanide, Fe[Fe(CN)₆]·4H₂O. The room temperature neutron diffraction pattern of the sample was refined with space group Fm3m by the Rietveld refinement technique. The Mössbauer spectrum of the sample at room temperature reveals the presence of low spin Fe³⁺(Fe^LS, S = 1/2) and high spin Fe³⁺(Fe^HS, S = 5/2) ions. The compound undergoes a paramagnetic to ferromagnetic phase transition at 17.4 K. Saturation magnetization at 2.3 K corresponds to parallel ordering of FeHS and FeLS spin only moments in Fe[Fe(CN)₆]·4H₂O. Neutron diffraction study at 1.5K shows the ordered site moments of 5.0(2) and 0.8(2)μ_B for Fe^HS and Fe^LS ions, respectively, in Fe^HS[Fe^LS(CN)₆]·4H₂O. The coercive field of the compound is an order of magnitude higher than that of many other compounds in the Prussian Blue analog family. The observed branching between field-cooled and zero field-cooled magnetization below T_C(= 17.4 K) is ascribed due to magnetic domain kinetics under different cooling conditions and the presence of available vacant sites in the lattice for the water molecules.