Structural and magnetic properties ofFe[Fe(CN)6]∙4H2O

Abstract

We report the structural and magnetic properties of polycrystalline ferriferricyanide, $\mathrm{Fe}\left[\mathrm{Fe}{\left(\mathrm{C}\mathrm{N}\right)}_6\right]\bullet 4{\mathrm{H}}_2\mathrm{O}$. 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 ${\mathrm{Fe}}^{3+}({\mathrm{Fe}}^{\mathrm{LS}},S=1∕2)$ and high spin ${\mathrm{Fe}}^{3+}({\mathrm{Fe}}^{\mathrm{HS}},S=5∕2)$ ions. The compound undergoes a paramagnetic to ferromagnetic phase transition at $17.4\mathrm{K}$. Saturation magnetization at $2.3\mathrm{K}$ corresponds to parallel ordering of ${\mathrm{Fe}}^{\mathrm{HS}}$ and ${\mathrm{Fe}}^{\mathrm{LS}}$ spin only moments in $\mathrm{Fe}\left[\mathrm{Fe}{\left(\mathrm{C}\mathrm{N}\right)}_6\right]\bullet 4{\mathrm{H}}_2\mathrm{O}$. Neutron diffraction study at $1.5\mathrm{K}$ shows the ordered site moments of 5.0(2) and $0.8\left(2\right){\mu }_B$ for ${\mathrm{Fe}}^{\mathrm{HS}}$ and ${\mathrm{Fe}}^{\mathrm{LS}}$ ions, respectively, in ${\mathrm{Fe}}^{\mathrm{HS}}\left[{\mathrm{Fe}}^{\mathrm{LS}}{\left(\mathrm{C}\mathrm{N}\right)}_6\right]\bullet 4{\mathrm{H}}_2\mathrm{O}$. 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 $T_C(=17.4\mathrm{K})$ 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.