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

We report the structural and magnetic properties of polycrystalline ferriferricyanide, $\mathrm{Fe}[\mathrm{Fe}{(\mathrm{C}\mathrm{N})}_{6}]∙4{\mathrm{H}}_{2}\mathrm{O}$. The room temperature neutron diffraction pattern of the sample was refined with space group $Fm3m$ by the Rietveld refinement technique. The M\"ossbauer spectrum of the sample at room temperature reveals the presence of low spin ${\mathrm{Fe}}^{3+}\phantom{\rule{0.3em}{0ex}}({\mathrm{Fe}}^{\mathrm{LS}},\phantom{\rule{0.3em}{0ex}}S=1∕2)$ and high spin ${\mathrm{Fe}}^{3+}\phantom{\rule{0.3em}{0ex}}({\mathrm{Fe}}^{\mathrm{HS}},\phantom{\rule{0.3em}{0ex}}S=5∕2)$ ions. The compound undergoes a paramagnetic to ferromagnetic phase transition at $17.4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Saturation magnetization at $2.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ corresponds to parallel ordering of ${\mathrm{Fe}}^{\mathrm{HS}}$ and ${\mathrm{Fe}}^{\mathrm{LS}}$ spin only moments in $\mathrm{Fe}[\mathrm{Fe}{(\mathrm{C}\mathrm{N})}_{6}]∙4{\mathrm{H}}_{2}\mathrm{O}$. Neutron diffraction study at $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ shows the ordered site moments of 5.0(2) and $0.8(2)\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ for ${\mathrm{Fe}}^{\mathrm{HS}}$ and ${\mathrm{Fe}}^{\mathrm{LS}}$ ions, respectively, in ${\mathrm{Fe}}^{\mathrm{HS}}[{\mathrm{Fe}}^{\mathrm{LS}}{(\mathrm{C}\mathrm{N})}_{6}]∙4{\mathrm{H}}_{2}\mathrm{O}$. 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 ${T}_{C}\phantom{\rule{0.3em}{0ex}}(=17.4\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ 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.