Magnetic properties of multi-metal Prussian Blue analogue Co_0.75Ni_0.75[Fe(CN)₆]·6.8H₂O

Abstract

We have studied magnetic properties of the ternary metal Prussian Blue analogue Co_0.75Ni_0.75[Fe(CN)₆]·6.8H₂O. Room temperature Mössbauer and IR spectra give the evidence of two Fe^III sites in the compound. It undergoes a paramagnetic to ferromagnetic phase transition at 15.9 K. Field dependent magnetization data correspond to a ferromagnetic ordering of the spin only moments of Fe^III, Co^II and Ni^II ions. Approximately 87.45% Fe^III ions are in low spin (S = 1/2) and 12.55% Fe^III ions are in high spin (S = 5/2) state. On the other hand, 100% Co^II ions are in low spin (S = 1/2) and 100% Ni^II ions are in (t₂g)⁶(e_g)² spin state (S = 1). The observed very large coercive field at lower temperatures is an indication of the presence of magnetic hardness in the compound. Non-saturation of magnetization at 1.5 K even under 100 kOe field and a bifurcation in the field cooled and zero field cooled magnetization curves indicate the presence of some spin glass type component in the compound.