Magnetic properties of electrochemically prepared crystalline films of Prussian blue-based molecular magnets K _j Cr^II _k [Cr^III(CN)₆] _l · mH ₂O

Crystalline films (thickness ∼1 μm) of Prussian blue-based molecular magnets, synthesized using electrochemical method at two different reduction potentials -0.5 and -0.9 V, result into K_0.1Cr^II _1.45[Cr^III(CN)₆] · mH₂O (film 1) and K_0.8Cr^II _1.1[Cr^III(CN) ₆] · mH₂O (film 2), respectively. The structural and magnetic properties of such films are investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), infrared (IR) spectroscopy, and dc magnetization measurements. The film morphology, examined using AFM, shows uniformly distributed triangular crystallites over the substrate surface. The presence of Cr^III-C≡N-Cr^II sequence, in the range of 1,900 to 2,300 cm^-1 in IR spectra, confirms formation of Prussian blue analogues. The XRD results reveal information about the crystalline nature of the films and the relative intensities of the Bragg peaks change with the K⁺ ions. The exchange interaction between Cr ions through C≡N ligand confirms that the electron transfer from C≡N molecule to Cr ions is ferrimagnetic in nature. The high Curie temperatures (T _C) are found to be ∼195 and ∼215 K for film 1 and film 2, respectively. The higher value of T _C is attributed to the inclusion of more K⁺ ions for film 2, resulting decreases in the Cr^III(C≡N) ₆ vacancies and increases in the number of nearest neighbors of Cr^II ions. The branching in the zero field-cooled and field-cooled magnetization data below Curie temperature is explained in terms of kinetic behavior of magnetic domains with different cooling conditions and the presence of water molecule vacancies in the lattice.