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This article focuses on electrochemical tuning of the magnetic phase transition. The ability of certain molecules and molecule-based materials to change the nature of their electronic ground state under the presence of an external perturbation is well-known. This leads to functional materials in which a physical property (absorption of light, magnetic moment, electrical conductivity, can be tuned through the application of an external stimulus. abundant in the literature on spin crossover compounds. Less common is the observation of this behavior in magnetically ordered molecule-based materials.

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 · 16H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (Tc) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching Tc = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mössbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some CrIIICNFeII linkages to the CrIIINCFeII form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% CrIIINCFeII linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process. [ABSTRACT FROM AUTHOR]