Pressure-Induced Magnetic Switching and Linkage Isomerism in K0.4Fe4[Cr(CN)6]2.8·16H2O: X-ray Absorption and Magnetic Circular Dichroism Stu

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• 作者：Eugenio Coronado ; M. Carmen Gime&#769 ; nez-Lo&#769 ; pez ; Tomasz Korzeniak ; Georgiy Levchenko ; Francisco M. Romero ; Alfredo Segura ; Valenti&#769 ; n Garci&#769 ; a-Baonza ; Julio C. Cezar ; Frank M. F. de Groo
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：November 19, 2008
• 年：2008
• 卷：130
• 期：46
• 页码：15519-15532
• 全文大小：473K
• 年卷期：v.130,no.46(November 19, 2008)
• ISSN：1520-5126

文摘

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K_0.4Fe₄[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 (T_C) 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 T_C = 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 Cr^III−CN−Fe^II linkages to the Cr^III−NC−Fe^II 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% Cr^III−NC−Fe^II linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process.