The Role of Order鈥揇isorder Transitions in the Quest for Molecular Multiferroics: Structural and Magnetic Neutron Studies of a Mixed Valence Iron(II)鈥揑ron(III) Formate Framework

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• 作者：Laura Ca帽adillas-Delgado ; Oscar Fabelo ; J. Alberto Rodr铆guez-Velamaz谩n ; Marie-H茅l猫ne Lem茅e-Cailleau ; Sax A. Mason ; Emilio Pardo ; Francesc Lloret ; Jiong-Peng Zhao ; Xian-He Bu ; Virginie Simonet ; Claire V. Colin ; Juan Rodr铆guez-Carvajal
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：December 5, 2012
• 年：2012
• 卷：134
• 期：48
• 页码：19772-19781
• 全文大小：557K
• 年卷期：v.134,no.48(December 5, 2012)
• ISSN：1520-5126

文摘

Neutron diffraction studies have been carried out to shed light on the unprecedented order鈥揹isorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)鈥搃ron(III) formate framework compound [NH₂(CH₃)₂]_n[Fe^IIIFe^II(HCOO)₆]_n. The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order鈥揹isorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe^IIIFe^II(HCOO)₆]_n framework. In the low-temperature phase, a change in space group from P3̅1c to R3̅c occurs, involving a tripling of the c-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this N茅el N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe^II and Fe^III magnetic moments.