The Role of Order-Disorder Transitions in the Quest for Molecular Multiferroics: Structural and Magnetic Neutron Studies of a Mixed Valence Iron (II)-Iron (III) Formate Framework - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of the American Chemical Society Année : 2012

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

Résumé

Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH2(CH3)2]n[FeIIIFeII(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-disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [FeIIIFeII(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 Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different FeII and FeIII magnetic moments.
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Dates et versions

hal-00941967 , version 1 (04-02-2014)

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Laura Canadillas-Delgado, Oscar Fabelo, J. Alberto Rodríguez-Velamazán, Marie-Hélène Lemée-Cailleau, Sax A. Mason, et al.. The Role of Order-Disorder Transitions in the Quest for Molecular Multiferroics: Structural and Magnetic Neutron Studies of a Mixed Valence Iron (II)-Iron (III) Formate Framework. Journal of the American Chemical Society, 2012, 134, pp.19772. ⟨10.1021/ja3082457⟩. ⟨hal-00941967⟩
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