Lifting the geometric frustration through a monoclinic distortion in ¡°114¡± YBaFe₄O_7.0: Magnetism and transport

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• 作者：V. Duffort ; T. Sarkar ; V. Caignaert ; V. Pralong ; B. Raveau ; M. Avdeev ; A. Cervellino ; J.C. Waerenborgh ; E.V. Tsipis
• 关键词：&ldquo ; 114&rdquo ; Iron oxides ; Mode crystallography ; Magnetic structure ; Transport properties
• 刊名：Journal of Solid State Chemistry
• 出版年：2013
• 出版时间：September, 2013
• 年：2013
• 卷：205
• 期：Complete
• 页码：225-235
• 全文大小：4494 K

文摘

The possibility to lift the geometric frustration in the ¡°114¡± stoichiomeric tetragonal oxide YBaFe₄O_7.0 by decreasing the temperature has been investigated using neutron and synchrotron powder diffraction techniques. Besides the structural transition from tetragonal to monoclinic symmetry that appears at T_S=180 K, a magnetic transition is observed below T_N=95 K. The latter corresponds to a lifting of the 3D geometric frustration toward an antiferromagnetic long range ordering, never observed to date in a cubic based ¡°114¡¯¡± oxide. The magnetic structure, characterized by the propagation vector k₁=(0,0,?), shows that one iron Fe2 exhibits a larger magnetic moment than the three others, suggesting a possible charge ordering according to the formula The magnetic M(T) and ¦Ö¡ä(T) curves, in agreement with neutron data, confirm the structural and magnetic transitions and evidence the coexistence of residual magnetic frustration. Moreover, the transport measurements show a resistive transition from a thermally activated conduction mechanism to a variable range hopping mechanism at T_S=180 K, with a significant increase of the dependence of the resistivity vs. temperature. M?ssbauer spectroscopy clearly evidences a change in the electronic configuration of the iron framework at the structural transition as well as coexistence of several oxidation states. The role of barium underbonding in these transitions is discussed.