Magnetic properties of KNaMSi4O10 compounds (M = Mn, Fe, Cu)


In the present work the synthesis and magnetic properties of three compounds with formula KNaMSi4O10 (M = Mn, Fe, Cu) are described. These compounds are synthetic analogs to natural occurring minerals: fenaksite-Fe2+, litidionite-Cu2+ and manaksite-Mn2+. The crystal structure consists of complex silicate chains interconnected by edge-sharing MO5 square pyramids dimerized in M2O8 units. This charged metal-silicate framework is compensated by monovalent alkali metals (K+, Na+). Despite the isostructural nature of these compounds, and the consequent similarity of the M-O topology, that rules the magnetic properties, these are quite different. While there are antiferromagnetic (AF) interactions within the Mn and Cu dimers (exchange interaction J = -3.83(1) and -2.86(3) K, respectively) with no long range order, a ferromagnetic interaction within Fe dimers (J = +7.6(1) K) is observed with a three-dimensional transition at 9K to an AF ground state. The magnetic behaviour is analyzed using the HDVV (Heisenberg-Dirac-Van Vleck) formalism and discussed in the light of the crystal structure. (C) 2008 Elsevier Inc. All rights reserved.



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Brandao, P; Rocha, J; Reis, MS; dos Santos, AM; Jin, R

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Research sponsored by the Laboratory Directed Research and Development Program and the Division of Materials Sciences and Engineering, of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract no. DE-AC05-00OR22725. The authors also thank FCT for the VSM equipment (REEQ/1126/2001). One of the authors (M.S.R.) acknowledges the financial support from the PCI Program during his stay at CBPF.

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