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.