Abstract
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 View the MathML source, respectively) with no long range order, a ferromagnetic interaction within Fe dimers View the MathML source is observed with a three-dimensional transition at 9 K to an AF ground state. The magnetic behavior is analyzed using the HDVV (Heisenberg–Dirac–Van Vleck) formalism and discussed in the light of the crystal structure.
Magnetic susceptibility times temperature. The antiferromagnetic arrangement within Mn and Cu dimers is evident (due to the positive derivative at lower temperatures). For the Fe-counterpart a three-dimensional transition to an antiferromagnetic (AF) inter-dimer interaction is found upon cooling. Above this transition the drop in χT is a signature of ferromagnetic intra-dimer interactions.
