resumo
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.
palavras-chave
CRYSTAL-STRUCTURE; COMPLEXES; TRANSITION; DIMER
categoria
Chemistry
autores
Brandao, P; Rocha, J; Reis, MS; dos Santos, AM; Jin, R
nossos autores
João Rocha
Prof. Catedrático
Mário de Souza Reis Junior
Investigador
Paula Cristina Ferreira da Silva Brandão
Investigador Auxiliaragradecimentos
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.