MAGNETIC SUSCEPTIBILITY FOR THE Cu2-II-IV-S4 (II=Mn, Fe; IV=Si, Ge or Sn) COMPOUNDS: EXCHANGE INTERACTION PARAMETERS

Measurements of magnetic susceptibility χ as a function of temperature (from 2 to 300 K) were made on polycrystalline samples of the compounds Cu2MnSiS4, Cu2MnGeS4, Cu2MnSnS4, Cu2FeSiS4 and Cu2FeGeS4. From the 1/ χ versus T curves, it was concluded that the samples were antiferromagnetic. These curves were also used to determine values of the Neel temperature TN and the Curie-Weiss temperature θ for each compound. When the values of TN and θ are plotted against its molecular weight W, it was found that the compounds containing Mn lie on the same straight line, while those with Fe lie on a different one. For each compound, an analysis was carried out in terms of the simple mean-field theory and using the virtual transition model of Geertsma et al. for exchange interaction, and values of exchange interaction parameters were determined from the measured TN and θ data.