Magnetic Orderings in Li sub(2)Cu(WO sub(4)) sub(2) with Tungstate-Bridged Quasi-1D Spin-1/2 Chains

By both experimental measurements and theoretical calculations, we investigated the magnetic and electronic properties of Li sub(2)Cu(WO sub(4)) sub(2) as a tungstate-bridged quasi-one-dimensional (1D) copper spin-(1/2) chain system. Interestingly, magnetic susceptibility chi (T) and specific heat measurements show that the system undergoes a three-dimensional antiferromagnetic (AF)-like ordering at T sub(N) [asymptotically =] 3-7 K, below a broad chi (T) maximum at ~8.9 K indicating a low-dimensional short-range AF spin correlation. Bonner-Fisher model fitting of chi (T) leads to an AF intrachain exchange constant of J/k sub(B) = 15.8 + or - 0.1 K, and mean-field theory estimation gives an interchain coupling constant of J sub([perpendicular])/k sub(B) = 1.6 K, which supports the quasi-1D nature of this spin system. Theoretical evaluation of exchange coupling constants within the generalized gradient approximation (GGA) plus on-site Coulomb interaction (U) shows that the dominant AF exchange interaction is of ~13.9 K along the a-axis with weak interchain coupling, in agreement with the experimental result of a quasi-1D spin-(1/2) chain system. The GGA+U calculations also predict that Li sub(2)Cu(WO sub(4)) sub(2) is a charge transfer-type AF semiconductor with a direct band gap of 1.5 eV.