Magnetic and dielectric properties of one-dimensional array of S=1/2 linear trimer system Na2Cu3Ge4O12

Magnetic susceptibility chi, specific heat C, capacitance C-p, and Na-23-NMR measurements have been carried out on polycrystalline samples of quantum spin linear trimer system Na2Cu3Ge4O12, which has the one-dimensional array of Cu3O8 trimers formed of edge-sharing three CuO4 square planes. The exchange interactions between the Cu2+ (S = 1/2) spins have been determined by analyzing chi-T and C-T curves. By employing the isolated S = 1/2 Heisenberg trimer model above 70K, the nearest-neighbor exchange couplings J(1) and the second-neighbor one J(2) in trimer have been evaluated to J(1)/k(B) = 30 +/- 20K (antiferromagnetic) and J(2)/k(B) 340 +/- 20K. At low temperature region, two spins of the edge in the Cu3O8 trimers form a nonmagnetic singlet by strong antiferromagnetic interaction J(2), and the spin left in the center of the Cu3O8 trimer forms one-dimensional chains by the exchange interaction J(3) between the trimers. By employing the S = 1/2 uniform Heisenberg chain model below 70 K, we have evaluated to J(3)/k(B) 18 +/- 1K. The mechanism of multiferroic behavior at T-c 2K is discussed. (C) 2014 AIP Publishing LLC.