CuSiO3:: A quasi-one-dimensional S=1/2 antiferromagnetic chain system

CuSiO3, isotypic to the spin-Peierls compound CuGeO3, was discovered recently as a metastable decomposition product of the silicate mineral dioptase, Cu6Si6O18 . 6H(2)O. We investigated the physical properties of CuSiO3 using susceptibility, magnetization, and specific heat measurements on powder samples. The magnetic susceptibility chi (T) is reproduced very well above T = 8 K by theoretical calculations for an S = 1/2 antiferromagnetic Heisenberg linear chain without frustration (alpha = 0) and a nearest-neighbor exchange coupling constant of J/k(B) = 21 K, much weaker than in CuGeO3. Below 8 K the susceptibility exhibits a substantial drop. This feature is identified as a second-order phase transition at T-0 = 7.9 K by specific heat measurements. The influence of magnetic fields on To is weak, and ac-magnetization measurements give strong evidence for a spin-flop phase at mu (0)H(SF)similar or equal to3 T. The origin of the magnetic phase transition at T-0= 7.9 K is discussed in the context of long-range antiferromagnetic order (AF) versus spin-Peierls (SP) order, Susceptibility and specific heat results support the AF ordered ground state, Additional temperature dependent Cu-63,Cu-65 nuclear quadrupole resonance experiments have been carried out to probe the Cu2+ electronic state and the spin dynamics in CuSiO3.