Magnetic properties ofCu6Ge6O18

Abstract

We studied magnetic properties of powder samples of Cu 6 Ge 6 O 18 -xH 2 O (xϭ0 -6). Susceptibility above the antiferromagnetic ͑AF͒ transition temperature (T N ) agrees with susceptibility obtained from the onedimensional Heisenberg Sϭ1/2 model with competing AF interactions. Since the estimated ratio ͑0.27-0.31͒ between nearest-neighbor and next-nearest-neighbor AF exchange interactions is close to a critical value ͑0.24 -0.30͒ which determines whether a spin gap exists or not, the spin system in Cu 6 Ge 6 O 18 -xH 2 O is probably located near a boundary between spin systems with gapless and gapped magnetic excitation. The value of T N /T max , where T max is the temperature at which the susceptibility is maximum, shows a unique dependence on x. We speculate that a spin gap due to competing AF interactions exists at xϽ1.54 and that magnetic excitation is gapless at xϾ1.54, explaining qualitatively the dependence of T N /T max on x.

Large quantum fluctuations in the strongly coupled spin-12chains of green dioptaseCu6SiJanson1, Tsirlin2, Schmitt3 et al. 2010Phys. Rev. B3311310View full textAdd to dashboardCite

“…48 However, the pronounced difference in the crystal structures strongly impedes a reliable transfer of the well established magnetic model of the chain compound CuGeO 3 to the Ge-dioptase Cu 6 Ge 6 O 18 . 46 Based on the results for the Si-dioptase, we would expect sizable AFM J c , while J d is either FM or AFM. In the case that the FM and AFM contributions to J d are close to cancel each other, the inter-chain coupling is effectively switched off, and long-range couplings along the spiral chains could alter the physics.…”

“…These compounds were previously considered as coupled frustrated spin chains, because a sizable next-nearest-neighbor coupling along the spiral chains was assumed. 46,47 This assumption is rather empirical and mainly motivated by the chemical similarity to the well-known spin-Peierls compound CuGeO 3 with its frustrated spin chains of edgesharing CuO 4 plaquettes. 48 However, the pronounced difference in the crystal structures strongly impedes a reliable transfer of the well established magnetic model of the chain compound CuGeO 3 to the Ge-dioptase Cu 6 Ge 6 O 18 .…”

Exact dimer phase with anisotropic interaction for one dimensional magnets

“…In experiments, these observations are explained by an isotropic J 1 -J 2 model, which may support dimer phase when α = J 2 /J 1 > 0.2411 [60]. This model was also shown to relevant to other anisotropic quasi-one dimensional magnets such as CuCrO 4 with α = 0.43 [39], BaV 3 O 8 with α ≈ 0.5 [61], Cu 3 (MoO 4 )(OH) 4 with α = 0.45 [42], Cu 6 Ge 6 O 18 • 6H 2 O with α = 0.27 [62], Cu 6 Ge 6 O 18 •H 2 O with α = 0.29 [62] and Li 1.16 Cu 1.84 O 2.01 with α = 0.29 [63]. In some of the experiments, strong anisotropy has been reported; especially, some of these parameters may even be negative valued.…”