Coupled antiferromagnetic spin-1/2 chains in green dioptase, Cu6 [Si6O18.6] H2O
Abstract
Gem crystals of natural dioptase with colors ranging from emerald-green to bluish have delighted people since ancient times and still attract attention of mineral collectors around the globe. The crystal structure of green dioptase (space group R 3) consists of corrugated silicate rings Si6O<18 interconnected by Cu2+ ions. Oxygen atoms form axially-elongated octahedral of CuO4(H2O)2. The magnetic ground state of green dioptase remains controversial. We report inelastic neutron scattering measurements of the magnetic excitations of green dioptase Cu6 [ Si6O18.6 ] H2O. The observed spectrum contains two magnetic modes and a prominent spin gap that is consistent with the ordered ground state of Cu moments coupled antiferromagnetically in spiral chains along the c axis and ferromagnetically in ab planes on the hexagonal cell. The data are in excellent agreement with a spin-1/2 Hamiltonian that includes AFM nearest-neighbor intra-chain coupling Jc = 10 . 6 (1) meV, ferromagnetic inter-chain coupling Jab = - 1 . 2 (1) meV and exchange anisotropy ΔJc = 0 . 14 (1) meV. This appears compatible with reduced Nèel temperature, TN = 14 . 5 K <<Jc , and can be explained by a presence of quantum spin fluctuations.
Research at Oak Ridge National Laboratory's Spallation Neutron Source and High Flux Isotope Reactor was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2017
- Bibcode:
- 2017APS..MARC50001P