Magnetic susceptibility, NMR, muon spin relaxation, and inelastic neutron scattering measurements show that kapellasite, Cu3Zn(OH)6Cl2, a geometrically frustrated spin-1/2 kagome antiferromagnet polymorphic with herbertsmithite, is a gapless spin liquid showing unusual dynamic short-range correlations of noncoplanar cuboc2 type which persist down to 20 mK. The Hamiltonian is determined from a fit of a high-temperature series expansion to bulk susceptibility data and possesses competing exchange interactions. The magnetic specific heat calculated from these exchange couplings is in good agreement with experiment. The temperature dependence of the magnetic structure factor and the muon relaxation rate are calculated in a Schwinger-boson approach and compared to experimental results.
While much is becoming known experimentally about the effects of frustration in the classical limit, such as in the 3dimensional pyrochlores 1,2,3 and 2-dimensional (2D) kagome lattice 4,5,6,7,8 , what happens in the S=1/2 quantum limit is little characterized due to the scarcity of model materials. This has led to one of the most enduring problems in condensed matter physics: the search for the 'resonating valence bond' (RVB) state. The state was proposed by Anderson over two decades ago to underpin the transition to BCS superconductivity. 9 The RVB is a quantum state made by the spin pairing of electrons on different sites. Its highly entangled nature makes it an essential reference for the physical sciences, and for the current efforts in the development of states that can be exploited for quantum computing 10 The S=1/2 kagome antiferromagnet (KAFM) is a good candidate for the realization of the RVB state 11,12,13 and much 1
The search for new S = 1/2 kagome antiferromagnets has been an ongoing challenge for the researchers interested in frustrated magnetism. Intrigue has surrounded these materials since the proposal that the high frustration of the kagome antiferromagnet and quantum fluctuations could prevent the formation of conventional Néel order and allow the formation of the resonating valence bond (RVB) state at low temperatures. There remain relatively few examples of S = 1/2 kagome magnets with crystal structures that have 3-fold symmetry, as many feature distortions that lower the crystal symmetry to monoclinic and reduce the degeneracy of the kagome lattice. In this article, we detail the synthesis and preliminary magnetic investigations of a new quantum kagome magnet, haydeeite, α-Cu3Mg(OH)6Cl2. Comparisons with the isomagnetic and isostructural analogue kapellasite, α-Cu3Zn(OH)6Cl2, are discussed.
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