Abstract
Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO2, NaYbS2, and NaYbSe2, exhibit no long-range order down to the lowest measured temperatures and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS2 exhibits magnetic order below T N = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called ‘stripe-yz’ type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce–Ce bonds. No structural lattice distortions are revealed below T N, indicating that the triangular lattice of Ce3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS2, based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure.
Highlights
In low-dimensional quantum magnets, competing exchange interactions may lead to a strong frustration accompanied by enhanced quantum fluctuations
This can prevent the systems from long-range order, and the ground state is supposed to be a quantum spin liquid (QSL) [1,2,3,4]
We have presented the results of magnetic structure refinement for the low-temperature AFM state, which was recently revealed in the effective spin-1/2 triangular-lattice antiferromagnet KCeS2
Summary
In low-dimensional quantum magnets, competing exchange interactions may lead to a strong frustration accompanied by enhanced quantum fluctuations This can prevent the systems from long-range order, and the ground state is supposed to be a quantum spin liquid (QSL) [1,2,3,4]. The most promising candidate compounds in this class are honeycomb-lattice iridates (α-Li2IrO3, Na2IrO3, H3LiIr2O6) [7,8,9,10,11] or ruthenates (α-RuCl3) [14,15,16,17,18] and their three-dimensional polymorphs that form hyper-honeycomb (β -Li2IrO3) [12] or stripy-honeycomb (γ-Li2IrO3) [13] structures The difficulty with these model systems is that in real materials, Kitaev interactions coexist with Heisenberg exchange and. We have investigated the magnetic structure of the low-temperature ordered phase in KCeS2 and its low-temperature lattice structure using powder neutron diffraction
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