On the Nature of the Spin Frustration in the CuO₂ Ribbon Chains of LiCuVO₄: Crystal Structure Determination at 1.6 K, Magnetic Susceptibility Analysis, and Density Functional Evaluation of the Spin Exchange Constants

Abstract

The spin-1/2 Cu 2+ ions of LiCuVO 4 form one-dimensional chains along the bdirection, and the spin frustration in LiCuVO 4 is described in terms of the nearestneighbor ferromagnetic exchange J 1 and the next-nearest-neighbor antiferromagnetic exchange J 2 in these chains. Recently, it has become controversial whether or not J 1 is stronger in magnitude than J 2 . To resolve this controversy, we determined the crystal structure of LiCuVO 4 at 1.6 K by neutron diffraction, analyzed the magnetic susceptibility of LiCuVO 4 to deduce the Curie-Weiss temperature  and the J 2 /J 1 ratio, and finally extracted the spin exchange constants of LiCuVO 4 on the basis of density functional calculations. Our work shows unambiguously that the Curie-Weiss temperature  of LiCuVO 4 is negative in the range of 20 K, so that J 2 is substantially stronger in magnitude than J 1 .

The strength of frustration and quantum fluctuations in LiVCuO 4

“…3. Notice the strong deviation of the weak-coupling proposal by Koo et al [15]. Then, a dominant FM interchain coupling as proposed in Refs.…”

“…In addition, the striking discrepancy of a very recent parameter set obtained in Ref. [15] with available experimental data, including also Refs. [5,6] will be shown, too.…”

“…[3,5,[14][15][16] (a) Corresponding author, E-mail: s.l.drechsler@ifw-dresden.de Keeping in mind the weak interchain coupling, the singlechain can be viewed also as two interacting and interpen- Magnetic dynamical structure factor S(k, ω) from exact diagonalizations for periodic chains and L = 28 sites for the parameter sets proposed in Ref. [5] (a), our recent findings [16] (b) and that by Koo et al [15] for U = 5 eV (see Tab. 1) (c). Right: experimental asymmetric dispersion along the chain direction in between Ω+ and Ω− (see Fig.…”

“…Finally, the reasons of the incorrect parameter assignment given in Refs. [3,5,15] are explained Table 1: Exchange integrals (in meV) as extracted from INS data using bare spin wave theory (BSWT), ad hoc renormalized spin wave theory (RSWT) [3] or RPA [5] as compared with parameters derived from mapping of microscopic models (see sect. 3).…”

“…However, following our recent work [16] we will show here in more detail that the in-chain exchange integrals J 1 and J 2 , respectively, are significantly different from those suggested in Refs. [3,5,6,15]. Furthermore it has been claimed that the FM coupling J 1 can be fixed at its bare value J ≈3.4 meV [5].…”