Collinear order in the frustrated three-dimensionalspin−12antiferromagnetLi2CuW2O8

Abstract

Magnetic frustration in three dimensions (3D) manifests itself in the spin-1 2 insulator Li2CuW2O8. Density-functional band-structure calculations reveal a peculiar spin lattice built of triangular planes with frustrated interplane couplings. The saturation field of 29 T contrasts with the susceptibility maximum at 8.5 K and a relatively low Néel temperature TN 3.9 K. Magnetic order below TN is collinear with the propagation vector (0, 1 2 , 0) and an ordered moment of 0.65(4) µB according to neutron diffraction data. This reduced ordered moment together with the low maximum of the magnetic specific heat (C max /R 0.35) pinpoint strong magnetic frustration in 3D. Collinear magnetic order suggests that quantum fluctuations play crucial role in this system, where a noncollinear spiral state would be stabilized classically. Introduction. Magnetic frustration, the competition of exchange couplings between localized spins, has broad implications for ground states, excitation spectra, and low-temperature properties. Prominent manifestations of the frustration include peculiar behaviors of spin ice [1], the formation of quantum spin liquids [2], and non-collinear magnetic structures that give rise to spin chirality and strong magnetoelectric coupling [3]. The properties of frustrated magnets change drastically depending on the dimensionality of the spin lattice. Rigorous mapping between theory and experiment requires that both magnetic models and real materials are relatively simple. In this context, the case of isotropic (Heisenberg) exchange on a three-dimensional (3D) lattice of quantum spin-

Frustrated three-dimensional antiferromagnetLi2CuW2O8:Li7Ranjith1, Majumder2, Baenitz3 et al. 2015Phys. Rev. BSelf Cite19691View full textAdd to dashboardCite

“…∆ν is increasing with decreasing temperature and then shows a broad maximum at around 10 K similar to the χ(T ) data. 13 For a comparison, in the same Fig. 4, χ(T ) is also plotted in the right y-axis.…”

“…Compared to the previous study where only bulk measurements were performed, 13 we use NMR, which is a powerful local tool for studying magnetic interactions and magnetic order in frustrated spin systems. The reduction in the ordered magnetic moment (0.65 µ B ) below its classical value of 1 µ B has been ascribed to strong quantum fluctuations, but alternatively it could be understood as a coexistence of ordered and disordered phases below T N .…”

“…The interaction topology in the ab plane resembles a triangular lattice, whereas interplane couplings are oblique and likewise frustrated. 13 There is one Cu site, two equivalent W sites, and two equivalent Li sites in the unit cell. The CuO 6 octahedra that can also be viewed as CuO 4 planar units are connected through WO 6 octahedra.…”

“…Figure 1 shows the triangular layer formed by Cu 2+ ions and the collinear arrangement of spins inferred from the neutron diffraction experiments. 13 The Li atom is coupled to two neighbouring Cu 2+ spins (either up − up or down − down) of the same plane.…”

“…Indeed, we found moderate 1D anisotropy of the 3D spin lattice in Li 2 CuW 2 O 8 with the leading interaction running along the b-direction. 13 However, the purely 1D model is by far insufficient to describe the physics of the compound even in the T ∼ J temperature range.…”