Collinear order in the frustrated three-dimensional spin-1/2 antiferromagnet Li₂CuW₂O₈

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 T_N similar or equal to 3.9 K. Magnetic order below T_N is collinear with the propagation vector (0, 1/2,0) and an ordered moment of 0.65(4) µ_B according to neutron diffraction data. This reduced ordered moment together with the low maximum of the magnetic specific heat (C^max/R similar or equal to 0.35) pinpoint strong magnetic frustration in 3D. Collinear magnetic order suggests that quantum fluctuations play a crucial role in this system, where a noncollinear spiral state would be stabilized classically.