Powder neutron diffraction and resonant x-ray scattering measurements from a single crystal have been performed to study the low-temperature state of the 2D frustrated, quantum-Heisenberg system ${\mathrm{L}\mathrm{i}}_2{\mathrm{V}\mathrm{O}\mathrm{S}\mathrm{i}\mathrm{O}}_4$. Both techniques indicate a collinear antiferromagnetic ground state, with propagation vector $k=\left(\frac{1}{2}\frac{1}{2}0\right)$, and magnetic moments in the $a\mathrm{\text{−}}b$ plane. Contrary to previous reports, the ordered moment at 1.44 K, $m=0.63\left(3\right){\mu }_B$, is very close to the value expected for the square lattice Heisenberg model ($\simeq 0.6{\mu }_B$). The magnetic order is three dimensional, with antiferromagnetic $a\mathrm{\text{−}}b$ layers stacked ferromagnetically along the $c$ axis. Neither x-ray nor neutron diffraction shows evidence for a structural distortion between 1.6 and 10 K.

• Received 15 December 2003

DOI:https://doi.org/10.1103/PhysRevLett.93.027202