Magnetic order and lattice anomalies in the J1-J2 model system VOMoO4

High-resolution x-ray and neutron powder-diffraction measurements were performed on polycrystalline VOMoO4. Below ≅40 K the system orders in a simple Neel antiferromagnetic state (propagation vector k-vector=0), indicating a dominant role of the nearest-neighbor interactions. The order is three dimensional but the reduced saturated magnetic moment m of 0.41 (1) μB/V4+ at 2 K indicates strongly two-dimensional character and enhanced quantum fluctuations. On cooling, there is no evidence of a reduction of the crystal symmetry. However, neutron diffraction indicates an anomalous evolution of the lattice parameters, which can be related to the onset of magnetic correlations