ONE-DIMENSIONAL MAGNETISM AND THE PHASE-TRANSITION IN VOMOO4

A crystal of VOMoO4 was grown, which has a structure containing V-O-V- O linear chains along the c-axis. There a vanadium ion carries a spin of 1/2 per ion. The magnetic susceptibility was measured in the region from 2 to 300 K up to 55 kG. The temperature dependence shows a broad maximum around 100 K. This is a characteristic of a 1D antiferromagne t. Fitting to the uniform 1D Heisenberg model is very good in the high er temperature region. This suggests the onset of antiferromagnetic or der around 100 K. At 34 K, however. chi shows a kink followed by a fer romagnetic hump at lower temperature. This suggests some magnetic phas e transition. At 2 K a slight hysteresis was observed in the magnetic field dependence. The above behaviour was interpreted as the process o f transfer from 1D to weak 3D interaction, according to lowering tempe rature. Lattice:parameters increased with decreasing temperature below 100 K, then showed a hump around 30 K. This anomalous behaviour corre sponds to the above magnetic results. It has been concluded that VOMoO 4 is a one-dimensional antiferromagnet. We also suggest the existence of a weak ferromagnetic ordered state such as canted or ferri-magnetis m by the V-O pairs in the lower temperature region.