Magnetic ordering of the quasi-two-dimensional system VOCl

Abstract

The susceptibility of single crystals of VOCl is isotropic above TN=80.5K and well described by a quadratic two-dimensional (2D) Heisenberg system with a strong antiferromagnetic intra-layer coupling (J/k=-34.5K). Neutron diffraction revealed a collinear antiferromagnetic order with a wavevector k=(1/2 1/2 1/2) 1/2) and the moments along the a axis. Two structures, corresponding to both a ferromagnetic and an antiferromagnetic coupling between the two magnetic Bravais lattices, coexist as a result of the particular value of the wavevector. The order parameter follows a power law at the magnetic transition, with a critical exponent beta =0.143, in agreement with the 2D character and anisotropy of Ising type.