Neutron scattering study of the layered Ising magnet CsDy ( MoO 4 ) 2

The quasi-two-dimensional antiferromagnet CsDy ( MoO 4 ) 2 is studied by neutron diffraction and quasielastic neutron scattering. The crystal structure of two low-temperature phases (below 120 K and below 40 K) is determined. An approximate structure of the magnetically ordered phase (T N =1.36 K ) is proposed. In the ordered state the order-parameter critical exponent β=0.17(0.01), the in-plane correlation length exponent ν=0.94(0.07), and the staggered susceptibility critical index γ=1.01(0.04) were determined. Comparing these results to the exact solution for a 2D Ising magnet, we conclude that, although 2D behavior is apparent in CsDy ( MoO 4 ) 2 , there are deviations from the simple 2D Ising model.