Evolution of low-dimensional magnetism in Mg-substituted CoTa₂O₆

Co²⁺ moments in the trirutile compound CoTa₂O₆ form a square-net in two-dimensions. The system exhibits three-dimensional ordering described by a propagation vector of (1/4,1/4,0) below a Neel temperature of T_N=6.2 K wherein moments align (++--) in chains along the (110) and (1-10). Anomalies in the magnetization and specific heat have indicated the presence of correlations above the Neel temperature, whereas no diffuse scattering was observed the elastic neutron scattering signal as would be expected for three-dimensional short-range order. Further, it has been shown that the ordering at 6.4 K is destroyed by even a small amount (x = 0.1) of non-magnetic doping with Mg on the Co site. We therefore have investigated the series Co_1-xMg_xTa₂O6 via inelastic neutron scattering in order to gain insight into the spin correlations both below and above the ordering temperature and their evolution with lattice dilution. We discuss the results in the context of anisotropic exchange interactions and reduced dimensionality of the magnetic lattice.