Magnetic specific heat of Rb₂Co_cMg_1-cF₄: effect of dilution on a two-dimensional Ising-like antiferromagnet

Specific heat of two-dimensional Ising-like antiferromagnets Rb₂Co_cMg_1-cF₄ was measured. The dependence of Neel temperature, T_N, on the concentration of nonmagnetic Mg atoms was obtained by measuring the peak positions of the magnetic specific heat and also of the magnetic diffuse-scattering intensities of neutrons. The results are in fairly good agreement with the prediction from the concentration expansion method over a full range of c. The asymptotic behaviour of the specific heat in the vicinity of T_N is also discussed.