Magnetic properties of quasi two-dimensional antiferromagnet Rb2MnCl4 with XXZ interaction anisotropy

Two-dimensional Heisenberg antiferromagnet with XXZ spin anisotropy Rb2MnCl4, is studied using the method of double-time-temperature Green's functions (GF) with arbitrary spin S (in particular case S = 5/2) within random-phase approximation (RPA) and Callen approximation (CA). Exchange field and anisotropy field are extracted from experimental data on the magnon frequencies in Rb2MnCl4. They are used to calculate dispersion relation and the sublattice magnetization in the self-consistent way in the whole temperature range. The results obtained using RPA and CA are compared. The existence of a finite temperature transition is investigated, probably describing the low-temperature critical behavior experimentally observed in many layered compounds. The N,el temperature T-N is calculated employing both methods. Calculated transition temperature within RPA agrees rather well with the measured values for the quasi two-dimensional antiferromagnet Rb2MnCl4 in zero magnetic field, while CA overestimates the critical temperature. The dependence of critical temperature on parameter of spin anisotropy eta is also analysed. The good agreement found between our theoretical results and the experimental data relative to the real compound Rb2MnCl4 shows that the inclusion of this type of spin anisotropy with quantum effect properly taken into account, provides a quantitative description and explanation of the experimental data.