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

Abstract

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 Néel 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 η 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.