Abstract :
The double-time temperature-dependent Green’s function method is used to determine the Néel temperature of a Heisenberg antiferromagnet with easy axis X X Z anisotropy on a D -dimensional bcc lattice. Exact equations within the random phase approximation (RPA) and Callen approximation (CA) in terms of generalized hypergeometric functions valid for arbitrary D , S , and η ≥ 1 are given. Analytical and numerical results presented here strongly suggest that, for D ≥ 2 , the CA gives a higher critical temperature. It is also shown that the RPA set of self-consistent equations yields a Néel temperature closer to the experimental value for compound (CH3NH3)2MnCl4.
