Antiferromagnetism in the Heisenberg Hamiltonian

The shortcomings of the classical theories of antiferromagnetism are reviewed. On the basis of known exact results of several antiferromagnetic models, it is argued that the spin correlation functions may have oscillating behaviour anticipated from the classical Neel states even though the exact ground state is quite different from Neel state. It is also found that as the spin becomes large, the classical results become more and more applicable as seen in Fisher’s model and verified experimentally. A few remarks on the broken symmetry are made. The existence of an anisotropic antiferromagnetic model with Neel states as ground state is pointed out