Theoretical study of anisotropic layered antiferromagnets

We develop the field theory of antiferromagnets to layered structures on BCT crystal lattices with nearest-neibour and next-nearest-neighbour ferro- and/or antiferromagnetic interactions. For this aim the field theoretical counterpart of a lattice Heisenberg model is derived by standard theoretical methods: Hubbard-Stratonovich transformation and a generalized mean-field approach. We shown that the inter-layer interactions are a pure thermal fluctuation effect whereas the ground state is characterized by a perfect in-layer antiferromagnetic order and a lack of inter-layer coupling. This is a demonstration of 2D-3D dimensional crossover which is supposed to occur in real antiferromagnets, for example, in the spin-dimer antiferromagnet BaCuSi2O6.