Anisotropic Heisenberg Model on Core-Shell Structured Nanotube Geometry

The effect of the anisotropy in the exchange interaction on the critical temperature and the order parameter of the anisotropic Heisenberg model on a core-shell structured nanotube geometry has been investigated. As a formulation, effective field theory with the differential operator technique and decoupling approximation within the 4-spin cluster (EFT-4) has been used. The variation of the critical temperature with the anisotropy in the exchange interaction has been obtained. Besides, suitability of the effective field theory in small clusters as a formulation for the Heisenberg nanotube has been discussed and it is concluded that minimum size of the cluster is 4-spin cluster, which can give the correct critical description of the system.