Statistics of the Two-Dimensional Ferromagnet. Part I
In an effort to make statistical methods available for the treatment of cooperational phenomena, the Ising model of ferromagnetism is treated by rigorous Boltzmann statistics. A method is developed which yields the partition function as the largest eigenvalue of some finite matrix, as long as the manifold is only one dimensionally infinite. The method is carried out fully for the linear chain of spins which has no ferromagnetic properties. Then a sequence of finite matrices is found whose largest eigenvalue approaches the partition function of the two-dimensional square net as the matrix order gets large. It is shown that these matrices possess a symmetry property which permits location of the Curie temperature if it exists and is unique. It lies at J/kTc=0.8814 if we denote by J the coupling energy between neighboring spins. The symmetry relation also excludes certain forms of singularities at Tc, as, e.g., a jump in the specific heat. However, the information thus gathered by rigorous analytic methods remains incomplete.