Cellular Automata Simulation of Two-Layer Ising and Potts Models
Mehrdad Ghaemi · InTech eBooks · 2011
One of the most interesting phenomena in the physics of the solid state is ferromagnetism. Ferromagnetism and antiferromagnetism are based on variations of the exchange interaction, which is a consequence of the Pauli principle and the Coulomb interaction. In the simplest case of the exchange interaction of two electrons, two atoms or two molecules with the spins 1 σ and 2 σ , the interaction has the form 1 2 E Jσ σ = − , where J is a coupling constant which depends on the distance between the spins. When the coupling constant is positive, then a parallel spin orientation is favored. This leads in a solid to ferromagnetism. This happens, however, only when the temperature is lower than a characteristic temperature known as the Curie temperature. Above the Curie temperature the spins are oriented at random, producing no net magnetic field (Fig. 1). As the Curie temperature is approached from both sides the specific heat of the metal approaches infinity.