A new theoretical approach on the spin-crossover materials: Correlated Mean-Field and Effective-Field theories

General formulation for the Mean-Field and Effective-Field theories, with correlations, on the Ising model spin-1/2, were derived to describe the switching properties between the LS and HS states in SCO nanoparticles, with objective of present a new theoretical approach on the spin-crossover materials. These two methods were applied on the Ising spin-1/2 model in a 3D spin crossover nanoparticle. By applying the Mean-Field theory and Effective-Field theory in this way, we have solved a set of coupled equations that correlates the averages of the spins located at the edge ( σ E ), corner ( σ C ), surface ( σ S ) and bulk ( σ B ), present in a lattice of SCO nanoparticles. Besides the magnetizations and thermal evolution of the HS molar fraction, we have obtained some phase diagrams and free energies of the system.