Using φ field theory and Monte Carlo (MC) simulation we investigate the finite-size effects of the magnetization M for the three-dimensional Ising model in a finite cubic geometry with periodic boundary conditions. The field theory with infinite cutoff gives a scaling form of the equation of state h/Mδ = f(hLβδ/v,t/h1/βδ) where t = (T - TC)/Tc is the reduced temperature, h is the external field and L is the size of system. Below Tc and at Tc the theory predicts a nonmonotonic dependence of f(x,y) with respect to x ≡ hLβδ/v at fixed y ≡...
