The magnetic properties of one-dimensional spin-1 ferromagnetic Heisenberg model in a magnetic field within Callen approximation

► CA is applied to investigate the properties of ferromagnetism and power laws. ► CA provides a simple way to obtain the exponents of power laws. ► The results obtained by applying CA are better than that obtained by applying RPA. ► CA is an improved approximation over the RPA in the case of S=1.