where r is the distance between spins, and d is the dimension of the system, and ϑ ϑ is an exponent, whose value depends on whether the system is in the disordered phase (i.e. above the critical point), or in the ordered phase (i.e. below the critical point). At high temperatures, the correlation decays to zero exponentially with the distance between the spins. The same exponential decay as a function of radial distance is also observed below T c , but with the limit at large distances being the mean magnetization ⟨ ⟨ M 2 ⟩ ⟩ . Precisely at the critical point, an algebraic behavior is seen