Universal temperature dependence of the magnetic excitations

Saturation of the magnetic order parameter for T→0 can be described to a good approximation by the empirical power function 1-ms(T)=cTεv. Normally, this function holds up to ∼0.85Tc where the analytical change (crossover) to the critical power function with exponent β occurs. The two exponents ε and β are universal, i.e. they are independent of spin structure and lattice symmetry. This implies that the thermodynamics of the order parameter is not related to the shape of the magnetic excitation spectrum. We show that this is because the magnetic excitations also decrease with the same Tε function