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The two phonon Raman process of spin–lattice relaxation is investigated in spin systems having electronic properties appropriate to both optical and acoustic branches of phonon spectrum. Apart from exponential temperature dependence of relaxation times for resonance processes, T⁻³‐, T⁻⁴‐, T⁻⁵, and T⁻⁶‐processes are found for both branches under several conditions. However, when the Debye energy is very high, the T⁻²‐dependence dominates with corrections of T⁻³ and T⁻⁴. The level structure of the spin system is found to be important for the temperature dependence of relaxation times.