Loss of magnetic memory in SMMs, also known as magnetic reversal or magnetic relaxation, occurs through different processes dictated by the spin dynamics. Single-phonon interactions lead to magnetic relaxation via the Orbach mechanism, for which the characteristic time has an exponential temperature dependence 𝜏 = 𝜏 # exp(𝑈 )** 𝑘 , 𝑇 ⁄ ) with a characteristic phonon timescale 𝜏 # and an energy barrier 𝑈 )** , and in the best-performing SMMs this is driven by high-energy optic phonons. At lower temperatures the populations of high-energy phonons are very low and the Orbach mechanism is suppressed. In this regime, the spin dynamics are instead dominated by two-phonon Raman mechanisms driven by low-energy (pseudo-)acoustic phonons, showing a power-law temperature dependence of 𝜏 in the range of T -1 to T -7 . Other mechanisms pertinent to the spin dynamics of SMMs, such as the Direct and Quantum