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The nature of the spin‐cluster (“multi‐magnon”) excitations which have been observed in CoCl2·2H2O at liquid helium temperatures is reviewed. Using the far infrared laser lines of HCN and DCN, the authors measured the spin‐cluster resonance linewidths as a function of sample temperature and found excellent agreement to a simple exponential broadening law with a single characteristic energy independent of cluster size. It seems possible that the optic phonon which intersects the Ising “fan” of excitations is playing the dominant role in the relaxation mechanism giving rise to the T‐dependent energy widths.