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When CuO is cooled below its N\'eel temperature (T₍₂=213 K) the onset of long-range magnetic order effectively increases the unit-cell dimensions and additional peaks, corresponding to zone-folded phonons, appear in the Raman spectrum. The zone-folding mechanism in CuO is unusual in that one of the folded phonons hardens significantly in frequency as the sample is further cooled below T₍₂. It is shown that this dependence on temperature is determined by the sublattice magnetization and that the unusually large shift in frequency is caused by a strong spin-phonon interaction in cupric oxide.
Chen et al. (Wed,) studied this question.