EVIDENCE FOR A STRONG SPIN-PHONON INTERACTION IN CUPRIC OXIDE

When CuO is cooled below its Neel temperature (T-N2=213 K) the onset o f long-range magnetic order effectively increases the unit-cell dimens ions and additional peaks, corresponding to zone-folded phonons, appea r in the Raman spectrum. The zone-folding mechanism in CuO is unusual in that one of the folded phonons hardens significantly in frequency a s the sample is further cooled below T-N2. It is shown that this depen dence on temperature is determined by the sublattice magnetization and that the unusually large shift in frequency is caused by a strong spi n-phonon interaction in cupric oxide.