RAMAN-SCATTERING FROM SINGLE-CRYSTALS OF CUPRIC OXIDE

Raman scattering experiments have been carried out on single crystals of cupric oxide (CuO) in the temperature range from 15 K to 300 K. The symmetry of the three first order Raman active phonons has been determined. A broad peak occurs at approximately 1100 cm-1 and is assigned to multiphonon scattering on the basis of the observed temperature dependence. Another peak appears in the Raman spectrum as the temperature of the sample is lowered below the Néel temperature. The frequency, intensity and linewidth of this peak have been studied as a function of temperature. The frequency of this peak cannot be reconciled with the known spin wave spectrum of CuO and thus, on the basis of the measured temperature dependence, it has been assigned to scattering from a magnetic exciton. The Raman spectrum also contains a background continuum which is weakly peaked at about 2000 cm-1 and the possible origin of this scattering is discussed. The observed optical and magnetic properties of CuO are compared, where possible, to results that have been obtained for the high-Tc cuprates. © 1990.