Raman study of intermultiplet crystal-field excitations inNd2CuO4

We have observed Raman active ${\mathrm{Nd}}^{3+}$ crystal-field (CF) excitations as a function of temperature in reduced single crystals of ${\mathrm{Nd}}_2$ ${\mathrm{CuO}}_4$. The lines detected correspond to 13 different transitions involving crystal-field split levels of the (J=9/2) ground state as well as the higher excited multiplets with J=11/2, 13/2, and 15/2. Eight of these excitations have been measured out of resonance, thus allowing their symmetry to be determined. Using these levels, we have calculated an unequivocal set of CF parameters, thus solving an outstanding controversy between different neutron measurements. We conjecture that changes in the spectra measured on the reduced sample compared to the as-grown one result from the removal of apical oxygen.