CRYSTAL-FIELD EXCITATIONS IN ND2-XCEXCUO4

We have measured the complete crystalline electric field (CEF) spectrum of Nd 3+ in superconducting Nd 1.85 Ce 0.15 CuO 4 and in the non-superconducting parent compound, Nd 2 CuO 4 , by neutron inelastic scattering. The best description of the ground state excitations for both compounds is achieved by the addition of a molecular field parameter to the CEF Hamiltonian that takes account of exchange interactions from Nd or Cu spin ordering. This model predicts a small splitting of each of the five crystal field doublets, and the Schottky anomaly associated with the splitting of the ground state is consistent with earlier observations of peaks in the specific heat at low temperatures. The agreement between existing specific heat data and the Schottky anomaly calculated with the assumption of a temperature independent molecular field splitting is very good for Nd 1.85 Ce 0.15 CuO 4 , but for Nd 2 CuO 4 there are differences which may be due to magnetic ordering of the Nd ions and to the change in the molecular field splitting with temperature.