  The complex dynamic Young's modulus of ceramic Nd2-xCexCuO4 with x = 0, 0.05
and 0.20 has been measured from 1.5 to 100 K at frequencies of 1-10 kHz. In the
undoped sample the modulus starts decreasing below ~20 K, instead of
approaching a constant value as in a normal solid. The modulus minimum has been
interpreted in terms of paraelastic contribution from the relaxation of the
Nd^3+ 4f electrons between the levels of the ground state doublet, which is
split by the interaction with the antiferromagnetically ordered Cu sublattice.
The value of the splitting is found to be 0.34 meV, in excellent agreement with
inelastic neutron scattering, infrared and specific heat experiments. With
doping, the anomaly shifts to lower temperature and decreases in amplitude,
consistently with a reduction of the local field from the Cu sublattice.
