Crystal fields in Nd2−xSrxNiO4+y

We have measured, by means of neutron inelastic scattering, the ground state crystalline electric field excitations in the system Nd2−xSrxNiO4+y for x = 0 and 0.4. The excitations occur at 8.0, 23, 38 and 49 meV in the undoped compound, and at similar energies for the Sr-doped material. A notable feature of the spectra is the large intrinsic width of the peaks, which could be due to disorder or to exchange interactions with the Ni-O planes.