Inelastic neutron scattering and magnetic susceptibility measurements have been performed on the distorted perovskite NdGaO3. The magnetic susceptibility data show a Curie-Weiss behaviour with an effective magnetic moment close to 3.6 mu B per mole of Nd ions. No long-range magnetic ordering was detected in the temperature range 2-300 K. The inelastic neutron spectra observed at T=12 K exhibit four peaks of magnetic origin between 11 and 7D meV which can be unambiguously assigned to the complete crystalline-electric-field splitting pattern in the ground-state J multiplet 4I9/2 of the Nd3+ ions. We analysed the spectra in terms of geometrical considerations based on the actual C2 site symmetry of Nd3+. The best agreement between the experimental spectra and the calculated level structure was obtained for a model that takes into account the three nearest-neighbouring coordination polyhedra associated with the O2-, Ga3+ and Nd3+ ions as well as J-mixing between all multiplets of the 4I term. We conclude that single-particle crystal-field theory adequately explains the majority of magnetic and crystal-field properties of NdGaO3.

Single-crystal neutron diffraction was employed to study the magnetic transition in the pseudobinary Lavesphase compounds Er 1Ϫx Y x Co 2 (xϭ0, 0.4) under external magnetic fields up to 4 T. The magnetic scattering amplitudes measured for the reflections to which either the localized 4 f Er moment or the itinerant 3d Co moment solely contributes, give direct evidence that the onset of long-range magnetic order for both magnetic sublattices occurs at about the same temperature T C ϳ35.9 and 17.0 K for xϭ0 and 0.4, respectively. The magnetic-susceptibility and specific-heat data, obtained on the same specimens, were also measured. In agreement with the neutron-diffraction data the macroscopic measurements showed no multiple phase transitions as opposed to earlier measurements on powder samples, which are presented and discussed as well.

A model of the crystal field generated by a periodic array of charged tapes is developed to analyse the crystal-field interaction in RBa2Cu3Ox (R = Er, Ho) high-Tc copper oxides observed by the inelastic neutron scattering technique. The explicit calculation of the parameters of the Stevens Hamiltonian describing crystalline electric field effects in solids is performed for a specific charge density distribution uniformly extended in a certain direction of the crystal lattice. The model accounts for the x-dependence of the crystal-field parameters and allows us to determine the hole concentration in the CuO2 planes as a function of oxygen stoichiometry. The model of the periodic array of charged tapes suggests a charge order induced in the CuO2 planes by doping.

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