Crystal-field and magnetic properties of the distorted perovskite NdGaO₃

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 ⁴I_9/2 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 O^2-, 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.