139La NQR study of antiferromagnetic La2NiO4+δ

The magnetic properties in the La 2 NiO 4+δ system have been investigated by 139 La nuclear quadrupole resonance (NQR). The structure or the NQR spectrum at 1.4 K was found to depend sensitively on annealing procedures of the compounds, and therefore on δ. A well-characterized spectrum was obtained for samples oxygenated (δ≧0.066) and deoxygenated (δ∼0.022) with different structures, exhibiting the existence of the internal magnetic fields H mt of ∼17.8 kOe nearly parallel to the basal Ni–O plane and ∼19.3 kOe perpendicular to the plane. The strength of H mt at the La site was significantly large when compared with that of ∼1 kOe in La 2 CuO 4 and could not be explained simply by the dipole field caused by Ni spin moments.