¹³⁹La NQR Study of Antiferromagnetic La₂NiO_4+δ

Abstract

The magnetic properties in the La₂NiO_4+δ system have been investigated by ¹³⁹La 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 La₂CuO₄ and could not be explained simply by the dipole field caused by Ni spin moments.