Magnetic resonance in oxygen-doped La2NiO_{4 + \delta }

We report an investigation of magnetic resonance by ESR in oxygen-doped La₂NiO emphasizing extensively for the first time the role of oxygen stoichiometry. The work is performed at room temperature and on powders with . At low field an hysteresis is detected between increasing and decreasing fields, it depends upon . The resonance lines have characteristic features of ferromagnetic resonance. The intensity () is used as an experimental parameter for investigating the effect of . It allows to built a diagram closely connected to the phase diagram . It suggests a ferromagnetic coupling depending upon . When the (average) structure is tetragonal the low intensity is due to a magnetic polaron of low resistivity. In ranges where a phase separation is detected, the ferromagnetic coupling has a structural origin (DM or local anisotropy) with apparently a strong influence on the electrical resistivity. Received: 3 November 1997 / Accepted: 23 December 1997