SIMULTANEOUS ORDERING OF HOLES AND SPINS IN LA2NIO4.125

We report a single-crystal neutron diffraction study of the incommensu rate magnetic ordering that occurs in La2NiO4.125 below 110 K. Besides the magnetic first and third harmonic Bragg peaks, we have also obser ved second harmonic peaks associated with charge ordering. The magnitu de of the incommensurate splitting, epsilon, is strongly temperature d ependent. Lock-in behavior indicates that epsilon tends to rational fr actions, while regions of continuous variation suggest a devil's stair case. Analysis of these features indicates that the holes, induced by the excess oxygen, order in domain walls that form antiphase boundarie s between antiferromagnetic domains.