MAGNETIC ORDER IN THE T-J AND T-T'-J MODELS

The magnetic structure of the t-J and t-t'-J models are investigated. Assuming that the ground state has magnetic long-range order, we calcu lated the energy of some magnetically ordered states using a simple tr ansformation of the models and the S-->infinity approximation. The res ult shows that the Neel state is destroyed by doped holes unless the n ext-nearest neighbor hopping t' is finite, and that the ferromagnetic phase appears at moderate doping. Mean field analysis shows that the i ntermediate phase between the Neel and ferromagnetic phase has spiral spin order, although the spiral phase is shown to be unstable against density fluctuations.