Magnetic structure of doped antiferromagnet

We investigated t-J and t-t'-J model, focusing on their magnetic structures in low but finite doping region. By rewriting hopping term, we obtain new forms of the models which show more explicitely an interaction between carrier hopping and spins. In t-J model, a spiral order appears upon doping and discontinuously changes to ferromagnetic order at a critical doping δc 3(1 + √2)J/8t, although the spiral order is unstable against density fluctuations. With the next-nearest neighbor hopping t' being finite, antiferromagnetic phase occupies finite region in the vicinity of half-filling in the magnetic phase diagram. (orig.)