MAGNETIC PHASE-TRANSITIONS IN THE HUBBARD-MODEL WITH LARGE ON-SITE COULOMB REPULSION

For the (t - J) model temperatures T-K and T-N of the phase transitions in ferromagnetic and antiferromagnetic phases are calculated. It is shown that T-N fails dramatically with deviation from a half-filling, but T-K increases, passing through a maximum. Such a behaviour of T-N with electron concentration corresponds to observations on copper oxide high-T-c materials. For the Hubbard model at strict half-filling, T-N is calculated as a function of the Coulomb repulsion parameter.