THE FERROMAGNET-ANTIFERROMAGNET TRANSITION IN FRUSTRATED QUANTUM SPINMODELS

The character of the transition between the ferromagnetic and the anti ferromagnetic ground states in systems of strongly correlated electron s is studied in a framework of frustrated quantum spin models. A pertu rbation theory in a small parameter characterizing the transition and new variational approach have been used. It is shown that the transiti on from the state with maximal spin to the state with S=0 occurs by pa ssing the states with intermediate spins though the character of the t ransition depends on parameters of models.