The method of exchange perturbation theory as applied to magnetic ordering in high-Tc materials

We unify the method of exchange perturbation theory for multicenter systems. For the case of exchange degeneracy in the total spin of the system we give a secular equation that is more compact and convenient for calculations than those obtained earlier. On the basis of this formalism we develop an algorithm for calculating the Heisenberg parameter for magnetic materials. Finally, we calculate the characteristics of antiferromagnetic transitions for the high-Tc materials La2-xMeCuO4 and YBa2Cu3O6.