MAGNETIZATION AND SUSCEPTIBILITY OF THE 2-SPIN HEISENBERG-MODEL

To take the intra-site spin magnitude fluctuation into account, the us ual one-spin per site Heisenberg Hamiltonian is extended to two intera cting spins per site. We have studied the magnetization and susceptibi lity of the model Hamiltonian as function of temperature and coupling constants using the double-time Green's function method. In contrast t o the one-spin per site Heisenberg Hamiltonian where the Curie constan t depends only on the resultant saturated magnetic moment, our results show that Curie constant of the two-spin per site Heisenberg model de pends rather on the individual moments. Thus, the Curie constant can h ave finite value even when the resultant saturated magnetic moment van ishes. The possible physical implication of our result is also discuss ed. (C) 1997 Elsevier Science Ltd.