Limited influence of diluted ferromagnetic dimers on Curie temperature in complex magnetic systems

In this work we investigate Ising and classical Heisenberg models for two and three dimensional lattices in presence of diluted ferromagnetic dimers. For such models the Curie temperature as a function of ratio of intra-dimer exchange coupling constant I_A and other inter-site coupling constants I_B is calculated. In case dimer is treated exactly and environment within the mean-field approach it was found that even for I_A/I_B\to\infty T_C remains finite. Similar analysis is proposed for rhombohedral phase of intermetallic compound Gd2Fe17 where so-called Fe1-Fe1 "dumbbell" forms the diluted ferromagnetic dimer. It was shown that for such complex magnetic systems T_C is determined by all variety of exchange interactions and for the interval 0 < I_A/I_B < \infty T_C changes are not more than +/-10%.