In this work, we report on the theoretical calculations of the magnetic properties of Fe \( _{100-x} \) (Ga, Ge) \( _x \) compounds ( \( 3.125\le x \le 25 \) at.%). The temperature dependence of the magnetization in the Fe \( _{100-x} \) (Ga,Ge) \( _x \) was found using the Monte Carlo simulation method. The Curie temperatures were found by the Monte Carlo simulation and from mean field theory. We used the magnetic exchange parameters from first-principles calculations to obtain the magnetic phase diagram by means of Monte Carlo simulations using the classical Heisenberg model. We calculated the exchange coupling constants using the SPR-KKR package. The study of the parameters of the magnetic exchange interaction shows that the largest contribution to the total energy of the exchange interaction is associated with the interaction between the pair of nearest neighboring Fe-Fe atoms. The magnetic interactions between Fe-Fe atoms are predominantly FM and sharply decrease with increasing distance between atoms. For D0 \( _3 \) and A2 structures, with an increase in the concentration of Ga(Ge), the phase transition temperature first increases and then decreases. In all cases, the behavior of the ferromagnet–paramagnet phase transition was observed.
