By using the variational principle for the Gibbs free energy, based on the Bogoliubov inequality, the magnetic properties of disordered systems with competing interactions are studied. In our model, we implement periodic boundary conditions stressing on how the number of first nearest neighbors can modify the magnetism. Concerning the competing interactions, we have considered those values corresponding to the ternary system FeMnAl. This system exhibits magnetic phases, like the spin-glass behavior, arising from atomic disorder, bond competition and the dilutor effect of aluminum atoms. In this work we compute the magnetization per site and the magnetic susceptibility, as a function of temperature, for different values of the coordination number. Results reveal an increase of the Curie temperature with the number of first nearest neighbors, as well as the existence of a minimum critical coordination number below which the system becomes paramagnetic.