The simulation of magnetic properties in extended quantum spin networks can be done in good conditions with Ising models within Monte Carlo–Metropolis algorithms, as our systematic studies, employing original computer codes, proved. The present analysis provides interesting insights into the exchange interactions governing the magnetic behavior of the Gd 3 Fe 5 O 12 system, taken as a prototype for ferrites with garnet structure. Effective exchange interaction parameters are estimated by fitting the computed with experimental compensation temperature and temperature dependence of the magnetization.