A series of RExTMbalBy (3≤x≤5.5, 15≤y≤25 at%) nanocomposite magnets were prepared using the classical method of alloy rapid quenching and subsequent devitrification. Appropriate elemental additions and substitutions allowed the technical magnetic properties to be optimized. The analysis of the both hysteresis cycles and static susceptibility measurements in the range 20K-300K reveals that magnetization reversal in these materials can be interpreted schematically as a two-step process : the initial magnetization reversal is dominated by reversible processes while irreversible processes, which characterize the coercivity mechanism, occur at larger field values. To complement this study, X-Ray Magnetic Circular Dichroism (XMCD) spectroscopy was applied as an element-selective probe of magnetization reversal in nanocomposite samples. This allowed the hysteresis cycles of both hard and soft phases to be separated from the total cycle. Magnetization processes in these bulk heterogeneous systems are discussed in the light of information brought by the complementary applied experimental techniques.