We investigate the low-temperature magnetic properties of intermetallic compounds Tb1?xPrx(Fe0.4Co0.6)1.88C0.05 (x=0, 0.8, and 1) by detailed magnetization measurements. Obvious temperature-and field-induced irreversibilities sug-gest the coexistence of multiple magnetic phases. Sharp magnetization jumps across the antiferromagnetic to ferromagnetic transition are observed only in the Pr-containing samples, indicating that the behavior of the avalanche-like growth of fer-romagnetic clusters is mainly related to the light lanthanide Pr ions. In addition, the time relaxation, field sweep rate, and cooling field dependence of magnetization jumps in the sample with x=1 are consistent with those in the martensitic scenario.