This study investigates magnetic properties of the microcrystalline Sm1 –xZrxFe11Ti (x = 0, 0.1, 0.2) alloys with ThMn12-type structure. The results demonstrate the presence of irreversible magnetization jumps on major hysteresis loops at low temperatures (2–4 K). These jumps occur randomly in terms of the strength of the magnetic field in which they occur and their amplitude and are independent of the chemical composition. There exists a distinct annealing temperature for each alloy, beyond which magnetization jumps are absent in annealed alloys at low temperatures. The magnetic viscosity of Sm0.9Zr0.1Fe11Ti alloy annealed at 700°C was investigated at temperatures of 2–4 K. The results indicate a discontinuity in the magnetic viscosity coefficient in the field of magnetization jump. This phenomenon can be explained by the thermal processes that occur upon the remagnetization of the alloy through the magnetization jump.