The microstructural and magnetic properties of amorphous Co/Ti multilayer films and their variation with temperature are investigated by transmission electron microscopy (TEM) analysis and thermomagnetic measurements. Thermomagnetic curves showed two peaks at about 400 and 520 °C. The evolution of the structure monitored in the hot stage of the TEM was found to be consistent with the magnetic changes. The first peak of the saturation magnetizationMsat 400 °C was associated with the transformation from amorphous ferromagnetism to paramagnetism due to the amorphous Co existing in the film.Msbegan to increase corresponding to the crystallization point of the ferromagnetic Co phase, which decreased with increasing amounts of Co in the film.Msreached its maximum at 520 °C and then decreased because the phase transition occurred at a temperature greater than 520 °C and approached completion at 650 °C. The amorphous phase and crystalline phase formation and phase transition during annealing were observed in Co/Ti multilayer thin films and successfully explained the thermomagnetic properties of the film. ©1997 American Institute of Physics.