a b s t r a c t We present experimental evidences for magnetization modification by superconductivity in a series of Nb/Ni 80 Fe 20 /Nb trilayers. By monitoring the magnetization in a zero field as a function of temperature, we observed an irreversibility in magnetization between the cooling and warming branches just above the superconducting transition temperature T c . These results suggest that the magnetization of the ferromagnetic Ni 80 Fe 20 layer is reduced by the mutual interactions between the ferromagnet and superconductor. Moreover, this effect diminishes with increasing thickness of the Ni 80 Fe 20 layer, which indicates that the interaction between the superconducting and magnetic layers occurs mainly at the vicinity of the interfaces.