Abstract: Provided is a ferromagnetic free layer, comprising Fe, Co, B and an additive metal, and based on a total atomic number of the ferromagnetic free layer, a content of Co is more than 0 at % and less than 30 at %, a content of B is more than 10 at % and less than or equal to 35 at %, and a content of the additive metal is more than or equal to 2 at % and less than 10 at %; the additive metal comprises Mo, Re or a combination thereof, and a thickness of the ferromagnetic free layer is more than or equal to 1.5 nm and less than 2.5 nm. The ferromagnetic free layer can be applied to a MTJ structure as a single layer, and has sufficient thermal stability for maintaining good magnetic properties after thermal treatment, which makes sure that the MTJ structure can exert normal recording function.