Nucleation and evolution of hybrid spin spiral in soft/hard ferromagnetic bilayer

The hybrid exchange spring behavior in a bilayer consisting of an epitaxial film of Fe (500 Å)/Sm2Co7 (350 Å) deposited onto a Cr (200 Å) buffered MgO(110) substrate was investigated using the magneto-optical indicator film technique. Two critical magnitudes of the remagnetizing magnetic field were found that dramatically change the bilayer remanent magnetization. One of them is determined by exchange spring penetration in the interface; another is determined by hybrid spin spiral transformation to domain walls in the hard ferromagnet layer. Unexpected dependence of the direction of average remanent magnetization on the external magnetic field direction and value is revealed.