We investigate a variation of magnetic domain pattern in demagnetized perpendicular-easy-axis CoFeB/MgO stacks with a wide-range electric field and discuss the electric-field effect on the exchange stiffness constant AS. We observe a non-linear variation of domain period DP with the applied electric field, in contrast to the effective perpendicular anisotropy field HKeff that is evaluated from a ferromagnetic resonance and shows a linear response. An analysis based on a model describing the relation of DP to AS and HKeff suggests that AS varies non-linearly with the electric field, implying an involved characteristic mechanism of the exchange stiffness in the studied systems. A possible scenario for explaining the non-linear behavior of AS is discussed.
ASJC Scopus subject areas