Study of interface induced anisotropic exchange coupling in amorphous FeCoB/MgO bilayer

Abstract

In this work, we present a detailed magneto-optical Kerr effect (MOKE) study of amorphous FeCoB (FCB)/MgO bilayer grown on Si (100) substrate. Two regions with different boron density has been identified in single FCB layer in the as-deposited bilayer due to boron diffusion from FCB to MgO layer at the interface: (i) a boron-deficient layer near FCB/MgO interface (FCBi) and (ii) bulk FeCoB layer (FCBb) located farther away from FCB/MgO interface and having comparatively high boron concentration. As a result, a stress-induced uniaxial magnetic anisotropy is observed in the boron deficient FCBi layer, which is found to be superimposed with the magnetization of FCBb layer. Depending on the angle between the applied magnetic field and the uniaxial easy axis of the FCBi layer, magnetization reversal with single step or double step are observed. Role of interlayer exchange coupling between FCBi and FCBb layer is determined by separating out their magnetic contributions by fitting hysteresis loops with a mathematical function. The disappearance of double step behavior after in-situ annealing up to 473 K, suggests that the observed magnetic anisotropy mainly originates from the strain in the film.