Magnetization dynamics in CoFe∕AlO/Permalloy and CoFe∕MgO/Permalloy magnetic tunnel junctions

This paper presents a theoretical study about the effect of nonidealities in the shape of elliptical cross sectional area of magnetic tunnel junctions on the magnetization dynamics driven by spin-polarized currents (no applied field). The set of nonideal shapes has been computed from scanning electron microscopy images directly. The polarization function deduced by Slonczewski in 2005 [Phys. Rev. B 71, 024411 (2005)] has been used for the simulations, considering the polarization factor independent of the bias. Depending on the shape, results of micromagnetic simulations show that the main steps of the magnetization dynamics do not change qualitatively, but in contrast, (a) other modes (defect modes) are excited, (b) a shift in the excited main mode is observed, and (c) the spatial distribution of the main mode changes.