Toward further understanding of the magnetization switching mechanisms, the magnetization reversal study was performed by utilizing the simulation code (OOMMF) developed by NIST.  The magnetization reversal simulation was applied on a nickel microbar.  Saturation magnetization used for modeling was M_s = 4.9·10⁵ A m^-1, with the cell size 10nm x 10nm x 55 nm (film thickness).  The magnetocrystalline anisotropy coefficient, K₁, was set to zero, implying the polycrystalline nature of microbars.  The exchange stiffness parameter A was set to 9·10^-12 J m^-1, while damping coefficient a was set to 0.1.  Each cell used for calculation encompassed a template area of 5x5 pixels. The geometry used for modeling was an actual AFM image of a Ni-microbar, produced by electrodeposition in a void prepared by nanoimprint lithography. The characteristics of a Ni-microbar were: Aspect ratio=5.00, some edge roughness, and oval ends with slight irregularities.

        It was found that the magnetization reversal initiates by vortices formed at the microbar ends, with simultaneous formation of 90º transverse domain walls across the microbar.  The magnetization reversal proceeds by propagation of vortex cores perpendicularly to the direction of applied field (long axis), and gradual reversal in the central area of a microbar.  Notice that edge irregularities serve as pinning sites for magnetization reversal.