Modulation of Magnetization Precession Trajectories by Perpendicular Magnetic Anisotropy in CoFeB Thin Films

Precession trajectories during excitation of magnetization dynamics play an important role in determining spin wave propagation, emission power of spin torque oscillator, and spin current generated by spin pumping. However, comparatively little information has emerged on the effect of perpendicular magnetic anisotropy (PMA) on dynamical magnetization trajectories. The effect of PMA on magnetization dynamics has become particularly important since the discovery of voltage control of magnetic anisotropy in CoFeB/MgO junctions. This motivates us to investigate the effect of PMA on dynamical magnetization trajectories of CoFeB thin films using micromagnetic simulations. The ellipticity of the trajectories is found to increase monotonically with PMA. On the other hand, the area of such elliptical trajectories, which determine the spin current generation, shows a non-monotonous change with respect to PMA. This area can be expected to be maximum for the case where ellipticity is similar to 0.5.