The Effect of Defects on Precessional Dynamics in a Magnetic Field and Resulting Spin Wave Modes in Elliptical Nanomagnets with In-Plane Anisotropy

We have simulated the precessional dynamics of magnetization in elliptical nanomagnets biased with an in-plane magnetic field along the minor axis and perturbed by a small out-of-plane magnetic field. The precessional dynamics gives rise to spin wave modes in the nanomagnets. We first calculate the time-dependent out-of-plane component of the magnetization at a fixed plane of the magnet at various coordinate points and also the spatially averaged magnetization as a function of time. We then find the Fourier transform of the spatially averaged component to find the dominant precessional frequencies (which do not necessarily correspond to the Kittel frequencies) and calculate the power and phase profiles of the spin wave modes at those frequencies. We find that the spin wave modes are significantly affected by the presence of defects in the nanomagnets. We have studied six different types of defects arising from material voids and thickness variations which are realistic defects that arise during fabrication processes. Our results show that the spin wave modes are significantly affected by defects. This has a serious implications for devices that rely on spin wave modes such as oscillators and neuromorphic computers based on phase locked oscillators.