Micromagnetic Simulations of Highly Non-linear Modes in Spin Torque Oscillators: Propagating, Solitonic and Magnetic Dissipative Droplet Modes
Magnetic dynamics can be locally excited in spin valve structures by the current-induced spin transfer torque (STT). Such devices are generally referred to as Spin Torque Oscillators where the high current densities required are, for instance, achieved by patterning a metallic nanocontact on top of the spin valve (NC-SV). The resulting dynamics are analytically described with the Landau-Lifshitz-Gilbert-Slonczewski equation. Unfortunately, its high non-linearity limits the analytical insight that can be gained from it. In this seminar, we will show two cases where numerical simulations are required to accurately represent the system under study.
In particular, we refer to NC-SVs where the active magnetic material exhibits in-plane anisotropy or perpendicular magnetic anisotropy (PMA). In the former, the simultaneous excitation of a propagating spin wave mode and a localized bullet mode is obtained in agreement with recent experimental results. In the latter, we study the nucleation of magnetic dissipative droplets as a function of the sample’s physical confinement i.e. from an extended thin film down to the nanowire limit. These results underline the importance of micromagnetic simulations as a tool for understanding and prediction of the highly non-linear dynamics excited in STT-driven magnetic systems.