Comparison of time-resolved micromagnetic dynamics experiments on nickel(80)-iron(20) and Landau-Lifshitz-Gilbert micromagnetic simulation.

摘要

Magnetization dynamics in lithographically patterned thin-film permalloy (Ni₈₀Fe₂₀) microstructures are studied using time resolved scanning Kerr microscopy (TR-SKEM). This is a technique combining ultrafast lasers with scanning probe microscopes to observe repetitive non-equilibrium dynamic magnetization states. These observations are compared to a finite element micromagnetic simulation based on the Landau-Lifshitz-Gilbert (LLG) equation. This is a stringent test for the LLG equation, as it will show how well it can reproduce experimental micromagnetics.; Micromagnetic dynamic experiments tested fall into two classes ferromagnetic resonance and magnetization reversal. Ferromagnetic resonance is a low amplitude excitation where the magnetic spins are saturated in one direction and then caused to oscillate at their resonance frequency by a transient magnetic field perpendicular to their saturation direction. Magnetization reversal is a large amplitude excitation where the spin direction in the ferromagnet changes by 180°. The same simulation with the parameters measured with our system (4πM_s = 10.8 kOe and α = 0.008) is quite successful in reproducing experimental behaviour.; Convergence between experimental and numerical micromagnetics is seen in many problems. One large cause of discrepancy, the non-repeatability of dynamics due to Brownian motion of magnetization vectors is studied with simulation. These simulations can be used as a guide to understand the magnetization dynamics experiments in cases where the dynamics are not repetitive.