Measurement of magnetostatic mode excitation and relaxation in permalloy films using scanning Kerr imaging

Abstract

This work presents experimental results of magnetostatic mode excitation using scanning Kerr microscopy under continuous sinusoidal excitation in the microwave frequency range. This technique was applied to $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick permalloy coupons excited in two different ways. In the first experiment, the uniform (Kittel) mode was excited at frequencies in $2.24--8.00\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. The resonant condition was effectively described with the conventional Kittel mode equation. The LLG damping parameter $\ensuremath{\alpha}$ increased significantly with decreasing bias field. It was confirmed that this increase was caused by multidomain structure and ripple domains formed under weak bias fields, as suggested by other studies. In the second experiment, propagating magnetostatic mode surface waves were excited. They showed an exponential amplitude decay and a linear phase variation with distance from the drive field source, consistent with a decaying plane wave. The Damon-Eshbach (DE) model was extended to include a finite energy damping and used to analyze the results. It was found that the wave number and the decay constant were reasonably well described by the extended DE model. In contrast to the first experiment, no significant variation of $\ensuremath{\alpha}$ with frequency or bias field was seen in this second experiment, where spatial inhomogeneities in the magnetization are less significant.