Effects of the removal of Ta capping layer on the magnetization dynamics of Permalloy thin films

We have investigated the spin wave dynamics of Permalloy (Py) thin films with and without a Ta capping layer for varying Py thickness (15 nm, 20 nm and 30 nm) using all optical time-resolved magneto-optical Kerr effect measurements. XPS measurements confirm the oxidation of the originally-prepared samples and also that the removal of the Ta capping layer is achievable by a few sputtering cycles. The magnetic field strength dependencies of the spin wave modes with the variation of the Py film thickness for the samples are studied. We observe that the presence of the Ta capping layer reduces the precessional frequencies of the samples while the samples without a Ta capping layer enhance the role of Py thickness. We also observe that the decay time of spin waves is highly dependent on the top layer of the samples. The decay time increases with increasing Py thicknesses for Ta/Py/Ta samples implying that the enhancement of decay time is caused by the Ta/Py/Ta interfaces. Whereas, for Ta/Py samples the decay time decreases with increasing Py thickness. The results of this work extend the knowledge on the magnetization dynamics of Py thin films giving information on how to resume and even enhance the spin mobility after a deleterious oxidation process. This can open new scenarios on the building process and on the maintenance of fast magnetic switching devices.