Tunable non-Gilbert-type damping in Ni80Fe20 films sputtered on the rippled Al2O3 substrates

Splitting phenomenon of ferromagnetic resonance spectra in NiFe films deposited on periodically rippled sapphire substrates

“…The periodically rippled sapphire substrates with a lateral size of 10 mm × 10 mm, mean ripple wavelengths of approximately 100 nm, 140 nm and 200 nm, and corresponding heights of approximately 16 nm, 11 nm and 25 nm were prepared by thermal annealing method [28,29]. These substrates are named as 'Ripple1', 'Ripple2' and 'Ripple3' according to the mean wavelength from small to large since that the modulation of ripple wavelength is more evident than that of height of ripple for these three substrates (see the atomic-force microscopy (AFM) images in figure 1).…”

“…In our prior work [28,29], we prepared periodically rippled Ni 80 Fe 20 (NiFe) films by depositing films on rippled sapphire substrates with different periods where the rippled sapphire substrates were obtained by thermal annealing method. These films were of varying in-plane uniaxial magnetic anisotropy (UMA) and their easy axis of anisotropy is parallel to the ripple direction.…”

“…However, differing from the FMR response of a plane substrate, taken as a reference, with a single peak, the splitting phenomenon of FMR spectra for these periodically rippled films was observed in both the frequency-swept and field-swept FMR experiments. Moreover, the splitting phenomenon was found to be related to the angle between the direction of the ripple and the applied magnetic field [29]. However, the measured FMR response experimentally was only a few one-dimensional (1D) FMR spectra and there was no use of simulation methods, which limits the deeper understanding of this phenomenon.…”

“…The FMR response 2D f (H ext ) color plots are used to achieve a better visualization of 'splitting phenomenon'. The atomic-force microscopy (AFM) images of the three periodically rippled sapphire substrates [28,29]. The x axis is defined by the direction perpendicular to the ripple and y axis is defined by the ripple direction.…”

“…The z axis is along [10-10] of Al 2 O 3 . Adapted from [29], Copyright (2022), with permission from Elsevier.…”