Ferromagnetic resonance study of thickness-dependent magnetization precession in Ni80Fe20 films

The ferromagnetic resonance (FMR) behaviors for Ni80Fe20 Permalloy films with a wide thickness range from 30 to 360 nm were investigated. The FMR measurements were performed by a vector network analyzer (VNA) technique with scanning frequency at a specified external field. The measured frequency response was fitted well by the theoretical precession conditions. The FMR results show that the effective saturation magnetization, mu M-0(eff), increases from 1.01 to 1.36 T, while the film thickness varies from 30 to 360 nm. A discontinuous transition is observed at the thickness of 90 nm, which corresponds to the transformation boundary of domain wall from Neel to Bloch type in Permalloy films. Meanwhile, the variation of damping coefficient with film thickness also shows a discontinuity at 90 nm. For films thinner than 90 nm, the dampings vary insignificantly with film thickness. For films thicker than 90 nm, the damping coefficient varies linearly with the thickness. The result could be explained by the magnon scattering through nonuniform magnetization.