The Study on Ferromagnetic Resonance Linewidth for NM/80NiFe/NM (NM=Cu, Ta, Pd and Pt) Films

The out-of-plane angular dependence of ferromagnetic resonance (FMR) was measured for NM/80NiFe(Py)/NM (NM=Cu, Ta, Pd and Pt) films with various Py, Cu and Ta thicknesses fabricated by magnetron sputtering. The out-of-plane angular dependences of FMR resonance field and linewidth were analyzed using Landau-Lifshitz-Gilbert equation taking account of broadening of linewidth due to magnetic inhomogeneities in a film. Magnetic inhomogeneities were assumed to be the fluctuation of magnitude and direction of the effective demagnetization field which contains both demagnetization and perpendicular anisotropy field for a film. The calculations of the angular variations of linewidth agreed with the experimental ones quantitatively. The fluctuations of magnitude and direction of the effective demagnetization field, which are represented as Δ(4πM_eff.) and Δθ_H, respectively, increased with decreasing Py thickness for all NM/Py/NM films. Δθ_H increased as the thicknesses of the buffer layers increased for Cu/Py(40 Å)/Cu films and was almost constant with increasing buffer layer thickness for Ta/Py(40 Å)/Ta films. Only in the case of NM=Pd and Pt films, the Gilbert damping parameter, which is the speed of decay of magnetization precession, was enhanced significantly as compared with that for the bulk sample and was dependent on Py thickness.