Ferromagnetic resonance properties of Fe81−xNixGa19/Si(1 0 0) and Fe81−yNiyGa19/glass films

Two series of Fe81−xNixGa19/Si(1 0 0) and Fe81−yNiyGa19/glass films, where x or y = 0–26, were made by the magnetron sputtering method. The film thickness (tf) was fixed at 100 nm. We have performed three kinds of experiments on these films: (i) the saturation magnetostriction (λS) measurement; (ii) the easy-axis and hard-axis magnetic hysteresis loop measurements; and (iii) the ferromagnetic resonance (FMR) experiment to find the resonance field (HR) with an X-band cavity tuned at fR = 9.6 GHz. The natural resonance frequency, fFMR, of the Kittel mode at zero external field (H = 0) is defined as fFMR ≒ ν[HK4πMS]1/2, where γ = 2πν is the gyromagnetic ratio, HK and 4πMS are the uniaxial anisotropy field and saturation magnetization, and HK << 4πMS. The Gilbert damping constant, α, is calculated from the formula, α = [ν(ΔH)S]/(2fR), where (ΔH)exp = (ΔH)S + (ΔH)A, (ΔH)exp is the half-width of the absorption peak around the resonance field HR, (ΔH)S is the symmetric part of (ΔH)exp, and (ΔH)A is the asymmetric part. The degree of asymmetry, (ΔH)A/(ΔH)exp, is associated with the structural and/or magnetic inhomogeneities in the film. The main findings of this study are as follows: (A) fFMR tends to decrease, as x or y increases; (B) α decreases from 0.052 to 0.020 and then increases from 0.020 to 0.050, as x increases, and α decreases from 0.060 to 0.013 in general, as y increases; and (C) λS reaches a local maximum when x = 22. We conclude that the Fe59Ni22Ga19/glass film should be the most suitable for application in magneto-electric microwave devices.

► FeNiGa films are good soft magnetic materials, which can be used in the GHz range.
► As shown in Fig. 2, the FMR’s absorption width (ΔH)exp is not symmetric (ΔH)S.
► The Gilbert damping parameter (α) is calculated from (ΔH)S instead of (ΔH)exp.
► α of the FeNiGa/Si films is less accurate, because eddy current around interface.
► Fe59Ni22Ga19/glass film is good for the microwave magneto-electric device.