Magnetostriction and complex permeability of [Fe 62 Co 19 Ga 19 /Py] 5 /glass multilayered films

Abstract [Fe 62 Co 19 Ga 19 ( x )/Py(40– x )] 5 /glass multilayered films, where x =0, 5, 10, 15, 20 nm, y = x (nm)/40(nm), and 0≤ y ≤1, were made by the magnetron sputtering method at room temperature. The total number of combined [Fe–Co–Ga/Py] unit-layers was five. The total film thickness ( t f ) was fixed at 200 nm. We have performed two kinds of experiments on these films: (i) the saturation magnetostriction ( λ S ) measurement, and (ii) the complex permeability ( μ = μ R – jμ I ) experiment to find the resonance frequency ( f R ) as a function of external magnetic field ( H E ). By definition, the microwave power absorption P abs at ferromagnetic resonance (FMR) for a metallic conductor is written as P abs = [ ( μ R 2 + μ I 2 ) 1 / 2 + μ I ] 1 / 2 . We define the half-width of the absorption peak Δ f as Δ f ≣ Δ f S +Δ f A , where Δ f S and Δ f A are the symmetric and asymmetric parts in Δ f . The degree of asymmetry, Δ f A /Δ f , of each absorption peak is associated with the structural and/or magnetic inhomogeneity in the film. The main findings from this study are summarized as follows: (A) maximum λ S occurs in the y =1 film, and as y increases, λ S increases; (B) biasing field for magnetostriction decreases greatly by adding Py layers; (C) the magnetostriction sensitivity remains almost constant in the range 0.4 y ≦ 1; (D) μ R increases, as y decreases. Thus, from this study we conclude that among all the [Fe 62 Co 19 Ga 19 /Py] 5 /glass films, the [Fe 62 Co 19 Ga 19 (30)/Py(10)] 5 /glass film should be the most suitable for applications in nano-magnetic switching devices.