Static and high frequency magnetic properties of FeGa thin films deposited on convex flexible substrates

In this study, we provided an approach of pre-strained growth to significantly enhance the FMR frequency of magnetic films. A series of 100 nm magnetostrictive FeGa films were grown on flexible polyethylene terephthalate (PET) substrates which were bowed onto the convex molds with different curvature radii. When the FeGa films were flatten to a plane, they were suffered a compressive strain arisen from the shaped substrates. As shown in Figs . 1(a) and 1(b), the FeGa films exhibit a remarkable uniaxial anisotropy perpendicular to the compressive strain. The strength of magnetic anisotropy is enhanced with increasing the compressive strain from 0 to 0 .78%. The permeability spectra measured in the frequency range from 0 .5 to 8 GHz are shown in Figs . 1(c) and 1(d). With the increase of the compressive-strain induced magnetic anisotropy, the initial permeability μ_i of the FeGa films inconspicuously decreases, while the FMR frequency shifts toward the higher values. In order to quantitatively understanding the effect of strain on the dynamic properties of the FeGa thin films, the experimentally obtained permeability spectra can be fitted by using the Landau-Lifshitz-Gilbert (LLG) theory.

Magnetic thin films, when applied in high-frequency devices, are required to have relatively high real and low imaginary permeability, and the ferromagnetic resonance (FMR) frequency need to be higher than the working frequency of the devices. In experiment, the methods including oblique deposition, field annealing, and interfacial exchange coupling, have been often used to increase the magnetic anisotropy and the FMR frequency of thin films. For magnetic films deposited on flexible substrates, because of the magnetostriction, the magnetic anisotropy can be substantially changed by applying mechanical strains [1], [2].