Modulation Of Static And High Frequency Magnetic Properties Of Fe₈₁Ga₁₉ Thin Films Deposited On Flexible Substrates

Magnets have unique magnetic properties with spontaneous magnetization, and coupling effects will be produced when subjected to strain, thermal, electricity, light, etc. Modulation the magnetic anisotropy of thin films by mechanical stress is important for their applications in spintronic devices. Magnetostrictive effect refers to the change of the magnetization state of the magnetic materials with the applied magnetic field. Mangetostrictive effect has been widely used in magnetic/stress sensors, actuators, linear motors, etc. Magnetic anisotropy is one of the most important intrinsic properties of magnetic materials, which determine not only the orientation of magnetization, the magnetostrictive response to magnetic fields and external strain, but also the resonance frequency of electromagnetic devices. Compared to the previously works which focus on magnetostrictive thin films conducted on rigid substrates, magnetic thin films deposited on flexible substrates can be shaped into arbitrary geometries have attracted broad attention. Thin films deposited on flexible substrates may enhance the magnetic response of films to the external mechanical stress due to the deformability of flexible substrates. In this work, the effect of strain on the magnetic anisotropy and high frequency properties of Fe81Ga19 thin films were studied. Moreover, the effect of fabrication method and film thickness on magnetic anisotropy of Fe81Ga19 films deposited on flexible polydimethylsiloxane(PDMS) substrates were also investigated.Magnetostrictive FeGa thin films were deposited on the bowed flexible polyethylene terephthalate(PET) substrates which were fixed on the convex mold. A compressive stress was induced in FeGa films when the PET substrates were shaped from convex to flat. Due to the effect of magnetostriction, FeGa films exhibit an obvious in-plane uniaxial magnetic anisotropy which enhanced with increasing the applied pre-strains on the substrates during growth. Consequently, the ferromagnetic resonance frequency of the films was increased sharply, but the corresponding initial permeability was decreased. Our investigations demonstrated that via the pre-strained substrates is a convenient method to tune the high frequency properties of magnetic thin films, which could be applied in flexible microwave devices.Two methods of fabrication the wrinkled-based patterned magnetic Fe Ga thin films based on the elastic polydimethylsiloxane(PDMS) substrates were investigated. Both the thickness and the preparation process of FeGa thin films affect the magnetic properties and the corresponding surface topography of the films. FeGa thin films deposited on the nano-wrinkled surface which was induced by Ta layer show an obvious enhancement of the uniaxial magnetic anisotropy compared to deposition of Ta and FeGa thin films on PDMS directly. Moreover, the thickness of FeGa films dependence of the uniaxial magnetic anisotropy was also studied.The effect of film thickness on magnetic properties and magnetostriction constant of polycrystalline FeGa thin films were studied. The anisotropy field Hk of flexible FeGa films enhanced with increasing the tensile strain applied along the easy axis of the thin films, but this enhancement via strain becomes unconspicuous with increasing the thickness of FeGa films. The anisotropy field contributed by the surface of FeGa film and obtained by MOKE is smaller than that contributed by the film volume and measured by VSM. We ascribed the difference in Hk to the relaxation of the effective strain applied on the films with increasing the thickness of films.