Magnetic Anisotropy And High-frequency Behavior Of Flexible Magnetic Films

With the development of information technologies,electronic systems develop towards to a direction of miniaturization,integration and high frequency.The thin film of magnetic materials is the foundation to achieve the micro magnetic electronic device.Flexible magnetic thin films with polymer thin films as substrates can be bent and have advantages of impact resistance,light weight,low cost and low power consumption.Magnetic anisotropy of magnetic thin films includes magnetocrystalline anisotropy,stress magnetic anisotropy and shape magnetic anisotropy.The resonance frequency of magnetic thin films is decided by the saturation magnetization and the magnetic anisotropy field,we can tune the resonance frequency of magnetic thin films via tuning the magnetic anisotropy field of magnetic thin films.Winkled structure is a key to achieve the stretch of magnetic electronic device and enhance the magnetic anisotropy of magnetic films.The surface morphology of flexible magnetic thin films is related to the fabrication method,thickness of thin films and prestrain of substrates.Firstly,we studied two methods to fabricate flexible wrinkled Fe₈₁Ga₁₉?FeGa?thin films.The one method is to deposit Ta and FeGa directly on a pre-strained polydimethylsiloxane?PDMS?substrate,then relax PDMS pre-strain,which forms a winkled morphology and produces a weak magnetic anisotropy due to the dipolar interactions by surface charges.The other method is to deposit Ta on a pre-strained PDMS,then relax PDMS pre-strain and forms the wrinkle morphology,then deposit FeGa,which produces an obvious magnetic anisotropy due to the resident stress and the shape anisotropy by FeGa inhomogeneous thickness.Secondly,we use the above second method to obtain a wrinkled Ta/PDMS substrate with a sine wavy surface,then we obliquely deposited Fe₆₀Co₂₆Ta₁₄?FeCoTa?thin film to obtain a periodic wrinkled magnetic thin film with a wavy surface deviating of a sine function.At the same angle of oblique sputtering,with increasing the PDMS pre-strain,the wavelength of the surface morphology of FeCoTa thin films decreases and the amplitude increases,the magnetic anisotropy and the resonance frequency increases,the magnetic permeability decreases.At the same PDMS pre-strain,with increasing the angle of oblique sputtering of magnetic thin films,the wavelength and the amplitude of the wavy morphology of magnetic thin films keep unchangedbasically,but the asymmetric of the wavy morphology becomes more obviously,which makes the two phase formation,the magnetic anisotropy of magnetic thin films increases,there are two peaks in the imaginary magnetic spectrum.The resonance frequency cannot be calculated,the real permeability decreases.Thirdly,we deposited the FeCoTa thin films on the polyvinylidene fluoride?PDVF?substrates and researched the thermostability of the magnetic anisotropy of magnetic thin films.When we deposited FeCoTa thin films without oblique sputtering on PVDF substrates,we use the anisotropy of thermal expansion coefficient of PVDF substrates to produce a internal stress to tune the magnetic anisotropy when the temperature changes.We obliquely deposited FeCoTa thin films to enhance a in-plane magnetic anisotropy.We coated a photoresist layer on the surface of magnetic films to bound the expansion and contraction of PDMS substrates when the temperature changes,which decreases the effective strain transfer efficiency between the substrate and the magnetic thin film.