Research On The Magnetic Property Of Wrinkled NiFe Films

With the high-speed development of the electronics industry,new requirements on the materials of electronic devices have been put forward.The disadvantages of traditional rigid materials in mechanical properties have led to the limitations in their application.Therefore,flexible electronic devices have quickly become a new research hotspot in the field of new electronic devices.At present,commercial flexible electronic devices not only retain the excellent performance of rigid devices,but also have the advantages of flexibility,light weight,bendability,and stretchability.They have wide application prospects in many aspects such as communications,medical treatment,and inspection.Wearable electronic devices are inevitably subjected to various tensile external forces during the wearing process,which have great requirements on tensile properties.After a long period of research,the current main method of making stretchable electronic devices is to grow a metal thin film on a pre-stretched elastic substrate.Take use of the large differences of the Young's modulus between the metal thin film and the elastic substrate to fabricate film with large-scale periodic wrinkled morphology.When the wrinkled film is subjected to external stress,it can effectively release the external stress through the expansion and contraction of the wrinkled structure,thereby ensuring the stability of the film performance.Magnetic anisotropy is one of the most important physical properties of magnetic materials.In different types of magnetoelectric devices,the magnetic anisotropy of the magnetic film plays an important role.Therefore,it is very necessary to study the magnetic anisotropy of the magnetic film with wrinkle morphology,but so far there is still a lack of the investigation on surface morphology and magnetic anisotropy of the magnetic film and devices deposited on the biaxial pre-strained PDMS substrate.Many previous studies have shown that the surface structure of one-dimensional wrinkles and oblique growth can effectively improve the magnetic anisotropy of the film,thereby significantly increasing the ferromagnetic resonance frequency of the film.At the same time,the research on the high-frequency performance of magnetic thin films is also a current research hotspot.So far,there is still a lack of magnetic anisotropy and high-frequency performance of magnetic films with wrinkled structure by oblique growth.Based on the above research background,this paper conducted the following research:Firstly,we fabricated Ni₈₁Fe₁₉?NiFe?films with wrinkled morphology on uniaxial and biaxial pre-stretched PDMS substrates,and studied their surface morphology and magnetic anisotropy.NiFe films grown on a uniaxially pre-stretched PDMS show a one-dimensional wrinkled structure and a uniaxial magnetic anisotropy along the wrinkles.In contrast,NiFe films grown on a biaxially pre-stretched PDMS show a two-dimensional zigzag wrinkled surface morphology and a uniaxial magnetic anisotropy which direction is determined by the sequence of releasing the biaxial pre-stresses.The wavelength and the amplitude of the wavy morphology for both the1D and 2D wrinkled NiFe thin films decreases and increases with improving the growth pre-strain,respectively.The uniaxial magnetic anisotropy of the wrinkled NiFe films originates from a surface effect of magnetic charges created on the wavy topography when a magnetic field is applied.Secondly,in this paper,a one-dimensional wrinkled film was fabricated by growing metal Ta on a uniaxial pre-stretched flexible polydimethylsiloxane?PDMS?substrate and then Ni₈₁Fe₁₉ films were grown by oblique sputtering.By studying its surface morphology,we can control the wavelength and amplitude of the wrinkled structure by applying different growth pre-strains.At the same time,it can be found that wrinkle structure can induce a uniaxial magnetic anisotropy along the wrinkles,and it increases with the increasing of growth pre-strain.The relationship between the coercive force and the angle of the external magnetic field was studied through the VSM rotation angle test.It was found that the magnetization reversal mechanism of the NiFe thin film tends to a two-phase model.Finally,the high-frequency performance was characterized.The resonance frequency of the magnetic spectrum increases with the increase of growth pre-strain.Finally,the tensile fatigue test shows that the wrinkled structure can effectively maintain the stability of NiFe film's high-frequency performance.Finally,the research content of this paper is summarized and put forward some meaningful work prospects.