Investigation On Surface Mophology And Magnetic Property Of Flexible NiFe Films And NiFe/IrMn Exchange Biased Heterostructures

Stretchable electronic devices have the advantages of flexibility,wearability,low cost manufacturing,etc.,and have important application prospects in the fields of information,medical care,energy,and the like,and thus have attracted widespread attention in recent years.The stretchable magnetoelectronic devices refer to a magnetic electronic device having a functionalized thin film prepared thereon by using a macromolecular elastic material as a substrate.The flexible magnetic film with surface periodic structure has properties different from that of the flat rigid magnetic film.The surface morphology of the flexible film can be regulated by the film thickness,substrate pre-strain,etc.,and then the magnetic properties of the film can be controlled.The reason why the periodic structure of the flexible film surface is formed is due to the large Young's modulus difference between the elastic polymer substrate and the metal film,so the interface of the metal film grown on the prestrained elastic substrate releases its prestrain after the interface.The mechanical instability often results in surface periodic fold structures.The magnetic properties of magnetic films with different pleated structures on an elastic polymer substrate were studied,which provides a meaningful basis for the development of stretchable magnetic electronic devices.It has been found that depositing a magnetic thin film on a uniaxially prestrained elastic substrate induces in-plane uniaxial magnetic anisotropy.However,studies on the surface morphology and magnetic properties of metallic magnetic films grown on biaxially prestrained elastic substrates have not been studied.Based on the above background,this dissertation focuses on the magnetic regulation of magnetic films and exchange-biased heterojunctions by different prestrained methods.The work on film preparation,morphology analysis,and magnetic investigation has been carried out and some research progress has been achieved.The main research work can be summarized as follows:Firstly,we prepared NiFe thin films with different pleat morphology on the PDMS substrate by two different prestrained methods,and studied their magnetic properties.For NiFe thin films deposited on uniaxially prestrained substrates,they exhibit a one-dimensional wavy morphology,and there is a weak uniaxial magnetic anisotropy and the easy axis is parallel to the wavy structure direction.However,when the NiFe thin film is deposited on an equal-biaxial prestrained substrate and the pre-strains in the two directions in the plane are released in order,a two-dimensional zigzag surface topography can be obtained.It also has a weakly uniaxial magnetic anisotropy and the easy axis is perpendicular to the first release prestrain direction.Secondly,we prepared NiFe/IrMn exchange-biased heterojunctions with different wrinkling morphology on the PDMS substrate by two different prestrained methods,and studied the angular dependence of their exchange bias field.It is found that the uniaxial prestrain deposited NiFe/IrMn exchange bias heterojunction and the exchange bias direction are parallel to the direction of the stripe structure.The angle dependence of the exchange bias field is basically the same as that of the heterojunction on the silicon substrate.However,when the exchange bias direction is perpendicular to the stripe structure direction or NiFe/IrMn exchange bias heterojunction grown using biaxial prestrain.Although the size of the exchange bias field(H_eb)is substantially equal to that of the growth on the silicon substrate,due to the uniaxial magnetic anisotropy caused by the surface morphology,the angular dependence of the exchange bias field is different from that of the heterojunction on the silicon substrate.