Investigation On The Magnetism And Transport Property In Flexible CoFeMnSi Thin Films

The wearable and flexible electronic components have important applications in sensors,displays,medical treatments,storages,and etc.The magnetic device is one of the key components among those systems.So it is of great significance to study the flexibility of magnetic materials and their physical properties in bending conditions or under the stress/strain status.As a sensing component,we expect its physical properties to be sensitive to stress/strain.And for storage,display and other components,its performance needs stable.Therefore,the Heusler spin gapless semiconductor(SGS)CoFeMnSi magnetic alloy was selected and their thin films were prepared by magnetron sputtering in our work.Based on the grasp of the intrinsic characteristics of those thin films,the tunable regulations of their magnetic and transport properties caused by stress/strain were investigated.Subsequently,we inserted the bufer layer of two-dimensional layered material to fabricate the Ti3C2/CoFeMnSi structure in order to reduce the sensitivity of the magnetism under bending,and the physical mechanism was also analyzed.The main achievements are shown as below:Firstly,the fluorophlogopite(F-mica)was chose as the flexible substrate because of their flat surface and high-temperature-tolerance character,then the annealed F-mica/CoFeMnSi crystalline thin films at 300? with partial L21 structure were prepared.The intrinsic characteristics show that CoFeMnSi thin film with thickness of 10 nm has a saturation magnetization of 3.5?B/f.u.at 0 K by using Bloch's law fitting and the resistivity exhibits a semiconducting-like behavior within the temperature range from 80 K to 300 K.The values of electrical conductivity(?xx)and carrier concentration(nt)exhibit the SGS behavior.Subsequently,the flexible thin films were obtained by exfoliating the substrate to investigate the influence of tensile strain on the physical properties of thin films.The bending results of transport property show that there exists the bending tunability of the band structure and coercivity(Hc).The resistivity of film with thickness of 10 nm presents a transition from the semiconducting to metallic tendency around a temperature of 225 K under bending.The Hc could also be tuned up to 440%at the maximum bending of tensile strain of 1%Secondly,owing to the particularity and limitation of the acquisition method of F-mica based flexible thin films,aluminum foil(AF),which is widely used,was selected as the substrate to prepare films with the same structure,and the effects of tensile strain and compressive strain on the magnetic property were systematically investigated.The bending results of magnetism show that the Hc also increases after bending.The magnetic anisotropy of thin films can also be tuned,that is,the thin films seem too hard to be saturated along the in-plane direction when realizing tensile strain,and compressive strain makes the opposite effect.The in-plane remanence ratio(Mr/Ms)can be tuned from 0.67 at an initial state to 0.46 under a tensile strain of 0.5%and to 0.91 under a compressive strain of 0.5%in annealed AF/CoFeMnSi(10 nm)thin film at 300?.When the films are flattened again after bending,part of the residual stress has an irreversible effect on the displacement of the domain wall,which causes the slight deviation for the re-flatten film from the initial statusBased on the above-mentioned understanding of the magnetic property of flexible thin films,the AF/Ti3C2/CoFeMnSi thin films were prepared by coating a two-dimensional layered Ti3C2 as a buffer layer on the metallic AF substrate,which significantly reduced the magnetic sensitivity to stress/strain and there are less residual stress after bending.The bending results show that the Hc of the annealed AF/Ti3C2/CoFeMnSi thin films at 300? remains essentially unchanged under the state of stress/strain,and the increasing or decreasing trend of Mr/Ms became slow.The magnetism remain stable after bending for ten times.