Investigation Of A New Type Of Spin-valve And Magnetic Sensor Based On Topological Insulators

In the electronic information age,electronic materials and devices are changing rapidly.The characteristics of electronic devices,such as high speed,low energy consumption and small volume become the worthwhile goals of research.However,a couple of problems begin to bulge when the transistor size is further reduced.The heat dissipation generated by the electric current is difficult to solve,the quantum tunneling effect starts to become apparent,and the Moore's law gradually becomes invalid.As for the solutions,another property of electron-spin is expected to solve the problem of heat dissipation and leakage,and then realizes new high speed,low power consumption and non-volatile transistor.This paper starts with magnetoresistive devices based on topological insulators and its derivative.The research object is spin-momentum locking of the topological surface states.There are some reasons for us to select topological insulators:high mobility,low power consumption,small back scattering probability.Thus,topological insulators has a certain application on the electricity.Topological insulators has layered structure,like graphene.It thus can meet the need for miniaturization.In addition,due to the unique spin properties of the surface state of topological insulators,it can replace traditional ferromagnetic materials.Traditional ferromagnetic materials need magnetic field to implement the spin polarization.For topological insulators,spin can be polarized by a current.Thus,it will satisfy the large-scale application of electronic logic circuit.The main thesis mainly introduces the surface state transport properties of topological insulators,topological insulator-based spin valve devices,transport properties in phase transition system and potential applications in magnetic sensor.Research results could be divided inthe following three parts:?1?Spin valve transistors are fabricated based on BiSbTeSe₂ topological insulator?TI?with enhanced surface mobility??4039 cm2V-1s-1?.The output in our spin valve transistors exhibits a dominant steplike behavior when sweeping the magnetic field to change the magnetization orientation of the Ni₂1Fe₇9 electrode.Most importantly,the ON?low resistance?-OFF?high resistance?state can be even switched when reversing the direction of the dc current.The TI-based spin valve transistors enable the current-directiondependent switching of ON-OFF state,allowing for the applicability in magnetic sensors and spin-logic circuits,and show the potential use of TIs as innovative current-driven spin generators.?2?Quantum phase transition in topological insulators has drawn heightened attention in condensed matter physics and future device applications.Here we report the magnetotransport properties of single crystalline?Bi0.92In0.07?₂Se₃.The average mobility of?1000 cm2V-1s-1 is obtained from the Lorentz law at the low field?<3 T?up to 50 K.The quantum oscillations rise at a field of?5 T,revealing a high mobility of?1.4 × 104 cm2V-1s-1 at 2 K.The topological Dirac fermions are evident by the nontrivial Berry phase in the Landau Fan diagram.The properties make the?Bi0.92In0.08?₂Se₃ a promising platform for the investigation of quantum phase transition in topological insulators.?3?We report the study of a tri-axial vector magnetoresistance in nonmagnetic?Bi1-xInx?₂Se₃ devices at the composition x = 0.08.We show a dumbbell-shaped in-plane?a-b?negative magnetoresistance up to room temperature as well as a large out-of-plane?c?positive magnetoresistance.Magnetoresistance at three directions is about in a-3%?a?:-1%?b?:300%?c?ratio at 2 K.Through both the thickness and composition-dependent magnetotransport measurements,we show that the in-plane negative magnetoresistance is due to the topological phase transition enhanced intersurface coupling near the topological critical point.Our devices pave the way for new room-temperature spintronic applications,for example,vector magnetic sensors.