| Van der Waals(vdW)layered two-dimensional materials have the characteristics of atomic layer thickness,high-quality interfaces,and easy integration,and therefore have a wide range of applications in electronics,optoelectronics,and spintronics.Among them,vdW two-dimensional magnets have both strong magneto-crystalline anisotropy and weak interlayer magnetic coupling,which have the potential to further reduce the size of spintronic devices and improve device performance,providing a new opportunity for achieving faster and lower-energy-consumption electronic transport.The exchange bias effect plays a crucial role in improving the performance of spintronic devices,as it can improve the spin control efficiency of the device and the signal-tonoise ratio of the spin detection process significantly.Therefore,bringing stable and efficient exchange bias effects into two-dimensional magnets,and achieving effective control and application of exchange bias,is one of the primary tasks in designing and researching new spintronic devices.The interfacial interaction between different magnetic orders is important for introducing and controlling exchange bias.In the two-dimensional magnets,the lack of direct electronic interaction makes the interfacial interaction between two-dimensional materials weaker than that in traditional material systems,which is not conducive to the formation of strong interface pinning effects.However,the weaker interface interaction also endows two-dimensional magnetic materials with more flexible and efficient methods of the control of exchange bias.Combined with the weak interlayer vdW interaction in two-dimensional magnets,efficient control of exchange bias can be achieved by adjusting the interlayer coupling of the ferromagnetic layer,the antiferromagnetic layer or the interfacial interaction between the two.In addition,the exchange bias effect can not only pin the magnetization direction of the ferromagnetic layer but also control the magnetic reversal process.Therefore,optimizing the device structure is a prerequisite for achieving higher performance and more functional spintronic devices.In order to realize the application of two-dimensional magnetic materials in compact and high-performance spintronic devices,this thesis selects the twodimensional ferromagnetic material Fe3GeTe2 with perpendicular magnetic anisotropy as the research object,and uses the two-dimensional interface effect to carry out the study of introduction,control,and application of exchange bias effect in Fe3GeTe2.The main work of the thesis is as follows:1.This thesis introduces efficient and stable zero-field cooling exchange bias effect at the Fe3GeTe2/O-Fe3GeTe2 interface through surface-induced coupling.After low-temperature annealing,a weak antiferromagnetic oxide layer is introduced on the surface of Fe3GeTe2,and the exchange bias field can be reset using isothermal magnetic field polarization.Combining with the results of transport measurements,a physical model of spontaneous exchange bias in this system is proposed.In addition,by sputtering oxide thin film on the surface of Fe3GeTe2,an antiferromagnetic amorphous layer is formed at the Fe3GeTe2/Oxide interface,which realizes a more stable and controllable zero-field cooling exchange bias effect in heterojunctions.This work is the basis for the subsequent works in this thesis,and has important reference value for the research on the control of two-dimensional magnetic materials and the design of twodimensional spintronic devices in the future.2.This thesis selects the Fe3GeTe2/MgO heterojunction structure as the research object and realizes efficient non-volatile control of the exchange bias field and coercive field in the heterojunction using ultra-low electric fields.Via applying gate voltage of 5～20 mV to polarize the heterojunction,significant adjustment of the exchange bias field in the range of 700～0 Oe is achieved.The results of the systematic transport measurements and first-principle calculations show that the electric field changes the interlayer coupling in Fe3GeTe2 by driving the migration of ions at the Fe3GeTe2/MgO interface,thereby achieving effective control of the coercive field and exchange bias effect of the heterojunction by the electric field.The two-dimensional ferromagnetic/non-magnetic oxide heterojunction constructed in this work provides a new approach for achieving efficient magnetic control and designing non-volatile,lowloss nanoscale storage devices.3.This thesis realizes the antisymmetric magnetoresistance and its effective control by optimizing the structure of the magnetic tunnel junction device.The thesis designs an asymmetric Fe3GeTe2/graphite/Fe3GeTe2 structure device,in which stable antisymmetric four-state magnetoresistance is achieved.Through the sysematic transport measurements,the mechanism of antisymmetric magnetoresistance is explored,and effective control of antisymmetric magnetoresistance using exchange bias is achieved based on this.Finally,the thesis demonstrates the multi-state magnetic storage process based on this device.This work provides new ideas for improving the storage density of magnetic storage devices and the application of exchange bias effect in spin valve devices. |
