| With the development of information technology industries such as artificial intelligence and the Internet of Things,the demand for low-power information technology is growing rapidly.Low-consumption electronic devices are the cornerstone for realizing advanced information technologies in the future.Traditional electronic devices mainly process information through the transfer of electronic charges.The scattering effect in the charge transfer process is the root cause of high energy consumption and high heat generation.Therefore,people have begun to pay attention to the spin properties of electrons to realize spinbased information storage,transmission,and processing,and have tried to design and develop spin electronic devices.The Zeeman effect guided by an external electromagnetic field can manipulate spin motion and is a conventional means to drive spin electronic devices.However,the current intensity required to generate an electromagnetic field is quite large,resulting in significant energy consumption and heat generation.Therefore,researching new magnetoelectric coupling mechanisms,bypassing the dependence on external magnetic fields,and manipulating spin motion through all-electric means(applying current or voltage)to control zero-field magnetization switching,is an ideal path to achieve low-power spin electronic devices,and also one of the important research directions in condensed matter physics.Ferrimagnetic systems have two or more asymmetric magnetic sublattices,which have more magnetic degrees of freedom and potential to realize new physical phenomena compared to ferromagnetic and antiferromagnetic systems,making ferrimagnetic materials attract much attention in areas such as ultrafast optical switching,current-induced magnetization switching,and domain wall motion.Ferrimagnetic materials may be an ideal platform for realizing lowpower,non-volatile magnetization switching,and magnetic memory devices in the future.This paper investigates three aspects of electric field control of magnetization in ferrimagnetic materials,as follows:(1)Based on spin-orbit torque and tilted anisotropy,field-free current controlled magnetization switching is achieved in the CoGd ferrimagnetic alloy.In the Hall device based on the Pt/CoGd/Pt heterostructure,we found that current pulses(pulse width 5 ×10-5 s,current Ix=±18 mA)can induce spin-orbit torque and manipulate magnetization switching of the device at room temperature and zero magnetic field.Magneto-optic Kerr effect and various transport measurements show that the Pt/CoGd/Pt heterostructure grown in this work has unusually tilted magnetic anisotropy and intrinsic in-plane bias field,causing the spontaneous breaking of mirror symmetry in the magnetic structure and eliminating the dependence of spinorbit torque induced magnetization switching on the in-plane auxiliary field.Based on the above considerations and the Landau-Lifshitz-Gilbert equation,we established a ferrimagnetic coupled spin model to simulate the process of spin-orbit torque driven magnetization switching,and gave calculated results consistent with experimental observations,further supporting the tilted anisotropy mechanism of field-free switching.These research results show that the Pt/CoGd/Pt heterostructure deposited by using composite targets is easy to produce spontaneous breaking of mirror symmetry,exhibiting intrinsic tilted magnetic anisotropy and in-plane bias field,providing an ideal platform for achieving spin-orbit torque induced magnetization switching under zero magnetic field.(2)Based on hydrogen ion gate-controlled compensation temperature,field-free voltagecontrolled magnetization switching is achieved in the ferrimagnetic alloy thin film CoGd.First,we successfully prepared the heterostructure of Pt/CoGd/Pt and Hall devices using magnetic sputtering,photolithography,and Air ion milling.Anomalous Hall effect was observed in the ferrimagnetic alloy.The Hall transport signal depends on the handedness of the external magnetic field with the composition(Co-rich or Gd-rich)and measurement temperature of the thin film,showing significant ferrimagnetic characteristics.Secondly,we found that the ionic liquid gate voltage can generate hydrogen ions and oxygen ions,and drive these light ions to be injected(or extracted)into the Pt/CoGd/Pt heterostructure,thereby greatly reducing(or increasing)the compensation temperature of the heterostructure(control range greater than 200 Kelvin),providing the possibility of achieving field-free magnetization switching induced by gate voltage.Due to the differences in free energy difference,ionic relaxation time difference,and bond strength,the hydrogen ion control process driven by positive voltage and the oxygen ion control process driven by negative voltage show very significant differences.Combining X-ray characterization,density functional theory calculations,Heisenberg model,and Monte Carlo simulations,we propose that the main reason for the gate voltage induced the shift of compensation temperature may be that the injected hydrogen and oxygen ions caused charge transfer and orbital rearrangement of Co and Gd magnetic ions,which ultimately greatly inhibited the Gd-Gd exchange coupling,causing Gd magnetization MGd and compensation temperature to decrease sharply.Because the directions of sublattice magnetizations MCo and MGd remain unchanged under zero magnetic field,gate voltage control of MGd will also lead to the reversal of the net magnetization direction,thereby achieving the gate voltage control of field-free magnetization switching.These research results prove that gate voltage control of ion migration is an effective way to achieve magnetization switching.(3)Based on the current control of compensation temperature,field-free current-controlled magnetization switching is achieved in the ferrimagnetic oxide semiconductor Gd3Fe5O12.First,we increased the conductivity of the insulator Gd3Fe5O12 by 106 times through a strong electrical effect,thus achieving a good conductive ferrimagnetic oxide semiconductor at room temperature,creating a prerequisite for achieving the current control of magnetization.Combining experiments with DFT theoretical calculations,we found that strong electrical effects can drive Ag in the electrode into garnet Gd3Fe5O12,causing oxygen defects leading to a reduction in the forbidden band width of Gd3Fe5012,thus reducing the activation energy of semiconductor conductivity and achieving good conductivity in Gd3Fe5O12;the substitution of Ag for the special position Fe suppresses the forbidden band width by>75%,thus reducing the activation energy of semiconductor conductivity and enhancing conductivity.The strongly electrically treated Gd3Fe5O12 becomes an ideal carrier for achieving zero-field current modulated magnetism.Vibrating sample magnetometer measurements show that applying anultra-low current density of 2 mA/cm2 to Gd3Fe5O12 at room temperature can effectively drive the remanence magnetization(0.05 emu/g)to reverse.At the same time,the current can also effectively control the coercive field,with an adjustment range of 40%.The above currentcontrolled magnetization phenomena can be well explained within the framework of current induced compensation temperature.These results indicate that strong electric processing can induce the conductivity of Gd3Fe5O12,thereby achieving field-free current-induced magnetization reversal in ferrimagnetic oxides.The results of this paper have clarified the mechanisms of current-controlled compensation temperature in ferrimagnetic semiconducting oxides,ion-controlled compensation temperature in alloy heterojunctions,spontaneous breaking of mirror symmetry in thin films and other fieldfree electrical controlled magnetization switching.It provides a reference for further in-depth research on the electrical control of magnetism.At the same time,it also demonstrates the application potential of ferrimagnetic systems in future low-energy spin electronic devices.Providing reference for further research on electric control of magnetism,and also proves the potential of ferromagnetic systems in future low-consumption spin electronics applications. |
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