Investigation On Electromagnetic Characteristics And Modulation In GdFeCo Ferrimagnetic Thin Film

Magnetic random access memory is a device that uses the change of magnetization direction to store,read and operate information.The development of electronic information technology devices toward to low energy consumption,high performance,non-volatile and miniaturization,researches on magnetic random access memory have rapidly developed.Generally,magnetic random access memory stores and reads information by controlling the magnetization reversal of ferromagnetism materials through a magnetic field/current.While these devices have characteristics such as fast read and write rates and non-volatility,their ability to resist external magnetic field interference is weak.Compared with ferromagnetism materials,antiferromagnetism materials have strong ability to resist external magnetic field interference.However,the zero net magnetization makes antiferromagnetism materials difficult to manipulate and cannot be used in magnetic random storage devices.Ferrimagnetism materials have the characteristics of non-zero net magnetization and strong resistance to external magnetic field interference,resulting in they are a good choice for magnetic media in magnetic random access memory.At the same time,magnetic/current control of magnetization has Joule heat,while electric field control avoids Joule heat caused by charge current and reduces energy consumption in magnetic random access memory devices.Therefore,electric field control of magnetization has a good development prospect.However,the shift of magnetization controlled by electric field is small.How to realize the reversal of magnetization controlled by electric field is a problem to realize low-power magnetic random access memory.Based on the above analysis,this thesis takes the ferrimagnetic（FIM）alloys composed of rare earth-transition metal（RE-TM）as the research object,and carries out a series of research work around the spin orbit torque（SOT）and electric field control/assisted magnetization reversal in FIM film.The main innovative achievements are as follows:1)The measurements of temperature-dependent spin orbit torque in single-layer GdFeCo thin films have been achieved.The spin orbit torque of single-layer GdFeCo thin films was measured using spin torque ferromagnetic resonance technology,achieving the measurement of spin orbit torque in single-layer thin films.The measurements of composition gradient indicate that the spin orbit torque of single-layer GdFeCo thin films comes from the Gd composition gradient in the volume space symmetry breaking and the spin Hall effect induced by Gd sublattice magnetic moment.Temperature-dependent measurements of spin orbit torque indicate that the effective field components of spin orbit torque along the y-axis（x-axis）direction diverge（remain unchanged）near the magnetic compensation temperature.The results also show that the spin orbit torque of single GdFeCo film acts on the total magnetization.These results provide experimental reference for studying the spin properties of single-layer ferrimagnetism films.2)This work achieves the control of magnetic compensation temperature and spin orbit torque in GdFeCo thin film by changing the exchange coupling strength.Temperature-dependent abnormal Hall curves of GdFeCo films sputtered at different oblique sputtering angle under different temperatures were measured.It was found that the compensation temperature of GdFeCo thin film was changed with oblique sputtering angle,and the saturation magnetization and effective vertical magnetic anisotropy also changed.What indicates that oblique sputtering can regulate the magnetism of ferrimagnetism materials.The difference of exchange coupling strength between sublattices indicates that the direction of sublattice magnetic moment has different dependencies on the oblique angle.The change in magnetic compensation temperature also causes the difference in spin orbit torque and effective spin Hall angle in single-layer GdFeCo films.This work provides a new method for controlling the magnetic compensation temperature and spin orbit torque of ferrimagnetic films.3)This work achieves the non-volatile transport characteristics of ferrimagnetism materials controlled by electric field.In the Pb(Mn_1/3Nb_2/3)O₃-Pb Ti O₃（PMN-PT）/GdFeCo/Pt heterostructure,it was found that electric field induced the changes in transverse resistance.The transverse resistance measurements under different pulse electric fields indicate the existence of non-volatile transport characteristics in the heterostructures.The transverse resistance and ferromagnetic resonance field controlled by electric field exhibit a"Butterfly-like"curve behavior.These results indicate that the non-volatile electrical transport characteristics controlled by electric field come from the magnetoelectric coupling effect caused by strain in the heterostructure.This work provides a reference for the physical mechanism of electric field-controlled ferrimagnetic films and the study of non-volatile and multi-states memory devices.4)This work achieves electric field-controlled magnetic compensation temperature in ferrimagnetism materials.In the PMN-PT/Ta/GdFeCo/Cu heterostructure,it was found that the polarity of abnormal Hall curve changed as an electric field was applied.The measurements of the anomalous Hall effect under different electric fields indicate that electric field-controlled magnetic compensation temperature exhibits a"Butterfly-like"behavior.This result indicates that the magnetic compensation temperature controlled by the electric field comes from the magnetoelectric coupling effect caused by strain.The first principle calculation shows that the essence of strain-controlled magnetic compensation temperature is the change of exchange coupling strength between sublattices.By designing PMN-PT/Ta/GdFeCo/Ir Mn/Cu heterostructures,electric field control of the exchange bias field at the GdFeCo/Ir Mn interface was achieved.This work provides experimental and theoretical references for achieving electric field-controlled magnetic compensation temperature in ferrimagnetism materials.