Current-induced Magnetism/electric-field Control Of Magnetism In Perpendicularly Magnetized Heterostructures

With the advent of the era of big data,making the current information storage technology faces many severe challenges.Therefore,the information storing memory with non-volatile,higher read/write speed,high storage density,high stabilization and low consumption,device miniaturization are the main developing trends,magnetic random access memory(MRAM)is expected to become the candidate of the next-generation information storage due to the above advantages.In a heavy metals/ferromagnetic(HM/FM)structures with perpendicular magnetic anisotropy(PMA),the spin-orbit coupling of HM can enable pure spin current generation when passing an in-plane charge current in HMs.Then the polarized spins can work on the magnetic torque and domain wall of adjacent FM layer by the efficient spin-orbit torque effect.However,magnetization switching through SOT can be achieved only when the applied current density larger than the critical current density(~10~6 A/cm~2),this will cause a significant increase in energy consumption.In contrast,through voltage control of magnetic properties in films with PMA can significantly decrease the effect of the joule heat,it can realize magnetization switching with low power consumption.The application of local voltage provides the feasibility for realizing high-density information storage devices with higher stability and lower energy consumption.It is achieved by controlling the migration of oxygen vacancies.However,the domain wall movement driven by the current-induced spin orbit torque(SOT)is closely related to the chiral nature of the spin texture,which means Dzyaloshinskii-Moriya interaction(DMI).In the magnetization switching driven by SOT,when an external magnetic field is applied,the motion velocity of the domain wall can be increased and decreased under the action of DMI.This property plays a key role in the application of spin electrons.Therefore,the magnetic properties of thin films with perpendicular magnetic anisotropy under current and voltage conditions are studied in this paper,as follows:Three systems of Pt/Co/Ta,Pt/Co/CoO/Ta and Pt/Co/TaO_x were prepared and the effects of different interface states on Dzyaloshinskii-moriya interaction(DMI)strength,SOT efficiency and domain wall motion were studied.The results show,for the above three systems,there is a significant difference between the DMI strength and the SOT efficiency with the different interface structures.Comparing the SOT efficiency of different systems,the introduction of CoO makes the oxygen concentration gradually decreases from the Ta/CoO_x interface to the interior of the Co layer,the additional increase in the asymmetry of structural inversion cause the Rashba effect at the interface has been increased,then producing additional SOT which leads to the enhancement of SOT efficiency.In addition,the experimental results show that the interface is the main factor affecting the strength of DMI.The DMI can increase with the exist oxided layer and the increased extent of oxided layer,that is Co/TaO_x>Co/CoO/Ta>Co/Ta.And,the change of domain wall motion with current drived in different system samples is shown as follow:CoCoO/Ta>Co/Ta>Co/TaO_x,the lower speed of domain wall is related to the increased pining barrier,and with the current induces the moving process of the domain wall,the joule heat is generated by the current that have a great impact on its movement speed,and further increased current density will lead to multiple nucleation in the sample,thus reducing the rate of domain wall movement.These phenomena provide a new idea for further improving the SOT efficiency and the strength of DMI,and also provide a new understanding for further understanding the domain wall movement driven by current-induced SOT.The magnetic signals and domain wall images for Pt/Co/Ta/TaO_x/Pt and Pt/Co/CoO/Ta/TaO_x/Pt at different voltages are characterized,and the magnetic changes of samples under voltage conditions are discussed.From the analysis of the experiment results,it can be seen that the manipulation of the Coercivity field by the applied voltage is owing to position change of the oxygen vacancy in the sample.At the same time,the change of magnetic moment switch under different voltage size and direction can be directly observed in the domain wall image.It also shows voltage regulation magnetic moment switch not only reduces the influence of joule heat on magnetic moment reversal,but also eliminates the influence of the Oster field generated by the current,in addition,it is also known from the experiment that the regulation of voltage to the sample can be controlled in a small range,which provides a new thinking path for further study of low power consumption and miniaturization of magnetic memory parts.