Investigation On Perpendicular Magnetic Anisotropy And Current-driven Magnetization Switching Of Co-based Multilayer Films

Current information storage technologies are facing many challenges with the advent of the big data era,and non-volatile information storage with low operating power consumption,high storage density,high read speed,and miniaturization has attracted more attention.Amongthese information storage,magnetic random access memory(MRAM)has become a key research direction because of its huge potential and wide application prospects.At present,the research on MRAM is mainly focused on SOT-MRAM based on Spin Orbit Torque(SOT).The principle isthat in the heavy metal/ferromagnetic metal heterojunction with perpendicular magnetic anisotropy,the heavy metal layer will have spin-orbit coupling,which converts the charge flow into a spin current and acts on the magnetic moment,forming the effect of SOT on the magnetic moment.But in SOT-MRAM,in order to realize the current-driven magnetization reversal for storage,the current critical reversal current density is still relatively high.However,the use of electric fields to control the magnetic properties of ferromagnetic metals can effectively reduce the effect of Joule heating and reduce the energy required for current-driven magnetization reversal to a greater extent.At the same time,compared with the easy divergence of the magnetic field,the electric field has better handling stability and convenience that can be applied locally.In summary,storage devices based on voltage-controlled magnetic properties are expected to achieve higher stability and lower energy consumption.In this study,the magnetic properties,transport properties,current-driven magnetization reversal and the regulation of the electric field on the magnetic properties of the Co-based magnetic multilayer film are mainly studied.The research contents are as follows:(1)By changing the film deposition conditions,the Ta/Pt/Co/Ta multilayer film with smaller surface roughness was optimized,and the magnetic and transport properties of the multilayer film with different Co layer thicknesses were characterized,a hysteresis loop and an anomalous Hall curve with good squareness were obtained,indicating that the multilayer film has good perpendicular magnetic anisotropy.By measuring the change curve of the Hall resistance with the in-plane magnetic field,the anisotropy field values of different samples were obtained,and the current-driven magnetization reversal was realized at room temperature.In addition,the effect of electric field on the coercivity and magnetic properties of the multilayer film was studied by applying voltage to the multilayer film.(2)By replacing the top layer material,a high-quality perpendicular magnetic anisotropy Ta/Pt/Co/MgO multilayer film with a small surface roughness under the best conditions was prepared.The curve of the Hall resistance with the in-plane field was measured and fitted to it to obtain the anisotropic field of different samples and obtain a magnetic heterojunction with good thermal stability(large anisotropic field),the corresponding critical magnetization switching current density is on the order of 10⁷A/cm2,indicating that an excessively high anisotropy field will increase the difficulty of magnetization switching.(3)The top layer of WO₃ is grown on the Ta/Pt/Co/MgO multilayer film with better performance,and the Ta/Pt/Co/MgO/WO₃ multilayer film is obtained.After characterizing its magnetic properties and transport,a magnetic multilayer film with good perpendicular magnetic anisotropy was obtained.In addition,the anisotropic field is fitted by the change curve of the Hall resistance with the in-plane magnetic field,and the effective control of the magnetic properties such as the coercive field by the electric field is realized by the gate voltage.