Magnetic Field-assisted Current-Induced Magnetization Reversal Of CoZr Magnetic Multilayers

In order to meet the requirements of more efficient,stable and low power consumption in the process of information storage and data processing,a new generation of magnetic random access memory based on spin-orbital torques（SOT-MRAM）comes into being,which brings great convenience to human life.The core structure of the SOT-MRAM is the heavy metal/ferromagnetic metal.However,the critical current density of driving the magnetization reversal is still higher than 106 A·cm-2,which greatly hinders the practical development of the device.At the same time,the further reduction of the storage unit leads to superparamagnetic phenomena,which will also be accompanied by problems such as information storage failure.Therefore,it is necessary to develop a new material or technology to reduce the critical turnover current density.In this work,CoZr alloy with high magnetocrystalline anisotropy was studied in detail.Multilayer films of CoZr with varying structures were deposited on Si/SiO2 substrates by a magnetron sputtering technique.We discussed the influence of interface atomic diffusion and charge transfer caused by annealing on the magnetic and spin transport properties of different systems.A hybrid drive method of magnetic field and current was proposed to further reduce the critical current density for magnetization reversal.Then,the behavior of magnetization reversal in different magnetic anisotropy film samples was investigated.The main research conclusions are as follows:1.The Pd/CoZr/MgO heterostructures was prepared,in which the Pd having strong spin-orbit coupling and MgO providing O 2p orbitals.A fter annealing at 325℃ the interfacial crystallization of the film is improved and it has appropriate Co-O bonding,which realizes strong interface orbital hybridization and obtains the strongest perpendicular magnetic anisotropy（PMA）with the effective anisotropy（Keff）of 2.85×106 erg·cm-3.Meanwhile,the effective electron scattering at the interface is enhanced because of the improved crystallization annealed at 325℃,so we got a large ρAH of 0.29 μΩ·cm,and skew scattering is responsible for the anomalous Hall effects（AHE）.Under the assistance of an out-of-plane magnetic field.the magnetization could be fully reversed with a current density of about 104 A·cm-2.It was found that the current-driven magnetization reversal is highly relevant to the temperature owing to the varied spin-orbital torque,and the current-driven magnetization reversal will be more efficient in low-temperature range,while the magnetic field is helpful for the magnetization reversal in high-temperature range.Finally,compared with in-plane magnetization and isotropic heterojunction,the magnetization reversal in the film with PMA is more efficient to reduce the critical current density.2.The Ta/CoZr/Pd/MgO heterostructure was prepared by modifying Ta/CoZr/Pd heterostructure with MgO.Firstly,we found that the films show the strongest PMA with a Keff of 2.38× 106 erg·cm-3 and its ρAH is 0.93 μΩ·cm,because the crystallization of the film is improved after annealing at 375℃.The critical current density of magnetization reversal driven by hybrid mode is related to the PMA.It can be seen that a lower critical current density is needed to drive the magnetization reversal in the heterojunction with a larger Keff.However,the critical current density is higher in the heterojunction with smaller K_eff.