Study Of Spin-Dependent Transport Properties In Co-Based Multilayer By Interfacial Manipulation

With the rapid development of 5G communication,big data,cloud computing,blockchain.autonomous driving,artificial intelligence and other fields,the demand for storage components,sensor devices and logic devices,etc.shows exponential growth.But with the failure of Moore’s law,semiconductor electronics of the postMoore era have gradually failed to keep up with demand,spintronics devices have gained a lot of attention because of their non-volatile,fast read/write,high endurance and low power consumption.However,most of the spintronics devices are still in the lab stage,and the performance is far below the demand of practical applications,and only a few of them can be used in some cutting-edge fields.Therefore,how to effectively modulate the performance of spintronics devices and investigate their physical origin are crucial for both theoretical research and practical applications of spintronics.Currently,spintronics devices are mainly based on nano-multilayer structures such as heavy metal/ferromagnetic layers,where the core structure is mostly Cobased ferromagnetic layers,such as Co,CoFe,CoFeB,etc.It is important to modulate the spin-related transport properties of the multilayers by optimizing the Co-based multilayers at the interface for the structural design and performance optimization of spintronics devices.The main research contents and results are as follows:(1)The different oxygen migration behaviors of CoFe/MgO and CoFe/HfO2 interfaces were investigated,and it was found that the magnetic anisotropy of Ta/CoFe/MgO films decreased after annealing,while that of Ta/CoFe/HfO2 films increased.It was found that the Fe-O bonds exist at both CoFe/MgO and CoFe/HfO2 interfaces at as-deposited state,due to the oxidation of interfacial Fe atoms during the deposition of the MgO and HfO2 layers.After annealing,the amount of the Fe-O bonds at the CoFe/MgO interface decreases,whereas at the CoFe/HfO2 interface increases.indicating that the oxygen atoms migrate from FeO bonds to MgO layers at the CoFe/MgO interface whereas from HfO2 layer to FeO bonds at the CoFe/HfO2 interface.Correspondingly.the magnetic anisotropy energy decreases in Ta/CoFe/MgO film but increases in Ta/CoFe/HfO2 film after annealing.We attributed these results to interfacial Fe 3d-O2p orbital hybridization modulated by the different oxygen migration behavior.(2)The efficiency of the spin-Hall spin-orbit torque(SOT)in perpendicularlymagnetized Pt/Co/MgO films can be engineered by introducing ruthenium(Ru)impurities into the bulk of the Co layer.With the increase of Ru doping.the effective field of the damping-like SOT per current density increases by a factor of 2.3 and the SOT efficiency increases by 125%.However,the effect of Ru incorporation on the field-like SOT efficiency is rare.First-principles calculations show that Ru incorporation can significantly increase the major-spin density of states at the Fermi level,but has less effect on the minor-spin density.We suspect that this electronic structure modulation may reduce the bulk spin scattering inside the Co-Ru layer and thus improve the SOT efficiency.We also observe a similar enhancement of SOT by Ru incorporation in Ta/CoFeB/MgO films.(3)Interfacial engineering to modulate the SOT and unidirectional spin Hall magnetoresistance(USMR)in Co-based multilayers was investigated,and the enhancement of SOT and USMR in CoFe multilayers was studied by introducing Pt and Ta layers with opposite spin Hall angles.It was found that the USMR of the Pt/CoFe/Ta was improved by 33%compared with that of the Pt/CoFe,while the USMR of the Ta/CoFe/Pt was improved by 90%compared with the Ta/CoFe.The effective field of the damping-like SOT per current density of the Pt/CoFe/Ta structure was also improved by 50%.Our study utilizes interface engineering to enhance the SOT and USMR of metallic multilayer films through the combination of opposite spin Hall angle materials.(4)Thermal annealing to modulate the SOT and USMR of Co-based multilayers was investigated,and the SOT and USMR in Pt/CoFe/Ta trilayers and Pt/CoFe and CoFe/Ta bilayers at the as-deposited and annealed states were measured and analyzed.It is found that thermal annealing has a great influence on the magnitude and sign of the SOT and USMR in Pt/CoFe/Ta tri layers,and both the damping-like SOT and USMR decrease with the increase of annealing temperature,and they even reverse their sign in the annealing temperature range of 235℃265℃.On the contrary,no sign change of SOT and USMR in the Pt/CoFe and CoFe/Ta bilayers was observed after annealing.Our study implies that the sign of the SOT and USMR in Pt/CoFe/Ta trilayers can be tuned by thermal annealing.