Study Of The Interfacial Manipulation On The Spin-Dependent Transport Properties In Nanoscale Multilayers

The spintronics-based devices,which utilize the "spin" of electrons to access the information,are inherently non-volatile and low power consumption due to the absence of the charge accumulation,and are expected to be alternatives to the semiconductor devices.In recent years,many novel spintronics-based devices are emerging,such as the magnetic random access memory based on the spin-orbit torque(SOT)and the magnetic sensor based on the anomalous Hall effect(AHE).The core structure of these devices is the ultrathin magnetic multilayers.The appearance of these devices not only enriches the application field of spintronics,but also brings great changes to the people's life.However,in order to meet the increasing needs of people,the size of these devices demands to be scale down to the nanometers.The reduction of the size could induce the quantum effect,which would impede the further development of the spintronics-based devices.Many researches try to solve this problem by searching a better alternative material in multilayers.But the interface effect related to the size and dimension of the multilayers has always been ignored.When the thickness of the films is reduced to a few nanometers,many interfacial effects,such as interfacial charge transfer,interfacial electron orbital hybridization,and interfacial atoms diffusion,could play a more important role in determining the properties of the multilayers.Therefor in this dissertation,the change of the interface structure on the spin-dependent transport properties in magnetic multilayers were studied.The mainly research results are as follw:(1)A large enhancement of SOT efficiency achieved by introducing 0.2 nm Ti insertion between the Ta and CoFeB layer was demonstrated.The resultant critical current density of magnetization switching was decreased significantly,and deterministic magnetization switching in the absence of an external magnetic was obtained.Interfacial analysis results revealed that the TiB2 formed at the Ta/CoFeB interface as an ultrathin barrier suppressed the Ta diffusion,leading to the improved interfacial spin transparency,which was the main reason of the enhanced SOT efficiency.(2)The effect of the interfacial charge transfer on the SOT was studied.The tunable correlation between the damping-like torque(DLT)and field-like torque(FLT)were demonstrated in Pt/Co/HfO2 multilayers with different annealing temperature(Ta).With increasing Ta,the FLT decreased monotonously while the sign and magnitude of DLT were both changed.Interfacial analysis results revealed that the tunable correlation of them was strongly dependent on the interfacial electron structure between the Co and HfO2 layer.The interfacial charge transfer between the Co,O and Hf atoms could modify the interfacial spin-orbit coupling and crystal electric field,which promoted the interface-generated SOT.This work demonstrated an effective method to tune the correlation of the two SOT components,a desirable feature which would be benefit for the design of SOT-based devices.(3)A large enhancement of SOT in perpendicular Ta/CoFeB/MgO multilayers with interfacial H+and O2-ions manipulation was demonstrated.By controlling both H+and O2-ions at the CoFeB/MgO interface,the switching current density was almost half of that for the single O2-ions manipulated sample.Through harmonic measurements,we have found that both damping-like effective field and field-like effective field were increased for the H+and O2-ions manipulated sample.Interfacial structural results indicated that the H+and O2-ions manipulation modulated the interfacial chemistry at the CoFeB/MgO interface,which suppressed the spin reflection and improved the spin absorption in CoFeB layer.(4)Improved weak magnetic field detection has been achieved by the ultrasensitive linear Anomalous Hall effectin MgO/CoFeB/X/Ta/MgO(X:Hf or Gd)multilayers.The Anomalous Hall sensitivity(Sv)has been tuned by effective oxygen migration assisted interfacial oxygen atoms redistribution.For sample with 0.2 nm Hf insertion,the value of Sv was 16182 ?/T at as-deposited state,560%larger than that of the sample with no insertion(2470 ?/T).However,the value of Sv for the sample with 0.2nm Gd insertion was only up to 6837 ?/T.An ultrahigh value of Sv(28282 ?/T)was obtained for sample with 0.2 nm Hf insertion by further annealing process.Interfacial structural results indicated different linear AHE behavior originated from the various interfacial oxygen atoms distribution state,which can be ascribed to different oxygen migration process.The strong oxygen affinity capability of metallic Hf induced the bidirectional interfacial oxygen migration.However,only unidirectional interfacial oxygen migration can be observed in the sample with 0.2nm Gd insertion.