The Study Of Interfacial Spin Transport In Magnetic Heterostructure

Spintronics research aims to add spin degrees of freedom to traditional electronic devices,to explore the possibility of utilizing spin properties instead of charge functions to achieve information recording,operation and reading,and fundamentally solve the problem of high energy consumption of integrated devices.The magnetic heterostructure is the composite structure composed of ferromagnetic metal(FM)or ferromagnetic insulator(FI)and non-magnetic metal(NM)and can simultaneously realize the generation and detection of spin current.It is not only an ideal system to study spin transport related phenomena,but also the core component where the various effect of spintronics is functionalized.In the previous research on spin transport of magnetic heterostructures,people took the spin orbit coupling in NM as the main generation source of spin current,and realized a new strategy of using spin torque instead of magnetic field to read and write information.For instance,damping-like spin orbit torque induced by the Spin Hall effect can effectively regulate the local magnetization state,and it has been well explained at the qualitative level.In order to further highlight the function of related spintronics effect,the magnetic heterostructure is getting thinner and thinner,and the interface effect is becoming more and more significant.As the inherent symmetry of the interface is broken,the new phenomenon produced by the interface under the effect of spin-orbit coupling has revolutionized people's understanding of the field of spintronics.For example,the interface can be used as an independent spin current generator.The spin torque is generated to realize the regulation of the localized magnetization state;the interfacial DMI can form and stabilize the chiral domain structure(skyrmions)in the magnetic material,and provides a new idea for the magnetic recording mode.Therefore,this paper has carried out research work on the interfacial spin transport in magnetic heterostructures,and the main innovative results obtained are as follows:1.A spin accumulation mechanism determined by the competition between the Spin Hall effect and the Anomalous Hall effect in a FM/NM heterostructure is proposed.Interfacial spin accumulation is an important source of spin orbit torque in magnetic heterostructures,but its mechanism is not yet clear.We built the interfacial spin accumulation mechanism determined by the competition of these two effects with the two main sources of spin current in heterostructures,namely the Spin Hall effect in NM and the Anomalous Hall effect in FM;The independent control of Spin Hall effect and Anomalous Hall effect is realized experimentally through sample design,and the main characteristics of this spin accumulation mechanism are verified by the characterization of field-like spin orbit torque.This result not only proposes a clearer interfacial spin accumulation mechanism,but also gives a physical image for the dependence of fieldlike spin orbit torque strength on related material parameters,which deepens our understanding of field-like spin orbit torque.2.It is verified that the spin orbit torque in magnetic heterostructures with structural inversion symmetry is derived from the spin scattering induced by the interface.Understanding and verifying the spin orbit torque in magnetic crystals or magnetic heterostructures with inversion symmetry is currently a difficult problem in the field of Spintronics.In the symmetrical Co/Pt/Co multilayer film,we utilize the symmetry of the structure to offset the spin orbit torque generated by the Spin Hall effect and the interfacial Rashba effect,thereby highlighting the contribution of the interfacial spin scattering;We use the spin rectification effect produced by the acoustic resonance mode in this structure,verifying the existence of this torque and characterizing its peculiarities.Then the quantitative relationship between the torque magnitude and the current intensity is obtained by harmonic measurement.This result not only directly gives experimental evidence of spin orbit torque generated by interfacial spin scattering,but also provides a potential mechanism for generating macro spin orbit torque in single-layer ferromagnets.3.A physical image and experimental method for analyzing the interfacial DMI intensity from the perspective of spin transport in magnetic heterostructures are proposed.Since the interfacial DMI is the core factor for generating and stabilizing the skyrmion and chiral domain structure,the research on the mechanism of the interfacial DMI is the basis for applying chiral domain structures such as skyrmion to spin spintronics devices.Based on the pure spin current transport mechanism in magnetic heterostructures,we constructed a physical image of the correlation between dampinglike spin orbit torque efficiency and interfacial DMI strength,and gave direct experimental evidence.This result breaks through the thinking mode that only considers the interfacial DMI to be associated with a single material parameter,and provides a more comprehensive experimental method for analyzing the interfacial DMI strength from the perspective of spin transport.4.A new mechanism of interlayer exchange coupling based on interfacial spin polarization is proposed.Unlike the interlayer exchange coupling model with oscillation attenuation characteristics based on the principle of quantum interference,we found a long-range ferromagnetic interlayer exchange coupling associated with spin polarization intensity for NM and the interface of FM/NM in Co/Pt/Co multilayer film system.Based on spin transport mechanism in heterostructures,we constructed a new mechanism of magnetic interlayer exchange coupling caused by interfacial spin polarization,obtained the quantitative relationship between interlayer exchange coupling energy and spin polarization intensity and characteristic length of spin polarization through experiments of changing temperature.This result not only extends the microscopic mechanism of interlayer exchange coupling from the perspective of spin transport,but also expands the research on the related effects of spin transport from excitation state properties to ground state properties in magnetic heterostructures.