Manipulation And Mechanism Of Interfacial Dzyaloshinskii-Moriya Interaction In FM/NM System

For a long time,microelectronic technology has been developing rapidly along the well-known Moore's Law.It is dedicated to studying the properties of electronic charges and controlling the electronic charges used electric field to achieve the processing of information.However,spin is rarely studied.Nowadays,in order to meet the requirements of integration,the size of transistors continues to shrink.The leakage current generated by the quantum effect and the thermal effect caused by it make this law encounter a bottleneck.Therefore,people began to pay their attention to studying the property of spin,hoping to solve this bottleneck by manipulating the amplitude and phase of the spin wave and realize a low-power signal processing scheme.Therefore,spintronics has emerged as a discipline that studies the properties of spin.Nowadays,spintronics has developed into an independent and popular subject.At the same time,spintronic devices are also expected to replace microelectronic devices in the future and lead the new trend of information technology.Recently,the topological properties in the magnetic structure and its related applications are considered to be the information carriers of the next generation of spintronic devices,which is one of the current research hotspots in this field.Skyrmion is a kind of particle-like spin structure with topological protection.Due to its special topological properties,it has many advantages such as small size,stable structure,and low driving threshold current.Therefore,it is considered as an information carrier in a spin storage device with high speed,high density,and low energy consumption,which has attracted widespread attention from the fields of physics to electronics.Similarly,domain walls(DW)are also commonly used as information carriers in storage or logic devices.Devices using them as carriers can achieve a small size,which is expected to solve the contradiction between integration and energy consumption.Generally,a large Dzyaloshinskii-Moriya interaction(DMI)is required to induce such special spin structure.Therefore,DMI has been the subject of intense research in recent years.Such i-DMI can promote noncollinear spin alignments and determine the chirality and dynamics of chiral spin textures.The magnetic skyrmion and domain walls with certain chirality can be stabilized by DMI.Furthermore,DMI can drive skyrmion and domain-wall motion via spin-transfer torques.A larger DMI is desired to decrease the size of these chiral spin textures.Therefore,in-depth study of DMI is of great significance to the development and promotion of skyrmion-based new memory storage devices and Racetrack Memories.In this dissertation,we mainly use the self-built Brillouin light scattering system to study the magnetization dynamics behavior of the magnon to investigate the Dzyaloshinslii-Moriya interaction.The main content is summarized as follows:1.Construction and optimization of Brillouin light scattering systemWe built the required external optical path system of backward-scattering Brillouin light scattering(BLS)based on the data and actual needs in the experiment.The self-built external optical path system removes the non-negligible miscellaneous peaks in the measurement spectrum,and realizes a stronger spectrum signal and a higher measurement efficiency.Besides,the tandem Fabry-Perot interferometer and the microscopic optical system in the Brillouin light scattering system were debugged to make it in the best working condition to meet the requirements of the experiment.We also introduced the working principle of it.The construction and optimization of the Brillouin light scattering system is the basis and key to our in-depth study of magnon dynamics and accurate extraction of DMI intensity.2.Interfacial DMI and Dynamic behavior of Fe/Pt systems grown on different buffer layersBased on the fact that ferromagnetic and heavy metals with strong spin-orbit coupling systems can induce a strong iterfacial Dzyaloshinskii-Moriya Interaction(i-DMI),the self-built BLS system was employed to investigate the i-DMI of Fe/Pt systems on different buffer layers(MgO,Ta and SiO2).The strength of the i-DMI is 0.439 mJ/m2,0.396 mJ/m2 and 0.338 mJ/m2,respectively,which indicates that i-DMI is more sensitive to the contact layer.Ferromagnetic resonance(FMR)experiments show that Fe grown on the MgO buffer layer has good crystalline quality and a smoother interface,resulting in a narrower FMR absorption peak,a smaller Gilbert damping constant and a higher i-DMI energy.Secondly,X-ray diffraction(XRD)revealed a(200)and(110)preferred orientation of Fe on MgO and Pt(Ta,SiO2)buffer layers,respectively,while the strength of i-DMI of MgO/Fe/Pt is about 8%higher than that of Pt/Fe/MgO,which indicates that the crystal orientation also has an effect on the strength of i-DMI.Choosing an appropriate non-magnetic(NM)layer can enhance the energy of i-DMI.These studies have laid a theoretical foundation for people to further analyze and tune DMI,and provide important reference value for the exploration of chiral materials.3.Diversified manipulation of interfacial Dzyaloshinskii-Moriya Interaction in FM/NM systemsWe demonstrate various approaches to manipulate interfacial Dzyaloshinskii-Moriya interaction(i-DMI)in magnetic films based on magnetic dynamic measurements,including Br:illouin-light-scattering and broadband-ferromagnetic-resonance experiments.It is found that i-DMI can be significantly enhanced with the ferromagnet(FM)layer sandwiched between heavy-metal(HM)layers.The induced i-DMI clearly exhibits different chiralities for HM1/FM and HM2/FM,respectively,resulting in enhancement of i-DMI after stacking in a sandwich structure.We show that i-DMI can be greatly increased by capping the HM/FM system with an oxide layer.The strong Rashba effect due to an interfacial electric effect at the FM/oxide interface is responsible for the increased i-DMI.Furthermore,such an i-DMI induced by the Rashba effect can be efficiently tuned by an electric field.Finally,we find that i-DMI can be effectively tailored with a strain,and the strength of i-DMI increases linearly with strain in the sample.We further speculate that i-DMI can be enhanced by more than 100%by combining several approaches demonstrated here.We also find that the extracted i-DMI strength is more accurate by introducing asymptotic values of the gyromagnetic ratio(?)with a frequency approaching infinity from ferromagnetic resonance data.Our findings will benefit the spintronic community in the exploration of novel devices with chirality dependence and definitely pave the way for chirality-based spintronics applications.4.Tunable inter facial Dzyaloshinskii-Moriya Interaction in symmetrical Au/[Fe/Au]n multilayersAccording to traditional theoretical predictions,DMI exists in systems or structures with broken spatial-inversion symmetry.However,by tailoring the chirality of i-DMI at Au/Fe interface,an overall enhancement of i-DMI was obtained in the Au(4nm)/Fe(3nm)/Au(4nm)symmetric structure.Furthermore,the tunability of i-DMI was realized by changing the stacking number n in Au/[Fe/Au]n multilayer structure.A large tensile stress at the bottom of Fe due to the lattice mismatch was responsible for the chirality change in Sub/Au/Fe system was confirmed by High resolution transmission electron microscope(HRTEM)experiments.The First-principles calculations revealed the sign of the spin-orbit coupling(SOC)energy was changed for Au near the interface of Au/Fe under tensile stress,subsequently reversing the chirality of i-DMI from left-handed to be right-handed and confirming our experimental results.Our finds definitely provide a simplest way to tailor and tune the i-DMI in a multilayer system,further extending and benefitng the application of skyrmion-based devices.