Study On The Spin Transport Properties And Spin Dynamics In Magnetic Thin Films

The 21st century is an information age represented by computers and mobile phones,and it is an era of explosive growth of big data.However,as 5G technology becomes ever more prevalent and the capability of data transmission has been greatly enhanced,it turns into an intractable problem contemporarily to store and process an enormous amount of data.It is also one of the reasons why many countries attach great attention to the innovation of chip technology nowadays.The industry of various CPUs and memory chips such as SRAM and DRAM is based on semiconductors with magnetic materials as the subsidiary.As elementary particles,electrons not only have charge,but also spin.The freedom of charge has been commonly utilized throughout the semiconductor industry,but the freedom of spin is still left to explore,which might also provide the possible development of more integrated electronic devices in the future.The discovery of the giant magnetoresistance（GMR）effect led to the new read-out technology of magnetic hard disk.However,with the development of advanced magnetic media and technology,the era of GMR has only lasted about ten years.The subsequent development is magnetic tunnel junction devices because the tunneling magnetoresistance effect can reach 1000%.As an important branch of condensed matter physics,spintronics has emerged and is of various intriguing physics phenomena.In the present thesis,we will launch following studies in the field of spintronics.1.Interfacial anomalous Hall effect of（001）orientated L1₀ ordered iron-platinum（Fe Pt）magnetic alloy films.To deeply understand the mechanism of the anomalous Hall effect in magnetic materials,we selected DC magnetron sputtering-grown L1₀ phase single crystal iron-platinum（Fe Pt）films with（001）orientation and perpendicular magnetic anisotropy and measured the transverse and longitudinal resistivities by the four-probe electrical measurement method.By analyzing the temperature-dependent anomalous Hall effect,the relationship between anomalous Hall resistivity and longitudinal resistivity can be well described by the scaling lawρ_AH=aρ_xx+bρxx².The anomalous Hall parameters a and b have linear relation with the reciprocal of thickness（1/d）.Their intercept and slope correspond to the bulk and the interfacial contributions,respectively.We measured iron-palladium（Fe Pd）alloys in the L1₀ phase and found similar phenomena.In conclusion,we verify the existence of interfacial anomalous Hall effect caused by interfacial symmetry breaking.2.Modification of magnetic damping parameter in cobalt-nickel（Co Ni）magnetic alloys by the band filling effect.Effectively reducing the damping parameter is very important to reduce the energy loss of spintronic devices.To investigate the mechanism of intrinsic damping,we grew high-quality epitaxial films of Co_1-xNi_x disordered alloys on STO（001）substrates.Because Co and Ni metals have different numbers of 3d electrons,the density of states of Co Ni near the Fermi level can be continuously and effectively regulated by changing the alloy composition.We calculated the electronic structure by density functional theory（DFT）and measured the magnetic damping parameter by time resolved magneto-optical Kerr effect（TRMOKE）.The magnetic damping parameter and the density of state near the Fermi level exhibit similar trends as a function of the alloy composition.We experimentally and theoretically prove that the damping parameter can be effectively reduced by the band filling effect,which is beneficial to the application and development of spintronic devices.3.Control of the spin chirality in non-collinear antiferromagnetic Mn₃Sn alloys by interface Dzyaloshinskii-Moriya interaction（DMI）.Chiral materials have the characteristics of lower energy consumption and higher efficiency.The study of chiral spintronics has been focused on ferromagnetic materials.Compared with ferromagnetic materials,antiferromagnet（AFM）have the characteristics of fast switching speed and great stabilization,so it is very important to study the spin chirality of non-collinear AFM.The spin chirality of noncollinear AFM depends not only on its physical properties,but also on the interfacial DMI of the surface/interface.Hence,we study anomalous Hall effect in non-collinear antiferromagnetic Mn₃Sn（11-20）epitaxial films and Mn₃Sn/Pt bilayer films.When the thickness d of Mn₃Sn in Mn₃Sn（d）/Pt decreases,the anomalous Hall resistivity changes from negative to positive.Alternatively,we performed temperature-dependent measurements on Mn₃Sn（10 nm）/Pt.It is found that when the temperature becomes lower,the anomalous Hall resistivity also changes from positive to negative.It has been shown theoretically that the sign of the anomalous Hall conductivity in noncollinear AFM is determined by the sign of the spin chirality.The existing theoretical studies have shown that the sign of anomalous Hall conductivity is determined by the sign of the spin chirality of the noncolinear antiferromagnets.Thereby,the aforementioned results of our experiments indicate that the interfacial DMI and Mn₃Sn render opposite sign of spin chirality,and compete with each other.Due to the decreasing thermal fluctuation of spin,the interfacial DMI becomes larger at low temperature,thus the spin chirality and anomalous Hall resistivity change signs.Similarly,when the DMI becomes larger because of thinner Mn₃Sn film,the spin chirality and anomalous Hall resistivity also change their signs.4.Electric field modification of magnetic topological insulators.The surface states of topological insulators are the keystone of improving the efficiency of spin-charge conversion.As an important physical phenomenon,weak localization occurs at low temperatures in electronically disordered systems,in which coherent backscattering of weakly localization electrons and weak anti-localization caused by spin-orbit coupling（SOC）both lead to negative（positive）quantum correction of conductivity（resistivity）.Therefore,Rashba SOC coefficient can be obtained by analyzing magnetoresistance curve at low temperatures.Hence,it is expected to obtain Rashba SOC coefficient by measuring magnetoresistance at low temperatures of Cr-doped(Bi_1-xSb_x)₂Te₃（0001）,a typical topological insulator.We performed low-temperature measurements of magnetoresistance and found weak-localization effect.The measurement results were analyzed using Iordanskii-Lyanda-Geller-Pikus（ILP）model to obtain the spin scattering time generated by the Rashba SOC.Experiments have shown an inverse proportional relationship between spin scattering time and electron scattering time,and Dyakonov-Perel（DP）spin scattering plays a dominant role,which can be attributed to the Rashba effect.As the ionic liquid electric field increases,the Rashba coefficient increases first and then decreases with the electric field.The Rashba coefficient is effectively increased by a factor of 30%by the electric field,which is conducive to improve the efficiency of the spin-charge conversion in the topological materials and the development of the spintronic device of the topological materials.