Research On Heavy Metal/Magnetic Insulator Spin Heterostructure Materials And Its Effects

With the guidance of morden microeletronic technology,the current integrated circuit technology is developing rapidly and also faced with the inevitable problems like local heating caused by excessive integration of electronic components.Spintronic takes advantage of the spin freedom of electrons,which has become the basis for the construction of the new generation of spintronic devices with high density and low power consumption.The generation,transmission and detection of spin current are the topics of spintronics.In this dissertation,the spin pumping effect,spin transportation and inverse spin Hall effect in yttrium iron garnet(YIG)/metal heterostructure were investigated based on the single-crystal YIG thin films prepared by liquid phase epitaxial method.We found the spin pumping effect in the YIG magnetic heterostructure system,and revealed the spin transmission characteristics in YIG/barrier/Pt structure.A new type of spin detection material with large spin Hall angle was developed.In view of the above research topics,the main study contents of this dissertation include:1)The giant damping enhancement effect due to the exchange coupling in YIG/Co₂Fe Al_0.5Si_0.5(CFAS)magnetic heterostructure was studied,which expanded the application scope of spin pumping effect.The CFAS film is a magnetic material with high spin polarizability.In the ferromagnetic resonance(FMR)test of YIG/CFAS magnetic heterostructure,we found the giant damping enhancement and FMR field shift.We employed a Cu spacer to isolate the exchange coupling between the two magnetic layers,due to the weak spin-orbit coupling and long spin diffusion length of Cu.Through the study of the static and dynamic magnetic properties of the heterostructure,we have the following findings:1.The Cu spacer isolates the exchange coupling between the magnetic layers,which was revealed by the static and dynamic magnetic tests.2.The damping enhancement came from two sources:spin current injection caused by spin pumping at the interface region and exchange coupling between the magnetic layers.3.The damping variation in the magnetic heterostructure is related to the thickness of the CFAS layers.With the change of the CFAS thickness,it firstly increases,then decreases and finally saturates.Our findings demonstrate that spin pumping does not occur only in magnetic/non-magnetic heterostructures,and that there are limitations in measuring the efficiency of spin injection at the interface in terms of the variation of damping constants.2)Low spin injection efficiency is the main factor limiting the application of spintronics devices.The interface between ferromagnetic(FM)and nonmagnetic metal(NM)plays a fundamental role in the generation,transmission,detection of spin current,and spin-based devices.In this dissertation,we investigated the effect of the interfacial chemical states in spin injection efficiency.The interfacial structures and chemical states were analyzed by TEM,Raman,and XPS measurements.By different chemical treatments of YIG surface before the deposition of Pt layer,the chemical state of iron at the interface was controlled,and the efficiency of spin injection was significantly improved.In addition,it was found that argon ion bombardment,a key technique used in the fabrication of integrated devices,can significantly inhibit the interface spin injection.Based on the above studies on the chemical states of the interface,we propose a chemical method that can effectively recover the interfacial spin injection.This discovery has potential implications for spin generation,detection,and even optimization of spintronic devices.3)The interfacial spin injection efficiency can also be improved by inserting a barrier layer between the FM and NM layers.The main challenges in developing modern semiconductor spintronics is the efficiency of spin injection into semiconductor materials.How to efficiently inject spin current into semiconductor materials and the transmission characteristics of spin current within semiconductor materials have always attract much attention.We fabricated and studied the spin current injection efficiency in YIG/Ge Bi/Pt heterostructures and the spin current transport characteristics within the Ge Bi semiconductor barrier.We adjusted the band gap width of Ge Bi semiconductor,by changing the doping amount of bismuth atom.The spin pumping and inverse spin Hall effect were measured using ferromagnetic resonance system and our self-built system.We investigate the band-gap modulated in injection efficiency and spin current transmission characteristics,and achieve efficient spin injection in YIG/Ge Bi/Pt heterostructures.4)The spin Hall angle(?_SH)is an intrinsic property of spin detection materials which measures the efficiency of converting charge current into spin current and vice-versa.In order to meet the demand of spintronics devices for large spin Hall angle materials,we fabricated a new spin detection material Pt Sn alloy.The spin Hall Angle of Pt Sn alloy increased by two times compared with that of undoped pure Pt films.We studied the spin pumping effect of YIG/Pt Sn heterojunction with the help of ferromagnetic resonance system and calculated the interface spin mixing conductance.Then,the inverse spin Hall test system was built to test the thickness related inverse spin Hall voltage of Pt Sn films,and the spin diffusion length and spin Hall angle of Pt Sn alloy were extracted.Moreover,we calibrated the spin diffusion length and spin hall angle for pure Pt under the same experimental conditions in order to ensure the reliability of the data.The results obtained were consistent with the reports in other papers.The optimal atomic ratio of Pt and Sn was determined by changing the doping concentration of Sn.The spin Hall angle is 0.055 for Pt and 0.089 for Pt_0.77Sn_0.23.Not only the Pt Sn alloy itself have great application value,but also the method of selecting appropriate atoms to doping into the metals with large spin Hall angle also has potential implications for developing materials with large spin Hall angle.