Study Of The Spin Current Transport And The Spin Dynamic Properties In Ferromagnet Heterostructures

With the electronic integrated functional devices going to ten nanometers scale, serious contradiction between the energy loss and the integration density is showing up. The electron spin can be used as an information carrier, which has low operation energy, high speed and novel quantum properties. It may bring a new generation of electronic information revolution. Electrical control of the spin dynamics and magnetization switching has been attracted the most concern in recent years. It is the only route to realize full-spin-current based spintronics functional devices and spin microwave devices. In this thesis, the spin current transport and the spin dynamics properties in magnetic heterostructures have been studied. First, magnetic insulator yittrium iron garnet(YIG) single crystal thin film was grown by using pulse laser deposition method and chemical metal organic decomposition method, respectively. Both the microstructures and the high frequency magnetic properties have been studied. The magnetic dynamics of the YIG/nonmagnetic heterostructures and the spin Hall magnetoresistance of the YIG/heavy-metal heterostructures were systematically investigated. Secondly, tuning of the magnetization dynamics and the interfacial spin pumping effect in nanometer ferromagnetic metal/nonmagnetic heterostructures have been studied based on the spin pumping theory and the long-range dynamic exchange coupling model. Finally, tailoring of the spin dynamics of the ferromagnetic/anti-ferromagnetic multilayer structures has been carried out. We designed and fabricated periodic exchange-biased stacks structures with tunable high frequency magnetization properties. The contents are divided into four parts shown as follows.1. High quality single crystal YIG thin films were grown by using pulse laser deposition method and chemical solution spin-coating method, respectively. The YIG thin films have excellent soft magnetic properties and high frequency magnetic properties. The effect of the thermal treatment on the spin pumping properties has been revealed in YIG/Au heterostructures. It was found that the Au surface morphology evolution had significant correlation with the spin pumping induced damping enhancement. The spin mixing conductance was obtained by using the spin pumping theory. The results may offer a new way to tailor the efficiency of spin pumping generated interfacial spin current in YIG/Au bilayers. Besides, we experimentally observed the linewidth broadening effect in YIG/Graphene heterostructure, whose spin mixing conductance as large as 2.45×1015 cm-2 was gained based on the spin pumping theory. The stress of the YIG/Graphene heterostructure was studied by measuring Raman spectra. It was found that YIG generated a compressive stress to the graphene layer which induced a red-shift of the 2D peak. The stress can split the Dirac point, and the spin-dependent energy band splitting will influence the spin current injection at the YIG/Graphene interface.2. The spin Hall magnetoresistance(MR) in YIG/(Pt, Pd) heterostructures has been investigated with an out-of-plane magnetic field. A novel interfacial spin current and spin accumulation valve effect has been proposed and observed in both YIG/Pt and YIG/Pd bilayers. Typical spin-valve-like MR curves were obtained by using planar Hall measurement. The results showed that the spin Hall MR switching field was significantly dependent on the current density. The spin-orbital effective field and torque theory were employed to explain the results. In order to exclude the proximity induced magnetization in Pt, we inserted 2 nm Cu to separate YIG and Pt. Spin-valve-like MR curves were gained in YIG/Cu/Pt system. An in-plane positive/negative bias field was used to investigate the spin Hall MR switching properties, which may be helpful to reveal the spin-orbital torque in YIG/heavy metal heterostructures.3. The effect of the heavy metal ruthenium(Ru) seed layer on the dynamic magnetic properties of the NiFe nanometer films has been studied by using FMR technique. We tuned the resonant field and damping constant in a large range by changing the thickness of Ru. With characterizing the microstructure and surface morphology, the relationship of the microstructure and the dynamic magnetic properties was revealed. The NiFe(111) orientation and large surface roughness will induce an inhomogenous anisotropy field. The damping enhancement originates from both the spin pumping and the two-magnon scattering process.4. The magnetization dynamics of the IrMn/Ru/NiFe/Ru/IrMn multilayers were studied based on the long-range dynamic exchange coupling model. It was found that both the Ru and IrMn thicknesses can greatly influence the resonant field. The static exchange bias effect was excluded by measuring the magnetization hysteresis loops and the angle dependent FMR. The results have large potential to be used in spin-current based microwave devices. Moreover, we experimentally observed an important permeability spectra modification effect of the half-pinned ferromagnetic layer in [NiFe/IrMn]N multilayers. By designing and fabricating different exchange bias stack structures, multi-resonant permeability spectra with wideband absorption linewidth were realized. The magnetization dynamics of the exchange-bias stack structure was analyzed by using the LLG equation. The resonant field, dynamic anisotropy field and damping constant of each stack were obtained. Our experimental theory and method can be used into the microwave circuit noise suppression area.