| With the rapid development of portable electronic devices,people's demand for the integration and miniaturization of microelectronic devices continues to increase.Moore's law based on the traditional CMOS process is approaching the limit,and the problem of quantum tunneling and high power consumption are gradually emerging.In recent years,the spin properties of electrons have become a new development direction to overcome this bottleneck.In the burgeoning field of spintronics,research on the generation,detection,regulation of spin currents,and spintronic devices represented by heterostructure of magnetic insulators has aroused strong interest from scholars.Pure spin current can be generated in ferromagnetic insulating materials,which transfer information by means of the spin angular momentum of the electrons.Since there is no net charge current,the power consumption of the device can be greatly reduced.However,the voltage signal measured by the spin electronic devices with magnetic/heavy metal heterostructure usually contains an abnormal Hall voltage component caused by the magnetic proximity effect at the interface,which makes it difficult to accurately measure the spin Hall voltage.Therefore,the influence of the magnetic proximity effect needs to be solved by using a buffer layer material.Compared with ferromagnetic material,anti-ferromagnetic materials have the ability to transport spin current without external magnetic properties,which are ideal materials for buffer layers.Moreover,the precession frequency of the anti-ferromagnetic materials'spin magnetic moment is higher,enabling faster information processing and communication in the 5G field and even the next-generation terahertz wave range.Therefore,in this paper,ferrimagnetic insulator material yttrium iron garnet?YIG?and anti-ferromagnetic material nickel oxide?NiO?,are grown and prepared by pulse laser deposition processes.The influence of valence of iron ions on the magnetic properties of YIG thin films was mainly studied.The spin transport characteristics of YIG/NiO heterojunctions were studied in combination with spin pumping,spin Hall and inverse spin Hall measurements.While solving the influence of the magnetic proximity effect,a spin scattering enhancement mechanism dominated by the interface roughness of the thin film was discovered,which is of great significance for achieving efficient spin current injection and developing high-sensitivity spin electronics devices.Firstly,from the perspective of the spatial energy of magnetic materials,this thesis analyzes the precession process of the magnetic moment in detail based on the theory of magnetization dynamics,and then derives the conditional equations required for ferromagnetic resonance to occur,which provides a theoretical basis for calculating the ferromagnetic resonance line width of YIG film and extracting effective damping coefficient.Subsequently,the process of spin current generation in ferromagnetic/nonmagnetic heterojunctions is explained based on the spin pumping effect,and based on the theory of the mutual conversion relationship between spin current and charge current,the principle of spin Hall effect and inverse spin Hall effect are derived.Secondly,YIG films with low damping and long spin transport distance were grown on the gallium garnet garnet substrate by a pulsed laser deposition process.In addition,the effects of deposition temperature,oxygen pressure and annealing conditions on the composition structure,micro-morphology,hysteresis loop,and ferromagnetic resonance line width of YIG films were deeply studied.It has been analyzed that the presence of excessive ferrous iron and impurities such as YFeO3 in the film will lead to the weakening of the magnetic properties and distortion of the ferromagnetic resonance spectrum of YIG films.A systematic study of the static magnetic properties and high-frequency spin dynamics of YIG films prepared under the optimal growth conditions was performed in experiments.Hysteresis loop results show that the coercivity of the YIG film is about 4 Oe,the saturation magnetization value is1755 Gs,the optimal ferromagnetic resonance line width obtained at a frequency of 7GHz is about 8.3 Oe,and the damping coefficient is about 5.7×10-4.Moreover,the measurement of magneto-optical Kerr effect was used to find the magneto-optical enhancement phenomenon in YIG/graphene/YIG structural materials.Otherwise,The group velocity,relaxation time,and attenuation length of the magnetostatic surface spin wave in YIG films were excited and detected using an antenna.Finally,based on the growth and characterization of the anti-ferromagnetic NiO film,a series of YIG/NiO heterostructure films were prepared by adjusting the thickness of the NiO layer.Hysteresis loops,ferromagnetic resonance,and spin pumping measurement results show that when the NiO layer is thick,the ferrimagnetic/anti-ferromagnetic exchange coupling can inhibit the transfer of spin angular momentum between the YIG/NiO interface.Subsequently,combined with the inverse spin Hall effect measurement and spin Hall magnetoresistive device,the transport characteristics of spin current in the YIG/NiO/Pt heterojunctions were studied.The experimental results show that the anti-ferromagnetic buffer layer NiO can effectively suppress the effect of the magnetic insulating layer YIG on the magnetization of the Pt atomic layer at the interface,thereby eliminating the influence of the abnormal Hall voltage component in the inverse spin Hall voltage measurement.Atomic force microscopy and spherical aberration corrected transmission electron microscopy measurements show that when the thickness of the NiO layer is about 1 nm,the interface between the NiO and Pt layer is rough and discontinuous growth.In the end,from the perspective of spin scattering dominated by interface roughness,this paper reasonably explains the deep-seated reasons for the enhancement of interface spin scattering on the inverse spin Hall voltage and spin Hall magnetoresistance. |
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