| Spin dynamics refers to the dynamic response of magnetization after external excitations, such as microwave, light, current, etc. The microwave excited spin dynamics begins from the frontier research on ferromagnetic resonance (FMR) of bulk magnetic materials in1940s, and it moves to the low dimentional magnetic structures as they can be created by the modern micro-nanofabrication and thin film growth techniques. Spintronics, which involves the study of active control and manipulation of spin degrees of freedom in solid-state systems, especially in low dimentioanl magnetic structures, is an important branch of condensed matter physcis today. The combination of spin dynamics and spintronics in low dimentional magnetic structures has opened up new world of these two disciplines.Spin dynamics move to low dimentional magnetic structures, and combine with spintronics, new instruments should be developed to fulfill the special need. In this thesis, we first introduce the home established broadband FMR system; Then we study the spin dynamics of low dimentional magnetic structures (magnetic thin films, magnetic micro-nano disks) with the system; At last, on the discipline which spin dynamics and spintronics combined, we develop a method to quantify spin Hall angle.(1) Based on vector network analyzer (VNA) and coplanar waveguide (CPW) structure, we establish a broadband FMR system. VNA serves as microwave source and feeds into CPW which generates a microwave filed acting on the low dimensional magnetic sample; A rotary electromagnet supply bias magnetic field, the field direction can be rotated in the plane; VNA detects the absorption of microwave when the magnetic samples are on the resonance condition; Home writed LabVIEW programs in computer control the whole system, collect and process data automatically. VNA can output microwave with a fixed frequency, and microwave frequency can also be sweeped. Then this system can achieve FMR measurement in sweeping frequency mode in addition to the conventional sweeping magnetic field mode.We design and fabricate several CPW fixtures to fulfill different needs and extend functionality.(2) Utilizing the broadband FMR system, we measure the uniform FMR resonance mode of cobalt polycrystalline film. We obtain the g factor by fitting the relationship of resonance frequency and resonace field according to the Kittel equation; By fitting the angular dependent of resonance frequency or magnetic field, the magnetirc anisotropy and effective magnetization are obtained; By linearly fitting the linewidth as a fuction of microwave frequency, the intrinsic Gilbert damping factor is determined.(3) Utilizing the broadband FMR system, we measure the magnetic vortex resonance of FeNi micro disks which means the system has the ability to measure micro-nano magnetic structures.The disks are fabricated on the signal line of a shorted CPW, and the magnetic vortex resonance absorption is observed by the reflection coefficient.And we find that the vortex resonance frequency is proportional to the disk’s aspect ratio.(4) Utilizing the broadband FMR system with added transport measurements functionality, we develop a method to quantify spin Hall angle (SHA). The method combines the spin pumping and inverse spin Hall effect (ISHE), and utilizes the microwave photoresistance. With this method we separate the inverse spin Hall effect from other unwanted effects for FeNi/Pt bilayers using out-of-plane microwave excitation. Through microwave photoresistance measurements, the in-and out-of-plane precessing angles of the magnetization are determined and enabled for the exact determination of the injected pure spin current. This method is demonstrated with an almost perfect Lorentz line shape for the obtained ISHE signal and the frequency independent SHA value as predicted by theory. By varying the Pt thickness, the SHA and spin-diffusion length of Pt is quantified as0.012±0.002and8.3±0.9nm, respectively. |
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