High Frequency Properties Of Ferromagnetic Metallic Thin Films

This thesis describes a series of experiments and theories aimed at the high frequency properties of magnetic material which has been a bottleneck in the move towards integration of monolithic applied in higher frequency. Base on the spin precession which is fundamental in high frequency magnetization behavior, the underlying mechanism of magnetic material with higher permeability and resonance frequency, the methods to accurate determine the magnetic anisotropy field, and the technique to in-situ control over the high frequency performance of magnetic thin films were investigated. On the other hand, understanding and control of the interplay between charge, spin, and magnetization dynamics in ferromagnetic materials is required for further development of spintronic device. In addition to using spin rectification effect to realize DC electrical detection of spin dynamics, we were able to develop new microwave measurement techniques.The major results of this thesis are as follows:1 With an effective bianisotropy picture, the Snoek's limit, planar ferrite formula, and Acher's limit which are current three models to describe the high frequency properties of magnetic materials, can be reconciled. A prolate elliptical precession of the magnetization about its equilibrium direction is the key point to obtain higher permeability at higher frequencies.2 Rotational magnetization curves are used to investigate accurately the anisotropy and the rotational magnetization process of uniaxial magnets. This method utilizes an angular measurement of magnetization as a function of angle between the magnetic field and the reference axis. The information about anisotropy, such as the directions of easy axis and hard axis, as well as the anisotropy field are acquired. Simultaneously, the rotational magnetization reversal processes are derived.3 New technique to in-situ control over the micro-anisotropy of magnetic thin films is developed. The dipolar interaction caused by the striped pattern of the two phases is identified as the origin of the in-plane magnetic anisotropy. Therefore the high frequency properties of magnetic thin films can be in-situ manipulated in a large range by utilizing oblique deposition.4 Realized in DC electrical detection of spin dynamics due to spin rectification effect. This method is introduced in studying the spin precession in Permalloy microstrips. The nature of microwave assisted magnetization switching is proved as a static embodiment of the dynamic response of the magnetization excited by microwave. In addition, the influence of foldover effect and nonlinear damping on the spin precession cone angle is systematically studied.5 A spintronic approach is introduced to transform classic Michelson interferometry that probes electromagnetic phase only. This method utilizes a nonlinear four-wave coherent mixing effect. Its physical principle described by an analytical model is in excellent agreement with experiments. Spintronic Michelson interferometry allows direct probing both spin resonance phase and the relative phase of electromagnetic waves via microspintronics. Thereby, it breaks new ground for cross-disciplinary applications with unprecedented capabilities, which we demonstrate via a powerful phase-resolved spin resonance spectroscopy on magnetic materials.