| Microwave magnetic materials can be used as electromagnetic shielding materials and radar absorbing materials and also can be applied in many kinds of microwave devices. According to application background, various demands have been made to the microwave magnetic properties, driving the related fundamental theoretical researches. The central issue in the microwave magnetic resonance research is that the quantitative relationship between the static and dynamic magnetic parameters is derived according to the physical model of magnetic resonance, which can be built combining the structure and performance of material. This provides an important theoretical guiding in analysis and designs of microwave magnetic materials.The shapes and sizes of materials greatly affect the microwave magnetic spectra. When calculating the effective electromagnetic parameters of composites consisting of magnetic powders with shape anisotropy, we need to consider the influences of shape and orientation of particles on the expression of the intrinsic permeability and effective medium formula. However, the existing calculation method is a little complicated, which is not suitable to provide the guidance for the material design. When the size is minished to nano level, multi-resonance behaviors can be observed. The classical resonance models on the bulk materials cannot interpret this phenomenon. The spin wave theory(exchange resonance model) fills that gap. But so far the research on the effect of dipolar interaction on the microwave magnetic spectra is relatively weak. Moreover, this thesis first illustrates that multi-resonance absorbance peaks still can be excited for the self-assembled micron scale ferromagnetic particles containing nanostructures unit, which are synthesized via hydrothermal route. It is necessary to deserve further investigation combining the existing theory.The damping is an important nondimensional parameter of influencing the characteristic of microwave magnetic resonance spectra. The further development of spintronics closely related to the FMR of magnetic films demands the films that have a thickness in the nanometer range and at the same time exhibit low damping. The intrinsic damping constant of yttrium iron garnet(Y3Fe5O12, YIG) ferrite material is one of the smallest in all magnetic materials. If the YIG nano films with low damping can be grown by sputtering, it is of great practical significance to realize the commercialization application of YIG-based spintronic devices.Aims at the above-mentioned problems, the detailed elucidations have been put forward in this thesis. This research mainly consists of the following four parts:1. The research on the effect of relevant parameters on the microwave complex permeability of thin films and composites consisting of powders.(1) The expressions of magnetic spectra and resonance of thin films are deduced according to the angle relationships between external magnetic field and anisotropy field(except the demagnetizing field).(2) The physical model of magnetic structure is created according to the orientation condition of nanometer thick ferromagnetic flakes in the matrix, and thus a more simple expression of intrinsic permeability is deduced via the double coordinate system combining the Gilbert equation. This can provid convenient channel for the microwave permeability calculation of nano-structured magnetic particles(3) Combined with modified Maxwell-Garnett mixing rule, the simulating calculation of magntic spectra of composites can be performed. The relationships between microwave permeability and relevant variables can be reflected directly, which are validated by the experiment results. These results offer the theoretical foundation for guiding design of high frequency magnetic materials.2. The complementary research on microwave multi-resonance characteristics of nano-sized magnetic powders and films.(1) Multiple resonance mechanisms of nano-scale magnetic powders and films are summarized firstly. The nano Fe have been uniformly dispersed in the paraffin by use of mechanical agitation so as to enable the accurate analysises of mutli-resonance magnetic spectra of nanocomposites.(2) The magnetic dipole interaction between nanoparticles is firstly introduced for the comprehensive investigation and analysis of dynamic magnetism characteristic in centimeter wave(0.5GHz-18GHz) and millimeter wave band(26GHz-40GHz), which further improve the resonance mechanism of nano-magnetic structure.(3) The experimental studies are found that a mixture in proper proportions of micron and nano scale Fe will be helpful to get larger complex permeability due to the enhanced magnetic dipole interaction at 0.5GHz to 2GHz, which provide a new idea for the solution of bottleneck problem for microwave absorbing in low frequency range.3. The study on multi-resonance mechanism of micron-scale ferromagnetic metal powders containing nanostructures units.(1) Several kinds of self-assembled ferromagnetic metal particles in the scale of micron meters are synthesized by the hydrothermal method. The results show that multi-resonance peaks also can be excited. The exchange resonance associated with nanostructure can be tentatively applied to explain multi-resonance mechanism, which enrichs the research contents about resonance model of non-uniform procession.(2) The expression of multi-resonance magnetic spectrum for Ni nanobelt composites is derived based on a linear superposition of several overlapped resonance curves combing Gilbert Equation. A good agreement is achieved between the fitted and experimental results,which proves the rationality of this theoretical calculation method.4. The study of the microwave ferromagnetic resonance characteristics and the relevant spintronic effects of low damping YIG nano-film by AC magnetron sputtering.(1) The YIG films with low damping are successfully grown on GGG substrates by optimizing processing conditions. The film has a FMR linewidth comparable to that of YIG film deposited by commonly used PLD technique. Besides, the reproducibilities and homogeneities of the film are higher than those of the PLD film. The relatively high-quality YIG nanofilm is grown on the HEAN-Cu-HEAN(HCH) metallic bottom electrode. This will lay the foundation for the future comericial YIG-based microwave devices with low loss.(2) When the YIG nanofilm is prepared at a substrate temperature of 750 oC and an Ar flow rate of 16 sccm, some raised grains will exist on the surface. The surface roughness becomes larger, which can lead to the excitation of two-magnon scattering. This not only expands the FMR linewidth, but has an adverse effect on the spintronic effect associated with interface state.(3) The measurement results of Inverse Spin Hall Effect(ISHE) voltage signals from the YIG/Pt sample show that the ISHE voltage was distinct higher than that of PLD films, which will contribute to promoting in-depth study of YIG-based spintroinc. Besides, the measured damping constant of YIG/Pt sample is substantially larger than expected according to conventional spin pumping theory, which confirms the existence of magnetic proximity effect(MPE) from the other side. |
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