纳米铁磁金属粉体及铁氧体薄膜微波磁共振特性研究

发布时间：2019-07-01 12:44

【摘要】：微波磁性材料可以用作屏蔽材料、雷达吸波材料以及整合到多种高频微波器件中,根据应用背景,对微波磁性能提出了各种要求,进而推动了相关基础理论研究。微波磁共振研究的核心内容是结合材料的结构、性能,构建磁共振物理模型,推导材料的静态与动态磁性参数间的定量关系,从而为微波磁性材料的分析和设计提供理论指导。材料的形状和尺寸对微波磁谱有着重要的影响。当理论推导形状各向异性磁性粉体复合物的等效电磁参数时,需要考虑颗粒的的形状及取向情况对本征磁导率表达式以及有效媒质公式的影响。但是现有的计算方法过于复杂,不利于指导材料设计。当材料尺寸降到纳米量级时,通常呈现出多共振吸收峰,此时传统块材的共振模型将无法予以解释,自旋波理论(交换共振模式)填补了这一空白。但是到目前为止,有关纳米铁磁颗粒间的磁偶极相互作用对微波共振磁谱的影响研究相对比较薄弱。此外,本文首次发现采用水热合成技术制备的纳米自组装结构的微米尺度铁磁金属粉体同样可以激发出多共振吸收峰,有必要结合现有理论进行更深入的分析。阻尼因子是影响微波共振磁谱特性的一个重要无量纲系数。随着与磁性薄膜铁磁共振密切相关的自旋电子学的深入研究,要求薄膜在纳米厚度的同时保证有足够小的阻尼因子。钇铁石榴石(YIG)铁氧体是目前已知所有磁性材料中阻尼系数最小的材料之一,如果通过磁控溅射成功制备出具有低阻尼系数的纳米YIG薄膜,对实现基于YIG薄膜的自旋电子器件的商业化应用具有重要的现实意义。本文正是针对上述问题,进行相应的阐述。主要研究工作分为如下四个部分:1.各相关参变量对薄膜及粉体复合材料微波磁谱的影响研究。(1)根据外加静磁场,微波场与各向异性场(不含退磁场)之间的角度关系,推导薄膜磁性材料的磁谱及磁共振表达式。(2)根据片状铁磁颗粒在基体中的取向情况,构建磁结构物理模型。结合吉尔伯特方程,采用双坐标系的处理方法,推导出更加简洁的本征磁谱表达式,进而为纳米铁磁颗粒的微波磁谱计算提供了简便的渠道。(3)结合修正后的Maxwell-Garnett有效媒质公式进行复合物微波磁谱的仿真计算,直观反映出微波磁导率与参变量间的相互关系,并得到实验验证,为高频磁性材料的设计提供更准确的理论依据。2.纳米尺度粉体及薄膜磁性材料的微波多共振特性补充研究。(1)首先概述了纳米磁性粉体与薄膜的多共振机理。通过机械搅拌的方式成功实现了纳米尺度铁(Fe)粉在粘结剂石蜡中高度均匀的混合,为准确分析纳米复合材料的微波多共振磁谱特性提供了可能。(2)首次引入纳米颗粒间的磁偶极相互作用分析研究纳米尺度Fe粉在厘米波段(0.5GHz-18GHz)和毫米波段(26GHz-40GHz)的动态磁化行为,进一步完善了纳米磁结构的共振机制。(3)实验发现在微米尺度Fe中添加适当比例的纳米Fe,在增强的磁偶极相互作用下,有助于提高在较低频段(0.5GHz-2GHz)的磁导率,这为解决电磁波在低频段的吸收瓶颈问题提供了一种思路。3.含有纳米结构单元的微米尺度铁磁金属粉体的多共振机制研究。(1)采用水热合成方式制备了多种纳米自组装结构的微米尺度铁磁金属粉体,它们在微波频段都激发出了多共振吸收峰。本文探索性将交换共振模式移植到纳米结构单元,丰富了非一致进动共振模式的研究内容。(2)结合吉尔伯特方程,采用多共振峰叠加的思路推导了Ni纳米薄带粉体多共振模式下的磁谱表达式,理论值与实验结果比较吻合,证实了这一理论计算方法的合理性。4.磁控溅射沉积低阻尼YIG铁氧体纳米薄膜的微波铁磁共振特性及与其相关的自旋电子效应研究。(1)通过优化磁控溅射的沉积工艺条件,在Gd3Ga5O12(GGG)衬底上制备了低阻尼系数的YIG纳米薄膜。与目前普遍采用的脉冲激光沉积(PLD)工艺相比,不仅具有相当的FMR线宽,而且薄膜的均匀性和结果的可重复性都要优于PLD薄膜。与此同时,尝试了在金属底电极HEAN-Cu-HEAN(HCH)上沉积相对高质量的YIG纳米薄膜,为实现将YIG薄膜用于商业低损耗微波单片集成器件中奠定了基础。(2)在较高Ar气流速(16sccm)及高温沉积(750oC)条件下,YIG纳米薄膜表面存在大量突起的晶粒,导致表面粗糙度变大,产生双磁散射过程。这不仅扩展了FMR线宽,而且对依赖于界面条件的自旋电子效应也产生不利影响。(3)YIG/Pt结构的逆自旋霍尔效应(ISHE)电压的测量结果表明:与采用PLD工艺制备的YIG/Pt相比,ISHE电压信号有显著提升,促进了基于YIG自旋电子学的深入研究。此外,测试发现基于自旋泵效应而提高的阻尼系数要低于实验测量结果,从另一侧面证实了近邻磁化效应(MPE)的存在。
[Abstract]:The microwave magnetic material can be used as a shielding material, a radar wave-absorbing material and a whole-in-to-many high-frequency microwave devices. The core content of the microwave magnetic resonance study is to combine the structure and performance of the material, to construct the magnetic resonance physical model, to derive the quantitative relation between the static and dynamic magnetic parameters of the material, so as to provide the theoretical guidance for the analysis and design of the microwave magnetic material. The shape and size of the material have an important influence on the microwave magnetic spectrum. When the equivalent electromagnetic parameters of the anisotropic magnetic powder composites are derived theoretically, the influence of the shape and orientation of the particles on the intrinsic permeability and the effective medium formula needs to be taken into account. However, the existing calculation method is too complicated to guide the material design. When the size of the material drops to the nanometer level, a multi-resonance absorption peak is usually present, at which time the resonance model of the conventional block will not be explained, and the spin-wave theory (switched resonance mode) fills this gap. So far, the influence of the magnetic dipole interaction between the nano-ferromagnetic particles on the microwave resonance magnetic spectrum is relatively weak. In addition, this paper first finds that the nano-scale ferromagnetic metal powder prepared by the hydrothermal synthesis technology can also excite the multi-resonance absorption peak, and it is necessary to carry out more in-depth analysis in combination with the existing theory. The damping factor is an important dimensionless factor that affects the properties of the microwave resonant magnetic spectrum. With the in-depth study of the spin electronics, which is closely related to the magnetic resonance of the magnetic thin film, the film is required to have a sufficiently small damping factor at the same time as the nano-thickness. The iron garnet (YIG) ferrite is one of the materials currently known to have the least damping coefficient in all the magnetic materials, and if the nano-YIG film with the low damping coefficient is successfully prepared by magnetron sputtering, It is of great practical significance to realize the commercial application of the spin electronic device based on the YIG film. In this paper, the above-mentioned problems are set forth in this paper. The main research work is divided into four parts:1. The influence of each related parameter on the microwave magnetic spectrum of the thin film and the powder composite was studied. (1) according to the angle relation between the applied static magnetic field, the microwave field and the anisotropic field (excluding the demagnetizing field), the magnetic spectrum and the magnetic resonance expression of the thin-film magnetic material are deduced. And (2) constructing a magnetic structure physical model according to the orientation of the flaky ferromagnetic particles in the matrix. In combination with the Gilbert's equation, a more concise intrinsic magnetic spectrum expression is derived by using a two-coordinate system, and a simple channel is provided for the calculation of the microwave magnetic spectrum of the nano-ferromagnetic particles. And (3) combining the modified Maxwell-Garnett effective medium formula to carry out the simulation calculation of the complex microwave magnetic spectrum, and the mutual relation between the microwave permeability and the parametric variable is directly reflected, and the experimental verification is obtained, so that a more accurate theoretical foundation is provided for the design of the high-frequency magnetic material. Study on microwave multi-resonance characteristics of nano-scale powder and thin-film magnetic material. (1) The multi-resonant mechanism of the nano-magnetic powder and the thin film is introduced first. By means of mechanical stirring, the highly uniform mixing of the nano-scale iron (Fe) powder in the binder paraffin is realized, and it is possible to accurately analyze the properties of the microwave multi-resonant magnetic spectrum of the nanocomposite. (2) The dynamic magnetization behavior of the nano-scale Fe powder in the centimeter wave band (0.5 GHz to 18 GHz) and the millimeter wave band (26 GHz to 40 GHz) is studied by the magnetic dipole interaction analysis between the nano-particles for the first time, and the resonance mechanism of the nano-magnetic structure is further improved. (3) The experiment shows that the proper proportion of the nano-Fe is added to the micro-scale Fe, and the magnetic permeability of the lower-frequency section (0.5 GHz-2 GHz) can be improved under the enhanced magnetic dipole interaction, which provides a thought for solving the problem of the absorption bottleneck of the electromagnetic wave in the low-frequency section. Multi-resonant mechanism of micro-scale ferromagnetic metal powders containing nano-structural units. (1) The micro-scale ferromagnetic metal powder with various self-assembled structures is prepared by hydrothermal synthesis, and the multi-resonance absorption peak is excited in the microwave frequency band. In this paper, the exchange resonance mode is transferred to the nano-structure unit, and the research content of the non-uniform precession resonance mode is enriched. (2) In combination with the Gilbert equation, the magnetic spectrum expression in the multi-resonant mode of the Ni-nano-thin-band powder is derived by using the method of superposition of the multi-resonance peaks, and the theoretical value is in good agreement with the experimental results, and the rationality of the theoretical calculation method is proved. Magnetic resonance and spin-electron effect of a low-damping YIG ferrite nano-film deposited by magnetron sputtering. (1) a YIG nano-film with low damping coefficient is prepared on a Gd3Ga5O12 (GGG) substrate by optimizing the deposition process conditions of the magnetron sputtering. Compared with the currently used pulse laser deposition (PLD) process, not only has the equivalent FMR line width, but also the uniformity of the film and the repeatability of the result are better than that of the PLD film. At the same time, a relatively high quality of YIG nano-film is deposited on the HEAN-Cu-HEAN (HCH) of the metal bottom electrode, which lays a foundation for realizing the use of the YIG thin film in a commercial low-loss microwave monolithic integrated device. (2) Under the condition of higher Ar gas flow rate (16 sccm) and high temperature deposition (750oC), the surface roughness of the YIG nano-film is increased and the double-magnetic scattering process is generated. This not only extends the FMR line width, but also has an adverse effect on the spin-electron effect depending on the interface conditions. (3) The measurement of the anti-spin Hall effect (ISHE) voltage of the YIG/ Pt structure shows that the ISHE voltage signal is obviously improved compared with the YIG/ Pt prepared by the PLD process, and the in-depth study based on the YIG spin electronics is promoted. In addition, the test shows that the damping coefficient, which is improved based on the spin-pump effect, is lower than the experimental measurement, and the existence of the neighbor magnetization effect (MPE) is confirmed from the other side.
【学位授予单位】：电子科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM27

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