Metallic ferromagnetic (FM) thin film heterostructures play an important role in emerging magnetoelectronic devices, which introduce the spin degree of freedom of electrons into conventional charge-based electronic devices. As the majority of magnetoelectronic devices operate in the GHz frequency range, it is critical to understand the high-frequency magnetization dynamics in these structures. In this thesis, we start with the static magnetic properties of FM thin films and their optimization via the field-sputtering process incorporating a specially designed in-situ electromagnet. We focus on the origins of anisotropy and hysteresis/coercivity in soft magnetic thin films, which are most relevant to magentic susceptibility and power dissipation in applications in the sub-GHz frequency regime, such as magnetic-core integrated inductors. Next we explore GHz magnetization dynamics in thin-film heterostructures, both in semi-infinite samples and confined geometries. All investigations are rooted in the Landau-Lifshitz-Gilbert (LLG) equation, the equation of motion for magnetization. The phenomenological Gilbert damping parameter in the LLG equation has been interpreted, since the 1970's, in terms of the electrical resistivity. We present the first interpretation of the size effect in Gilbert damping in single metallic FM films based on this electron theory of damping. The LLG equation is intrinsically nonlinear, which provides possibilities for rf signal processing. We analyze the frequency doubling effect at small-angle magnetization precession from the first-order expansion of the LLG equation, and demonstrate second harmonic generation from Ni81 Fe19 (Permalloy) thin film under ferromagnetic resonance (FMR), three orders of magnitude more efficient than in ferrites traditionally used in rf devices. Though the efficiency is less than in semiconductor devices, we provide field- and frequency-selectivity in the second harmonic generation. To address further the relationship between the rf excitation and the magnetization dynamics in systems with higher complexity, such as multilayered thin films consisting of nonmagnetic (NM) and FM layers, we employ the powerful time-resolved x-ray magnetic circular dichroism (TR-XMCD) spectroscopy. Soft x-rays have element-specific absorption, leading to layer-specific magnetization detection provided the FM layers have distinctive compositions. We discovered that in contrast to what has been routinely assumed, for layer thicknesses well below the skin depth of the EM wave, a significant phase difference exists between the rf magnetic fields H rf in different FM layers separated by a Cu spacer layer. We propose an analysis based on the distribution of the EM waves in the film stack and substrate to interpret this striking observation. For confined geometries with lateral dimensions in the sub-micron regime, there has been a critical absence of experimental techniques which can image small-amplitude dynamics of these structures. We extend the TR-XMCD technique to scanning transmission x-ray microscopy (STXM), to observe directly the local magnetization dynamics in nanoscale FM thin-film elements, demonstrated at picosecond temporal, 40 nm spatial and < 6° angular resolution. The experimental data are compared with our micromagnetic simulations based on the finite element analysis of the time-dependent LLG equation. We resolve standing spin wave modes in nanoscale Ni81 Fe19 thin film ellipses (1000 nm x 500 nm x 20 nm) with clear phase information to distinguish between degenerate eigenmodes with different symmetries for the first time. With the element-specific imaging capability of soft x-rays, spatial resolution up to 15 nm with improved optics, we see great potential for this technique to investigate functional devices with multiple FM layers, and provide insight into the studies of spin injection, manipulation and detection.
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机译：金属铁磁（FM）薄膜异质结构在新兴的磁电子器件中扮演着重要角色，该器件将电子的自旋自由度引入了传统的基于电荷的电子器件中。由于大多数磁电子设备都在GHz频率范围内工作，因此了解这些结构中的高频磁化动力学至关重要。在本文中，我们从调频薄膜的静态磁性能开始，并通过结合专门设计的原位电磁铁的场溅射工艺对其进行优化。我们关注于软磁薄膜中的各向异性和磁滞/矫顽力的起源，这些起源与在低于GHz频率范围的应用中的磁化率磁化率和功耗有关，例如磁芯集成电感器。接下来，我们探索薄膜无限结构中的GHz磁化动力学，包括半无限样本和有限几何形状。所有研究均基于Landau-Lifshitz-Gilbert（LLG）方程，即磁化运动方程。自1970年代以来，就用电阻率来解释LLG方程中的现象学吉尔伯特阻尼参数。我们基于这种阻尼电子理论，对单金属FM薄膜的吉尔伯特阻尼中的尺寸效应进行了首次解释。 LLG方程本质上是非线性的，这为射频信号处理提供了可能性。我们从LLG方程的一阶展开式分析了小角度磁化旋进时的倍频效应，并展示了在铁磁共振（FMR）下Ni81 Fe19（坡莫合金）薄膜产生的二次谐波，其效率比其高三个数量级。传统上用于射频设备的铁氧体中。尽管效率低于半导体器件，但我们在二次谐波产生中提供了场和频率选择性。为了进一步解决射频激励与复杂度更高的系统（例如由非磁性（NM）和FM层组成的多层薄膜）中的磁化动力学之间的关系，我们采用了功能强大的时间分辨X射线磁性圆二色性（TR- XMCD）光谱。软X射线具有特定于元素的吸收，只要FM层具有独特的成分，就可以进行特定于层的磁化检测。我们发现，与常规假设相反，对于远低于EM波趋肤深度的层厚度，在由Cu隔层分隔的不同FM层中，rf磁场H rf之间存在明显的相位差。我们提出了基于薄膜堆叠和基底中电磁波分布的分析，以解释这一惊人的发现。对于在亚微米范围内具有横向尺寸的局限性几何，已经严重缺乏能够对这些结构的小振幅动力学成像的实验技术。我们将TR-XMCD技术扩展到扫描透射X射线显微镜（STXM），以直接观察纳米级FM薄膜元件中的局部磁化动力学，在皮秒级时间，40 nm空间和<6°角分辨率下证明了这一点。基于对时间相关的LLG方程的有限元分析，将实验数据与我们的微磁仿真进行了比较。我们首次解析了纳米Ni81 Fe19薄膜椭圆形（1000 nm x 500 nm x 20 nm）中的自旋波模式，具有清晰的相位信息，从而首次区分了具有不同对称性的简并本征模式。借助软X射线的特定于元素的成像能力，具有改进的光学器件的高达15 nm的空间分辨率，我们看到了这项技术在研究具有多个FM层的功能性设备方面的巨大潜力，并为自旋注入，操纵研究提供了见识和检测。
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