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Browsing by Subject "ferromagnetic resonance"

Now showing 1 - 3 of 3
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    Electrical, Microwave, And Thermoelectric Studies Of Epitaxial Heusler Compound-Based Thin Films
    (2018-04) Peterson, Timothy
    This thesis presents studies of epitaxial thin film structures based on Heusler compound ferromagnets, with particular focus on the static and dynamic properties of these structures relevant for spintronic device applications. In Chapter 1, a brief motivation is followed by an introduction to the spin physics of itinerant electronic materials, providing the framework for understanding the results presented in the following chapters. In Chapter 2, demonstrations of spin-orbit torques in epitaxial Heusler/Pt bilayers are presented. After characterizing the behavior of the spin-orbit torques through second-harmonic magnetoresistance techniques, the behaviors of the torques as a function of temperature are used to study the influence of the magnetic proximity effect on the dampinglike and fieldlike torque contributions. It is found that the dampinglike torque is due to the platinum spin-Hall effect, and is not influenced by the magnetic proximity effect. Conversely, the fieldlike torque is likely due to the interface Rashba effect, and is suppressed by the presence of the magnetic proximity effect. In Chapter 3, measurements of ferromagnetic resonance linewidths are presented for Heusler compound thin films, which are used to study the damping mechanisms of magnetization dynamics. Both intrinsic and extrinsic damping mechanisms are found, the former described by Gilbert damping and the latter due to the presence of magnon-magnon scattering processes. The Gilbert damping in these epitaxial Heusler thin films is shown to be very low relative to typical metallic ferromagnets, on the order of 10^(-4)-10^(-3) when expressed as a dimensionless Gilbert damping constant. In addition, evidence of an anisotropic Gilbert damping constant is presented for epitaxial Co(2)FeSi thin films. A methodology considering extrinsic magnon-magnon scattering contributions to the resonance linewidth is presented, revealing the characteristic lengthscale of magnetic inhomogeneity in these films. Finally, in Chapter 4 a method to measure (magneto)thermoelectric coefficients in thin films is outlined, which uses all-lithographic patterning and thermometry. Initial results for the Seebeck and anomalous Nernst coefficients in Heusler compound thin films are presented, along with interpretation.
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    The Study of a Ferromagnetic Resonance Measurement System Characterizing Magnetic Nanowires
    (2019-03) Zhou, Wen
    This thesis discusses the characterization of ferromagnetic nanowires (MNWs) and their applications. Chapter 2 introduces the static and dynamic properties of the MNWs and provides an overview to the ferromagnetic resonance (FMR) measurement system. Chapter 3 focuses on the design of the measurement grounded coplanar waveguide (GCPW) circuit, along with the co-simulation of GCPW circuit and ferromagnetic nanowire array (MNWA). Chapter 4 describes the implementation of the VNA-FMR measurement system, including the frequency-sweep and the field-sweep approaches, and the optimization of measurement configurations. The applications of MNWs are demonstrated in two aspects, one in passive microwave device design and another in bio-labeling system design. Chapter 5 presents a MNWA based self-biased circulator at Ka band that has the potential for MMIC integration. Chapter 6 proposes a MNWs-based biolabeling system for multiple cancer cell type detection. An algorithm for multi-MNW type identification is discussed, and the development path from MNWAs to use as MNWs is explained.
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    Study of Nanowires for Microwave and Millimeter Wave Frequency Applications
    (2021-12) Zhang, Yali
    This dissertation discusses the application of nanowire (NW) technology applied in millimeter wave and sub-millimeter wave frequency bands. Both magnetic nanowires (MNWs) and copper (Cu) NWs are studied. MNW is proposed for use as bio-labels in nanomedicine application and as magnetic substrate in non-reciprocal design for communication application. To do that, the ferromagnetic resonance (FMR) technique is adopted for MNWs characterization. Cu NW is investigated for use as vertical interconnect in integrated circuit (IC) for wireless communication applications. A coplanar waveguide (CPW) with NW Cu vias design was proposed and studied.The theory and simulation model of MNWs and Cu NWs are first discussed to provide preliminary understanding of the FMR of MNWs and concepts of Cu NW-based vias (chapter 2). Then the MNWs are fully characterized in the DC field domain. The FMR characterization system and methods are developed. The factors that influence the FMR characterization are studied. A tri-labeling system is built based on nickel (Ni), cobalt (Co) and iron (Fe) MNWs. The MNWs in a bio-mimicking and biological media are characterized (chapter 3). Next, to use MNWs in non-reciprocal devices, three key parameters are defined, FMR frequencies, permeability, and linewidth. A complete characterization method is developed to acquire these three parameters accurately (chapter 4). Lastly, the Cu NWs vias in a CPW structure are designed, fabricated, and measured in three frequency bands 0.04-40 GHz, 0.01- 67 GHz and 0.01-110 GHz. The NW via loss is extracted and compared to other advanced via technologies. A comparison of NW and conventional via is also presented. (chapter 5). The outcome of different study investigated in this work show the promising potential of NWs as a favorable material for future biomedical and communication applications.