Browsing by Subject "Magnetics"

Now showing 1 - 5 of 5
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    AC Susceptibility and Anisotropic Magnetoresistance: A Study of Thin Magnetic Films
    (2019-12) Booth, Kevin
    The differential ac magnetic susceptibility of thin magnetic films was determined using the anisotropic magnetoresistance (AMR) to measure the response of the magnetization to an applied ac magnetic field. The ac susceptibility was measured as a function of an applied dc magnetic field. The frequency of the applied ac field was varied between 5Hz to 5000Hz. The ferromagnetic films investigated were permalloy, cobalt, nickel, and nickel with an antiferromagnetic nickel oxide layer on one surface. For all the samples investigated, the differential susceptibility magnitude was a function of the dc field magnitude and was frequency dependent, decreasing with increasing frequency.
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    Electrochemical Deposition of Magnetics Based Sensors
    (2019-12) Hein, Matthew
    Within the context of this thesis, advancements in sensor technology are driven in three separate applications. In each application electrochemistry is used as one of the primary fabrication steps, and magnetic phenomena are sensed in order to convey information about the different systems. The medical device industry is an area where various sensors are seeing increased use. Electromagnetic catheter tracking is an application that depends on high-quality magnetic sensors. The size of the sensor is a significant design constraint in catheters. Investigation of a microfabricated inductive sensor is pursued in chapter 4 of this thesis. High shape anisotropy inductive structures utilizing etched aluminum oxide as electroplating templates are investigated through first-order modeling and fabrication process development. Results show that the AAO is capable of producing high aspect ratio inductive structures though further development would be needed to achieve the consistency in etching required for large scale device fabrication. Biomimetic devices are another area of scientific interest where magnetics can play a role. Electroplated magnetic nanowires can act like large arrays of cilia. In chapter 5, biomimetic nanowire arrays are fabricated into microfluidic channels, and their movement sensed via a magnetic sensor. The nanowires provide a magnetic field that bends as fluid flows through the channel which enables a simple flow measurement through microfluidic channels. Similarly, a low frequency (>10Hz) vibration sensor is demonstrated utilizing a nanowire array above a magnetic sensor. Vibration of the sensor imparts momentum on the nanowires, which bend and leads to a time-varying field. In chapter 6, electrodeposition of Galfenol on a cylindrical surface is demonstrated for the first time. Galfenol has a large magnetostriction constant up to ~400 ppm. Utilizing a rotating cylinder electrode, the parameters to deposit Fe1-xGax films in the x = 15 to 35 range were found. The film's magnetostriction was then demonstrated as part of a torque sensor where magnetic anisotropy was controlled through texturing of the cylinder surface. The effect of magnetic shape anisotropy can be seen to play a significant role in the sensor's output by increasing the sensitivity of the sensor nearly 6x that of the non-textured film.
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    High Anisotropy Magnetic Materials for Data Storage and Spintronic Memory
    (2018-01) Quarterman, Patrick
    Data storage technologies that utilize magnetic materials for storage are key for both increasing areal density of storage in traditional hard disk media and providing low energy alternatives to traditional CMOS technology through spintronic memory and logic devices. Spintronic memory relies on the spin of an electron rather than charge and is a promising candidate for achieving non-volatility which can provide dramatic energy savings. A key challenge for magnetic based storage is achieving 10 nm or smaller feature sizes while retaining thermal stability. This requires development of magnetic thin films with large magnetocrystalline anisotropy. Switching the magnetization of high anisotropy magnetic materials requires large Oersted field or spin current. One way to decrease the switching energy is to lower the anisotropy during the switching process with an applied strain or heat. This scheme retains thermal stability during storage and makes write energies feasible from a technological aspect. Development of suitable high anisotropy materials at sub 10 nm scale has proved difficult due to limitations on traditional thin film growth methods, nanoscale effects, and additional requirements on materials for memory applications. The effect of a static strain on the magnetic anisotropy is well understood, but less so for application in devices which require fast switching and high cycling. The other approach to lowering switching energies is to use magnetic materials with small magnetization, such as Mn-based compounds. I will discuss my experiments to advance understanding of: development of FePt for HAMR media, effect of strain assisted switching on the spin state of FePt, and development of novel high anisotropy Mn-based materials with low magnetization. Finally, I will present my experimental realization of Ru as the 4th room temperature ferromagnetic element. Ru has been predicted to become ferromagnetic when placed into a metastable tetragonal or cubic phase. This new phase of Ru also has potential to achieve the requirements for a viable spintronic device. I will show my work on the realization of the tetragonal phase Ru using seed layer engineering in thin films, and its associated ferromagnetic properties.
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    Iron Nitride Based Magnetoresistance Devices For Spintronic Applications
    (2018-03) Li, Xuan
    The iron nitrides have been attracting a wide interest in spintronics researches due to their unique magnetic properties. In this thesis, I describe the experimental studies of the spintronic devices based on two important iron nitride materials, i.e. Fe16N2 and Fe4N. In the Fe16N2 based magnetoresistance device development, a heavy-metal free, low damping, and non-interface perpendicular current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) device with Fe16N2 magnetic layers has been demonstrated. The crystalline based perpendicular anisotropy of the Fe16N2 in the CPP GMR device is measured to be about 1.9 e7 erg/cm3, which is sufficient to maintain the thermal stability of the sub-10nm devices. The damping constant of the Fe16N2 thin film is determined to be 0.01 by a ferromagnetic resonance measurement, which is much lower than most existing materials with crystalline perpendicular magnetic anisotropy. The non-interface perpendicular anisotropy and low damping properties of make Fe16N2 a promising material for future spintronic applications. In the Fe4N material and device studies, both the (111) oriented and (001) oriented Fe4N thin films are prepared by optimizing the buffer layers, substrate temperatures and N:Fe composition. The most attractive properties of Fe4N in spintronics are the large spin asymmetric conductance and the negative spin polarization. The spin polarization of the (111) oriented Fe4N is investigated. The thickness dependence of the spin polarization of the (111) oriented Fe4N is also explored. Moreover, I have studied the Gilbert damping constant of the Fe4N (001) thin film by ferromagnetic resonance. The αFe4N is determined to be 0.021±0.02. Last but not least, the current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) device with Fe4N/Ag/Fe sandwich have also been fabricated and characterized. Giant inverse magnetoresistance is observed in the Fe4N based CPP GMR device, which confirms that the spin polarization of Fe4N and Fe4N/Ag interface is negative.
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    Spin transport and current induced magnetization dynamics in magnetic nanostructures.
    (2010-12) Chen, Xi
    The study of the interaction between conducting electrons and magnetization in a ferromagnet has stimulated much interest following the discovery of the giant magnetoresistive effect two decades ago. With the advance of fabrication techniques at the nanometer length scale, a variety of new magnetic nanostructures have emerged. These structures are interesting from both a scientific and technological perspective. Some of them have successfully led to applications in information storage industry. This thesis theoretically studies some of these structures and focuses on two aspects: (1) the effect of surface roughness in magnetoresistive devices, (2) spin transfer torque induced magnetization dynamics. Surface roughness is known to be an important source of scattering in small structures. We employ Landauer's formalism to study spin dependent electron transport in structures like spin valve, magnetic tunnel junction and nanowires. An efficient algorithm is developed to solve the scattering problem numerically. It is found that the resistivity and magnetoresistance are strongly influenced by the surface roughness scattering. The coupling between spin polarized current and local magnetic moment results in a torque on the magnetization. This induces dynamic effects such as magnetization reversal and switching. We propose an exchange coupled composite structure to study current induced reversal and show that this structure can significantly reduce the critical current. The spin torque can cancel the damping torque and induce steady precession. This type of spin torque oscillator is attractive as a microwave device at the nanoscale. Several of these oscillators can couple together and oscillate in a phase coherent manner. The mechanism for the coupling is studied analytically and using micromagnetic simulation. It is found that the coupling exhibits an oscillatory behavior through a spin wave mediated interaction.