Engineering Commons^™

Functional Properties Of Bulk And Meta-Material High Entropy Alloys, Cameron Jorgensen

Doctoral Dissertations

High Entropy Alloys (HEAs) are a class of material which is well-known for their high-temperature mechanical strength and corrosion resistance. In these materials, the entropy of mixing is used to encourage alloying between elements which are typically immiscible, sometimes described as alloying beyond the Hume-Rothery Rules. Specifically, the entropy of mixing is increased by including multiple elements on a single lattice site, increasing the free energy cost associated with phase separation. In the HEA community, this ‘high entropy effect’ is typically associated with alloy containing five or more elements. Achieving alloying between immiscible elements generally means the atomic size and/or …

Spin And Charge Transport In Metallic Ferrimagnets And Disordered Magnetic Oxides, Leopoldo A. Hernandez

Electronic Theses and Dissertations

Recent efforts have been exploring the use of thin film synthetic ferrimagnets and disordered magnetic oxides for applications in spintronic devices. Due to the antiferromagnetic exchange interaction, ferrimagnetic materials offer the ultrafast dynamics of the antiferromagnetic exchange, with a net magnetization that can be influenced externally. With two, or more, competing ferromagnet sublattices, interesting properties arise that depend on the final magnetic landscape after growth of the material and it’s inherent magnetic anisotropy energies. Properties such as magnetic compensation temperatures, and perpendicular magnetic anisotropy are attractive for applications in spintronic memory and logic devices, some already being implemented in MRAM …

Interfacial Magnetism And Anisotropy In Dirac And Weyl Semimetals, Noah Schulz

USF Tampa Graduate Theses and Dissertations

Semimetals have gained intense interest recently due to their exotic magnetic and electronic properties. One of the most widely studied semimetals is graphene, a Dirac semimetal. The utilization of graphene in devices and sensors requires interfacing it with other materials, which may induce potentially strong interfacial effects. Furthermore, graphene alone does not possess magnetic order. Studying the interfacial effects between graphene and magnetic materials is therefore of great importance in the application of graphene to meet modern technological needs. Furthermore, by understanding the fundamental interfacial physics between graphene and magnetic materials, new properties can be unlocked, broadening the possible applications …

Thermal, Magnetic, And Electrical Properties Of Thin Films And Nanostructures: From Magnetic Insulators To Organic Thermoelectrics, Michael J. M. Roos

Electronic Theses and Dissertations

Modern fabrication and growth techniques allow for the development of increasingly smaller and more complex solid state structures, the characterization of which require highly specialized measurement platforms. In this dissertation I present the development of techniques and instrumentation used in magnetic, thermal, and electrical property measurements of thin films and nanostructures. The understanding of trapped-flux induced artifacts in SQUID magnetometry of large paramagnetic substrates allows for the resolution of increasingly small moments. Using these methods, the antiferromagnetic coupling of the interface between a Y₃Fe₅O₁₂ film and Gd₃Ga₅O₁₂substrate is quantitatively …

Bioengineered Scaffolds To Induce Alignment And Promote Axon Regeneration Following Spinal Cord Injury, Kiet Anh Tran

Theses and Dissertations

Scaffolds delivered to injured spinal cords to stimulate axon connectivity often act as a bridge to stimulate regeneration at the injured area, but current approaches lack the permissiveness, topology and mechanics to mimic host tissue properties. This dissertation focuses on bioengineering scaffolds through the means of altering topology in injectables and tuning mechanics in 3D-printed constructs as potential therapies for spinal cord injury repair. A self-assembling peptide scaffold, RADA-16I, is used due to its established permissiveness to axon growth and ability to support vascularization. Immunohistochemistry assays verify that vascularized peptide scaffolds promote axon infiltration, attenuate inflammation and reduce astrogliosis. Furthermore, …

Evolution Of The Magnetic Properties On Van Der Waals Layered Magnets Via Pressure And Proton Irradiation, Rubyann Olmos

Open Access Theses & Dissertations

Probing the magnetism in quasi two-dimensional materials has the potential in driving their properties towards future use in spin electronic based devices. Studying such layered magnets will enable the scientific community to uncover tunable exotic phases such as superconductivity, quantum paramagnetism, etc. This work examines the influence of two types of external perturbations, namely, the pressure and proton irradiation, on the magnetic properties of several compounds in the van der Waals crystal family.

Pressure has been found to induce structural and magnetic phase transitions in many of these materials. Using hydrostatic pressure as a disorderless approach to manipulate the interlayer …

Structural, Charge Transport, Gas Sensing, Magnetic, Pseudocapacitive, And Electrocatalytic Properties Of Perovskite Oxides., Surendra Bahadur Karki

Electronic Theses and Dissertations

Perovskites are functional materials with the general formula ABO₃ (A = alkali, alkaline earth or lanthanoid cations and B = transition metal or main group cations). These materials are marked by a variety of crystal structures and interesting properties such as colossal magnetoresistance, ferroelectricity, multiferroicity, superconductivity, pseudocapacitance, gas sensing, charge transport, and electrocatalytic properties. The formula of perovskite can be written as AA’BB’O₆, when there is ordering between two cations over A and B-sites. Such compounds are called double perovskite oxides. Some amount of oxygen could be lost from crystal structure without decomposition of the phase. Such …

Magnetic And Structural Effects In Interfacial Magnetism: Molecular Magnets And Ferrimagnetic Alloys, Jenae E. Shoup

USF Tampa Graduate Theses and Dissertations

Magnetic thin films are important for technological applications such as giant magnetoresistance,spin valves and magnetic tunnel junctions. A key feature for these applications to be possible is the interface between two materials. We will be studying two types of thin film magnetism; interfaces between molecular carbon, C60, and non-magnetic/ferromagnetic material and two layers of ferrimagnetic rare earth/ transition metal alloys (RE/TM) that have similar composition to engineer a magnetic tunable interface.

One of the most unexpected spin-related properties of C60 is the emergence of room-temperature ferromagnetism in multilayer films of C60 and non-ferromagnetic transition metals such as Cu or Mn …

High Frequency Electron Spin Resonance Investigations On Quasi-Two-Dimensional Chromium Halide Magnets, Christian Saiz

Open Access Theses & Dissertations

Broadening the knowledge and understanding on the magnetic correlations in van der Waals layered magnets is critical in realizing their potential next-generation applications in devices such as spintronics. In this study, we employ high frequency (ν = 120 GHz, 240 GHz) electron spin resonance (ESR) spectroscopy on plate-like CrX3 (where X = Cl, Br, I) to gain insight into the magnetic interactions as a function of temperature (200 – 4.4 K) and the angle of rotation θ (degrees). We find that the temperature dependence of the ESR linewidth is well described by the Ginzburg-Landau critical model, indicative of antiferromagnetic correlations …

Synthesis And Physical Properties Of High Entropy Oxide Ceramics, Brianna L. Musicó

Doctoral Dissertations

Utilizing entropy as the driving force for stabilizing oxide materials offers a path for the discovery of innovative compounds with unique structure-property relations. The multi-cation approach inherent to high entropy oxides (HEOs) is expected to allow for the tailoring of physical properties that meet the requirements of potential applications. However, the intrinsic disorder and highly localized chemical environments of HEOs bring along new challenges. In order to shed light on the complexities associated multi-cation oxides, we have initiated a systematic study of polycrystalline HEO samples across multiple crystal systems. This work expands the multi-component concept to new compositions and crystal …

Securing Pint Glasses On Serving Trays With Magnetic Attachments, Jayden Commendatore

Senior Theses

It is extremely common for servers in the restaurant industry to have pint glasses slip off their serving tray, wasting both time and money for the restaurant. I have designed a sleeve attachment that will clip on to the bottom of a pint glass. The metal sleeve attachment will be attracted to a magnet placed into the serving tray. This increases the normal force of the pint glass, resulting in an increase in the friction force between the tray and sleeve attachment, and helping secure the glass to the tray. In order to optimize the design, the value of the …

Experimental Exploration Of Shared Magnetic Phases Between Diverse Systems Of Iron-Pnictide Superconductors, Ryan Scott Stadel

Graduate Research Theses & Dissertations

The exciting field of iron-pnictide superconductors offers unique opportunities for studying the relationship between magnetism and unconventional superconductivity. This is vital to developing an understanding of the microscopic origin of high-temperature superconductivity, which is itself an important step in harnessing such a potentially revolutionary technology.

Polycrystalline and crystalline samples are synthesized over a diverse collection of related iron-pnictide systems including (Ca,Sr,Ba)1-xNaxFe2As2, Ba(Fe1-xCox)2As2 (122s), and LaFeAs1-xPxO, and TbFeAs1-xPxO (1111s). These compounds are characterized through various types of neutron and x-ray diffraction on multiple instruments, as well as muon spin resonance, and magnetic susceptibility measurements.

A thorough investigation into the conditions under …

Development Of Software Tools And Experimental In Situ Electron Spin Resonance For Characterizing The Magnetic And Electrocatalytic Properties Of Transition Metal Chalcogenide Crystals, Jose Armando Delgado

Open Access Theses & Dissertations

Studying the magnetic properties and crystal defects of transition metal chalcogenide crystals is of paramount importance for utilizing them for next generation spintronics devices and hydrogen evolution reaction catalysts. Hydrothermally grown transition metal chalcogenide nanocrystals (MoS2, Ru2S3, Rh2S3, Co2S8) were chosen as catalysts for the hydrogen evolution reaction due to their low dimensionality and previous utilization as catalysts for hydrodesulfurization. The relationship between crystal defect sites and catalytic activity must be discerned to maximize the efficiency of hydrogen production during the hydrogen evolution reaction. ESR spectroscopy was utilized as a spin sensitive technique to study the defects and local changes …

Investigations On Hydrothermally Synthesized Co3o4/Mnxco3-Xo4 Core-Shell Nanoparticles, Ning Bian

MSU Graduate Theses

Two different morphologies (pseudo-spherical shaped or PS type and hexagonal nanoplate shaped or NP type) and two different concentrations (0.07 M and 0.1 M) of manganese incorporated Co₃O₄@Mn_xCo_3-xO₄ core-shell nanoparticles (CSNs) were investigated, respectively. The motivation of this work is to investigate the magnetic properties of, and specifically the exchange bias, between different shaped CSNs and between different Mn-doped CSNs. A two-step synthesis method was utilized to obtain the CSNs: a soft chemical approach was used to obtain Co₃O₄ nanoparticles and a hydrothermal nano-phase epitaxy was used to …

Magnetic And Catalytic Properties Of Transition Metal Doped Mos2 Nanocrystals, Luis Martinez

Open Access Theses & Dissertations

Magnetism and catalytic activity of nanoscale layered two-dimensional (2D) transition metal dichalcogenides (TMDs) have gained an increasing research interest in the recent past. To broaden the current knowledge and understanding on this subject, in this work, together with my collaborators, I study the magnetic and electrocatalytic properties of hydrothermally grown pristine and transition metal doped (10% of Co, Ni, Fe and Mn) 2H-MoS2 nanosheets/nanocrystals (NCs), with the particle size of 25-30 nm. A broad range of experimental measurements such as x-ray diffraction, transmission electron microscopy, x-ray photo absorption spectroscopy, Raman spectroscopy, magnetic, catalytic and electron spin resonance have been employed …

Characterizing Local Order And Physical Properties Of Rare Earth Complex Oxides, Thomas Jacob Shamblin

Doctoral Dissertations

With more than 500 compositions, materials possessing the pyrochlore structure have a myriad of technological applications and physical phenomena. Three of the most noteworthy properties are the structure’s ability to resist amorphization making it a possible host matrix for spent nuclear fuel, its exotic magnetic properties arising from geometric frustration, and fast ionic conductivity for solid-oxide fuel cell applications. This work focuses on these three aspects of the pyrochlore’s many potential uses. Structural characterization revealed that pyrochlore-type oxides have a tendency to disorder from a high symmetry cubic structure to a lower symmetry orthorhombic arrangement in response to a variety …

Nanophotonics For Dark Materials, Filters, And Optical Magnetism, Mengren Man

Open Access Dissertations

Research on nanophotonic structures for three application areas is described, a near perfect optical absorber based on a graphene/dielectric stack, an ultraviolet bandpass filter formed with an aluminum/dielectric stack, and structures exhibiting homogenizable magnetic properties at infrared frequencies. The graphene stack can be treated as a effective, homogenized medium that can be designed to reflect little light and absorb an astoundingly high amount per unit thickness, making it an ideal dark material and providing a new avenue for photonic devices based on two-dimensional materials. Another material stack arrangement with thin layers of metal and insulator forms a multi-cavity filter that …

Sensing Gyroscopic Properties Of Rotating Magnetic Nanoparticles In Solution, Brian Gerald Krug

Dissertations

A new sensor using magnetic nanoparticles and rotating magnetic fields has been developed. By spinning the nanoparticles in a rotating magnetic field, it is feasible to infer angular position and inertia if an external force is applied to the system. The nanoparticles are treated as a multitude of miniature gyroscopes whose overall effect can be combined as one single gyroscope. Two sensors were built to test the feasibility, both containing Fe3O4 nanoparticles.

The typical input current was 250 milliamps. When the sensor deviated from its magnetic axis by a small angle, the input current changed between 1 and 2 milliamps …

Exchange Mechanisms In Macroscopic Ordered Organic Magnetic Semiconductors, Naveen Rawat

Graduate College Dissertations and Theses

Small molecule organic semiconductors such as phthalocyanines and their derivatives represent a very interesting alternative to inorganic semiconductor materials for the development of flexible electronic devices such as organic thin field effect transistors, organic Light Emitting Diodes and photo-voltaic cells. Phthalocyanine molecules can easily accommodate a variety of metal atoms as well in the central core of the molecule, resulting in wide range of magnetic properties. Exploration of optical properties of organic crystalline semiconductors thin films is challenging due to sub-micron grain sizes and the presence of numerous structural defects, disorder and grain boundaries. However, this can be overcome by …

Analysis Of Critical Behavior In Magnetic Materials, Dustin David Belyea

USF Tampa Graduate Theses and Dissertations

This work contains a broad study of a variety of magnetic materials undergoing second order phase transitions. In general this leads to an overall increase in information and analytical methods to further the field of magnetocalorics. Specifically, critical aspects of magnetocaloric materials were compared within systems in relation to structure, stoichiometry, magnetic minority phases and magnetic contaminants. Detailed analyses were developed to quantify techniques which were in the past used mainly in a qualitative way, leading to a more complete understanding of how critical phenomena impacts the magnetocaloric response.

Metal Oxide Growth, Spin Precession Measurements And Raman Spectroscopy Of Cvd Graphene, Akitomo Matsubayashi

Legacy Theses & Dissertations (2009 - 2024)

The focus of this dissertation is to explore the possibility of wafer scale graphene-based spintronics. Graphene is a single atomic layer of sp2 bonded carbon atoms that has attracted much attention as a new type of electronic material due to its high carrier mobilities, superior mechanical properties and extremely high thermal conductivity. In addition, it has become an attractive material for use in spintronic devices owing to its long electron spin relaxation time at room temperature. This arises in part from its low spin-orbit coupling and negligible nuclear hyperfine interaction. In order to realize wafer scale graphene spintronics, utilization of …

Magnetization Dynamics And Related Phenomena In Nanostructures, Sayan Chandra

USF Tampa Graduate Theses and Dissertations

Collective magnetic behavior in nanostructures is a phenomenon commonly observed in various magnetic systems. It arises due to competing inter/intra–particle interactions and size distribution and can manifest in phenomena like magnetic freezing, magnetic aging, and exchange bias (EB) effect. In order to probe these rather complex phenomena, conventional DC and AC magnetic measurements have been performed along with radio–frequency transverse susceptibility (TS) measurements. We also demonstrate the magnetic entropy change as a parameter sensitive to subtle changes in the magnetization dynamics of nanostructures. The focus of this dissertation is to study the collective magnetic behavior in core-shell nanostructures of Fe/γ–Fe …

Structure And Dynamics Of High Temperature Superconductors, Jennifer Lynn Niedziela

Doctoral Dissertations

High temperature superconductivity in iron based compounds has presented a series of complex problems to condensed matter physics since being discovered in 2008. The stalwart basis of condensed matter physics is the “strength in numbers" aspect of crystalline periodicity. Perfect crystalline periodicity has made possible the reduction of the questions of structural and electronic properties to single dimensions, increasing the tractability of these problems. Nevertheless, modern complex materials stretch these assumptions to their limits, and it is at this point where our work starts. Using neutron and x-ray scattering, we have conducted a series of studies on the structural disorder …

Morphology-Properties Studies In Laser Synthesized Nanostructured Materials, Nozomi Shirato

Doctoral Dissertations

Synthesis of well-defined nanostructures by pulsed laser melting is an interesting subject from both a funda- mental and technological point of view. In this thesis, the synthesis and functional properties of potentially useful materials were studied, such as tin dioxide nanostructured arrays, which have potential applications in hydrogen gas sensing, and ferromagnetic Co nanowire and nanomagnets, which are fundamentally im- portant towards understanding magnetism in the nanoscale. First, the formation of 1D periodic tin dioxide nanoarrays was investigated with the goal of forming nanowires for hydrogen sensing. Experimental obser- vations combined with theoretical modeling successfully explained the mechanisms of structure …