Dissertations / Theses on the topic 'In-Plane magnetized thin films'

La demande de stockage de données a connu une croissance exponentielle, alimentée par la dépendance croissante du monde à l'égard de l'information numérique. Cette croissance a catalysé le développement de technologies plus rapides et plus éco-énergétiques. Ce développement coïncide avec les objectifs de la spintronique, un domaine visant à réduire la consommation d'énergie dans le stockage de données magnétiques en explorant des alternatives basées sur le spin. En conséquence, des recherches approfondies ont été consacrées à la manipulation de la magnétisation (c'est-à-dire les spins), qui est au cœur de la spintronique, formant un programme de recherche substantiel et durable. La vitesse et l'efficacité de cette manipulation dépendent des méthodes d'écriture utilisées et des propriétés des matériaux magnétiques impliqués, nécessitant ainsi une compréhension approfondie des mécanismes de manipulation sous-jacents. Parmi les différentes techniques d'écriture, l'utilisation d'impulsions laser ultracourtes (femtosecondes) a attiré une attention considérable en raison de sa capacité à exciter rapidement la magnétisation à l'échelle femtoseconde. Une seule impulsion laser femtoseconde a été démontrée pour induire une inversion complète de la magnétisation dans les matériaux magnétiques, un phénomène connu sous le nom de commutation optique complète indépendante de l'hélicité (AO-HIS). Cependant, le mécanisme sous-jacent et les critères de l'AO-HIS restent incomplètement compris. De plus, depuis le premier rapport de l'AO-HIS, cet effet a principalement été observé dans un groupe spécifique de matériaux magnétiques présentant une anisotropie magnétique perpendiculaire. De plus amples efforts et études sont nécessaires pour élargir l'applicabilité de l'AO-HIS. Pour atteindre cet objectif, cette thèse se concentre sur l'étude de l'AO-HIS dans une gamme de matériaux ferrimagnétiques et ferromagnétiques caractérisés par une anisotropie magnétique dans le plan. Nous utilisons des impulsions laser femtosecondes pour induire l'inversion de la magnétisation dans ces matériaux. De plus, nous entreprenons une exploration systématique visant à comprendre l'AO-HIS en modifiant les propriétés magnétiques des hétérostructures magnétiques. Cette manipulation comprend la variation des concentrations d'alliage, des températures de Curie, des épaisseurs et du type de couches magnétiques. Nous considérons nos résultats comme cruciaux d'un point de vue fondamental. Les résultats expérimentaux de cette thèse sont présentés dans trois chapitres (Chapitres 4 à 6). Dans le Chapitre 4, nous avons largement discuté de la commutation optique complète déterministe observée dans une large gamme de concentrations d'alliage et d'épaisseurs dans les films minces de GdCo magnétisés dans le plan, en utilisant un système de microscopie à effet Kerr magnéto-optique basé sur un laser. Les Chapitres 5 et 6 explorent le processus de transition des multiples aux inversions uniques de la magnétisation dans les matériaux ferromagnétiques magnétisés dans le plan, induit par des impulsions de courant de spin optiquement générées
The demand for data storage has experienced exponential growth, driven by the world's increasing reliance on digital information. This growth has catalyzed the development of faster and more energy-efficient technologies. This development coincides with the objectives of spintronics, a field aimed at reducing energy consumption in magnetic data storage by exploring spin-based alternatives. As a result, extensive research has been dedicated to the manipulation of magnetization (i.e., spins), which lies at the heart of spintronics, forming a substantial and enduring research agenda. The speed and efficiency of this manipulation depend on the methods of writing employed and the properties of the magnetic materials involved, thus requiring a comprehensive understanding of the underlying manipulation mechanisms. Among the various writing techniques, the utilization of ultrashort (femtosecond) laser pulses has gained considerable attention for its capability to rapidly excite magnetization on the femtosecond timescale. A single femtosecond laser pulse has been demonstrated to induce full magnetization reversal in magnetic materials, a phenomenon known as all-optical helicity-independent switching (AO-HIS). However, the underlying mechanism and criteria for the AO-HIS remain incompletely understood. Moreover, since the initial report of AO-HIS, this effect has mainly been observed in a specific group of magnetic materials exhibiting perpendicular magnetic anisotropy. Further endeavors and studies are necessary to broaden the applicability of AO-HIS. In pursuit of this goal, this thesis focuses on investigating AO-HIS in a range of ferrimagnetic and ferromagnetic materials characterized by in-plane magnetic anisotropy. We employ femtosecond laser pulses to drive magnetization reversal in these materials. Furthermore, we undertake a systematic exploration aimed at comprehending AO-HIS by altering the magnetic properties of magnetic heterostructures. This manipulation includes varying alloy concentrations, Curie temperatures, thicknesses, and the type of magnetic layers. We consider our findings crucial from a fundamental perspective. The experimental findings of this thesis are presented in three chapters (Chapters 4 to 6). In Chapter 4, we extensively discussed the deterministic AO-HIS observed in a broad range of alloy concentrations and thicknesses in in-plane magnetized GdCo thin films, utilizing a laser-based magneto-optic Kerr effect microscopy system. Chapters 5 and 6 delve into the recipe of transitioning from multiple to single magnetization reversals in in-plane magnetized ferromagnetic materials, induced by optically generated spin current pulses

The term Gossamer is used to describe ultra-lightweight spacecraft structures that solve the aerospace challenge of obtaining maximum performance while reducing the launch costs of the spacecraft. Gossamer structures are extremely compliant, which complicates control design and ground testing in full scale. One approach is to design and construct smaller test articles and verify their computational models experimentally, so that similar computational models can be used to predict the dynamic performance of full-scale structures. Though measurement of both in-plane and out-of-plane displacements is required to characterize the dynamic response of the surface of these structures, this thesis lays the groundwork for dynamic measurement of the in-plane component. The measurement of thin films must be performed using non-contacting sensors because any contacting sensor would change the dynamics of the structure. Moreover, the thin films dealt with in this work are coated with either gold or aluminum for special applications making the film optically smooth and therefore requiring a surface pattern. A Krypton Fluoride excimer laser system was selected to fabricate patterns on thin-film mirror test articles. Parameters required for pattern fabrication were investigated. Effects of the pattern on the thin-film dynamics were studied using finite element analysis. Photogrammetry was used to study the static in-plane displacement of the thin-film mirror. This was performed to determine the feasibility of the photogrammetric approach for future dynamic tests. It was concluded that photogrammetry could be used efficiently to quantify dynamic in-plane displacement with high-resolution cameras and sub-pixel target marking.

The temperature and field dependence of the magnetization of epitaxial, undoped anatase TiO2 thin films on SrTiO3 substrates was investigated. Low-energy ion irradiation was used to modify the surface of the films within a few nanometers, yet with high enough energy to produce oxygen and titanium vacancies. The as-prepared thin film shows ferromagnetism which increases after irradiation with low-energy ions. An optimal and clear magnetic anisotropy was observed after the first irradiation, opposite to the expected form anisotropy. Taking into account the experimental parameters, titanium vacancies as di-Frenkel pairs appear to be responsible for the enhanced ferromagnetism and the strong anisotropy observed in our films. The magnetic impurities concentrations was measured by particle-induced X-ray emission with ppm resolution. They are ruled out as a source of the observed ferromagnetism before and after irradiation.

Thesis (Ph. D.) -- University of Maryland, College Park, 2006.
Thesis research directed by: Electrical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

In the present thesis, magnetization reversal in both out-of-plane and in-plane magnetized thin lms and in devices fabricated out of those lms are explored. Pt/Co/Pt stacks with ultrathin Co layer were in-estimated initially for understanding their magnetic properties in this thesis. These perpendicular magnetized systems are good candidates for magnetic hard disc drives due to their large anisotropy, which may allow miniaturization of magnetic data storage devices. The spin Hall e ect mediated current-induced magnetization reversal in patterned Pt/Co/Pt devices were extensively investigated. Investigation of the magnetization reversal by means of a current instead of a magnetic eld is necessary to explore the possibilities of solid state magnetic memory devices. This is the primary motivation behind the investigation of current-induced magnetization reversal in Pt/Co/Pt system, in this thesis. Another important proposal for magnetic data storage is the race track memory, where the domain walls separating magnetic domains (in in-plane or out-of-plane magnetized materials) are moved by using a current. This involves a great deal of understanding of the domain wall motion in Nano-conduits under applied magnetics ends, and currents and also its interaction with engineered geometrical features. In this thesis work, magnetic led-driven domain wall pinning and deepening experiments on in-plane magnetized nanowires of perm alloy were performed to un-distend this interaction and the e act of domain wall chirality. In chapter 1, a general introduction to di errant data storage technologies and the current progress in the leg of spintronic is presented. This will highlight a perspective of this thesis work with respect to the present day research in spintronic and magnetization reversal studies. In chapter 2, a basic background of magnetism using the micromag-netic framework is illustrated. A brief introduction to magnetic domain walls is also presented. The Landau-Lifshitz-Gilbert dynamical equation is discussed and some case studies applied to a single domain particle with uniaxial anisotropy under the effect of spin-orbit torque are illu trated. The basics of spin-orbit coupling leading to spin Hall e ect is also explain In chapter 3, most of the essential experimental tools along with their basic working principles are described. Extensive e orts have been in-vested in designing and building the experimental tools. These include custom designs of a sputter deposition system, an ultra-high vacuum chamber for pulsed laser ablation, a magneto-optic Kerr e ect magne-tometer, a Kerr imaging system and a magneto-transport setup. All of these experimental setups have been automated, details of which are brie y discussed in this chapter. The Kerr imaging system was designed to measure hysteresis loops, observe domain wall motion and to measure domain wall velocity under applied magnetic elds and electric current. The magneto-transport setup was used for studying the domain wall pinning and depinning experiments in permalloy nanowires. In chapter 4, the optimization process for obtaining perpendicular mag-netic anisotropy in Pt/Co/Pt lms is described. The spin reorientation transition with varying thickness of Co (from 1.5 nm down to 0.35 nm) was studied. The magnetization easy axis direction changes from in-plane to out-of-plane as the thickness of Co is reduced. The dependence of Curie temperatures of ultrathin Co lms, with thickness as low as 0.35 nm, on the underlayer Pt thickness and its crystallinity was studied in detail. The e act of Ta but err layer on the texture of the Pt lm, and on the Curie temperature of the Pt/Co/Pt system was evaluated. To gain further insight of the role of the bottom Pt/Co and the top Co/Pt interfaces, ultrathin Cu lbs were inserted at the respective interfaces, and the anisotropy and magnetization reversal behaviour of these lbs were investigated. In chapter 5, studies on current-induced magnetization reversal in mi-corn sized wires of Pt/Co/Pt trilete is presented. The spin Hall e act assisted spin-orbit torque was used to reversibly switch the magnetization of these devices with and without the help of an external magnetic led. Since both the top and bottom layers are Pt, any contribution from Rashia e act towards spin-orbit torque could be ignored. By preparing devices with unequal top and bottom Pt thicknesses, a net spin-orbit torque could be applied to the magnetization of the Co layer. The thickness gradient/induced anisotropy in the Co layer was utilized to experimentally investigate current-induced deterministic switching. Sin-gel domain simulations with spin-orbit torque were also carried out to understand the mechanism of deterministic switching of magnetization in Pt/Co/Pt devices. This study is expected to have made sign cant contributions and to open up the possibilities of further investigation in the studies of spin-orbit torque in Pt/Co/Pt systems for solid state magnetic memory devices. In chapter 6, magnetic led-induced reversal in systems with in-plane magnetic anisotropy is presented. Here the e act of the width of a Nanos-trip on the anisotropy of a soft magnetic material like perm alloy was in-estimated. By introducing a nucleation pad to one end of the perm alloy nanowire, a single domain wall was generated at the junction with apple-cation of a proper magnetic led sequence. This domain wall could be in-jested into the nanowire by a magnetic led and pinned at a geometrical constriction inside the nanowire. The statistics of domain wall pinning and deepening processes indicated two di errant types of domain walls involved in the reversal process. With the assistance of micro magnetic simulations the domain walls were ident end as vortex walls of di errant chirality’s. Thus the interaction of domain walls with a Nano constriction and its dependence on the chirality of domain walls are understood. In chapter 7, a brief summary of the results obtained during the course of investigations is presented. An outlook presented at the end will help the readers of this thesis to understand the important research problems in this area and their potential future aspects.

In the present thesis, magnetization reversal in both out-of-plane and in-plane magnetized thin lms and in devices fabricated out of those lms are explored. Pt/Co/Pt stacks with ultrathin Co layer were in-estimated initially for understanding their magnetic properties in this thesis. These perpendicular magnetized systems are good candidates for magnetic hard disc drives due to their large anisotropy, which may allow miniaturization of magnetic data storage devices. The spin Hall e ect mediated current-induced magnetization reversal in patterned Pt/Co/Pt devices were extensively investigated. Investigation of the magnetization reversal by means of a current instead of a magnetic eld is necessary to explore the possibilities of solid state magnetic memory devices. This is the primary motivation behind the investigation of current-induced magnetization reversal in Pt/Co/Pt system, in this thesis. Another important proposal for magnetic data storage is the race track memory, where the domain walls separating magnetic domains (in in-plane or out-of-plane magnetized materials) are moved by using a current. This involves a great deal of understanding of the domain wall motion in Nano-conduits under applied magnetics ends, and currents and also its interaction with engineered geometrical features. In this thesis work, magnetic led-driven domain wall pinning and deepening experiments on in-plane magnetized nanowires of perm alloy were performed to un-distend this interaction and the e act of domain wall chirality. In chapter 1, a general introduction to di errant data storage technologies and the current progress in the leg of spintronic is presented. This will highlight a perspective of this thesis work with respect to the present day research in spintronic and magnetization reversal studies. In chapter 2, a basic background of magnetism using the micromag-netic framework is illustrated. A brief introduction to magnetic domain walls is also presented. The Landau-Lifshitz-Gilbert dynamical equation is discussed and some case studies applied to a single domain particle with uniaxial anisotropy under the effect of spin-orbit torque are illu trated. The basics of spin-orbit coupling leading to spin Hall e ect is also explain In chapter 3, most of the essential experimental tools along with their basic working principles are described. Extensive e orts have been in-vested in designing and building the experimental tools. These include custom designs of a sputter deposition system, an ultra-high vacuum chamber for pulsed laser ablation, a magneto-optic Kerr e ect magne-tometer, a Kerr imaging system and a magneto-transport setup. All of these experimental setups have been automated, details of which are brie y discussed in this chapter. The Kerr imaging system was designed to measure hysteresis loops, observe domain wall motion and to measure domain wall velocity under applied magnetic elds and electric current. The magneto-transport setup was used for studying the domain wall pinning and depinning experiments in permalloy nanowires. In chapter 4, the optimization process for obtaining perpendicular mag-netic anisotropy in Pt/Co/Pt lms is described. The spin reorientation transition with varying thickness of Co (from 1.5 nm down to 0.35 nm) was studied. The magnetization easy axis direction changes from in-plane to out-of-plane as the thickness of Co is reduced. The dependence of Curie temperatures of ultrathin Co lms, with thickness as low as 0.35 nm, on the underlayer Pt thickness and its crystallinity was studied in detail. The e act of Ta but err layer on the texture of the Pt lm, and on the Curie temperature of the Pt/Co/Pt system was evaluated. To gain further insight of the role of the bottom Pt/Co and the top Co/Pt interfaces, ultrathin Cu lbs were inserted at the respective interfaces, and the anisotropy and magnetization reversal behaviour of these lbs were investigated. In chapter 5, studies on current-induced magnetization reversal in mi-corn sized wires of Pt/Co/Pt trilete is presented. The spin Hall e act assisted spin-orbit torque was used to reversibly switch the magnetization of these devices with and without the help of an external magnetic led. Since both the top and bottom layers are Pt, any contribution from Rashia e act towards spin-orbit torque could be ignored. By preparing devices with unequal top and bottom Pt thicknesses, a net spin-orbit torque could be applied to the magnetization of the Co layer. The thickness gradient/induced anisotropy in the Co layer was utilized to experimentally investigate current-induced deterministic switching. Sin-gel domain simulations with spin-orbit torque were also carried out to understand the mechanism of deterministic switching of magnetization in Pt/Co/Pt devices. This study is expected to have made sign cant contributions and to open up the possibilities of further investigation in the studies of spin-orbit torque in Pt/Co/Pt systems for solid state magnetic memory devices. In chapter 6, magnetic led-induced reversal in systems with in-plane magnetic anisotropy is presented. Here the e act of the width of a Nanos-trip on the anisotropy of a soft magnetic material like perm alloy was in-estimated. By introducing a nucleation pad to one end of the perm alloy nanowire, a single domain wall was generated at the junction with apple-cation of a proper magnetic led sequence. This domain wall could be in-jested into the nanowire by a magnetic led and pinned at a geometrical constriction inside the nanowire. The statistics of domain wall pinning and deepening processes indicated two di errant types of domain walls involved in the reversal process. With the assistance of micro magnetic simulations the domain walls were ident end as vortex walls of di errant chirality’s. Thus the interaction of domain walls with a Nano constriction and its dependence on the chirality of domain walls are understood. In chapter 7, a brief summary of the results obtained during the course of investigations is presented. An outlook presented at the end will help the readers of this thesis to understand the important research problems in this area and their potential future aspects.

abstract: Polycrystalline magnetite thin films were deposited on large area polymer substrates using aqueous solution based spin-spray deposition (SSD). This technique involved the hydrolysis of precursor salt solutions at low temperatures (70-100°C). The fundamental mechanisms and pathways in crystallization and evolution of the film microstructures were studied as a function of reactant chemistry and reactor conditions (rotation rate, flow rates etc.). A key feature of this method was the ability to constantly supply fresh solutions throughout deposition. Solution flow due to substrate rotation ensured that reactant depleted solutions were spun off. This imparted a limited volume, near two-dimensional restriction on the growth process. Film microstructure was studied as a function of process parameters such as liquid flow rate, nebulizer configuration, platen rotation rate and solution chemistry. It was found that operating in the micro-droplet regime of deposition was a crucial factor in controlling the microstructure. Film porosity and substrate adhesion were linked to the deposition rate, which in-turn depended on solution chemistry. Films exhibited a wide variety of hierarchically organized microstructures often spanning length scales from tens-of-nanometers to a few microns. These included anisotropic morphologies such as nanoplates and nanoblades, that were generally unexpected from magnetite (a high symmetry cubic solid). Time resolved studies showed that the reason for complex hierarchy in microstructure was the crystallization via non-classical pathways. SSD of magnetite films involved formation of precursor phases that subsequently underwent solid-state transformations and nanoparticle self-assembly. These precursor phases were identified and possible reaction mechanisms for the formation of magnetite were proposed. A qualitative description of the driving forces for self-assembly was presented.
Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2018

Thesis (M.S.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Dept. of Electrical and Computer Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

碩士
國立雲林科技大學
材料科技研究所
107
In this study, Co40Fe40V10B10 thin-films were sputtered onto a glass substrate and Silicon substrate with various thicknesses from 10 to 40 nm at room temperature (RT). The microstructure and low-frequency alternative-current magnetic susceptibility (χac) was examined using an χac analyzer (XacQuan, MagQu) and optical characteristics were investigated. The study of the cobalt, vanadium, iron alloy known commercially. This alloy contains 40% , 40% iron and the balance essentially 20% vanadium. The vanadium, cobalt and iron-containing alloy is finding increasing use as a rotor and stator material in electrical generators for aircraft because of its high magnetic flux carrying capacity which makes it possible to achieve a considerable reduction in weight of the units in which components of the alloy are employed. As for vanadium alloys, alloys composed of other alloying elements based on vanadium are added. Vanadium alloys have a fast neutron absorption cross section, good resistance to liquid metal lithium, sodium, potassium, etc., as well as good strength and plasticity, good processing properties, resistance to radiation embrittlement, anti-irradiation expansion It has good dimensional stability under irradiation and is an important reactor structural material. Typical vanadium alloys are V- 15Ti-7.5Ct, V-15Cr-5Ti, V-10Ti, V-20Ti, V-9Cr-3Fe-1.5Zr-0.05C. These vanadium alloys are used as fuel cladding and structural elements for liquid metal cooled fast breeder reactors. The purpose of this study is to understand that Co40Fe40V10B10 has various thicknesses to determine its microstructure and electro-optical properties. X-ray diffraction (XRD) indicated that each Co40Fe40V10B10 thin-films. It shows that the peak is the largest when the film thickness is 30 nm, and the texture structure strength is better. From this, it can be found that at 30 nm, the intensity of the reflected iv light is the strongest, and the crystallinity of the grown film is better. We can find that the glass film with a thickness of 30 nm has the largest coercive force and the best squareness. The saturation magnetization amount 564 (emu/cm3) is compared with other films of different thicknesses. Significantly larger trend. The low-frequency AC susceptibility (χac) was observed and studied. As the frequency increased, χac decreased sharply. The results showed that the optimal resonance frequency of Co40Fe40V10B10 film was lower than 1000 Hz, which indicates that Co40Fe40V10B10 is suitable for low-frequency magnetic component applications. The Co40Fe40V10B10 film was subjected to a measurement of transmittance and reflectance using a micro spectrometer (Spectrometer). It was found that the thinner the film thickness measured by the transmittance, the higher the transmittance, which is about 40% or more. It is reasonable to conclude that the thinner the film thickness is, the easier it is to reflect the incident light, and the high transmittance and low absorption rate are suitable for optical applications.

碩士
國立交通大學
光電工程系所
92
We study the effect of biaxial stress on the ZnO thin films by growing those onto Al2O3 (001), Si (111) and SiC (001). We use a third harmonic of Nd:YVO4 laser (��=355nm) to measure the in-plane optical gain of high-quality ZnO epilayers on Al2O3. From reflection high energy electron diffraction (RHEED) observation and ���{rocking curve, we found qualities of ZnO/Al2O3 and ZnO/SiC are better. Phi scans for (202) peaks of three samples indicate six-fold symmetry and epitaxial growth of ZnO thin films onto Al2O3 and SiC except Si (111). We have investigated X-ray ��-2�� scan for (002) and (110) reflections to determine c- and a-axis lattice constants of ZnO thin films on different substrates. With room-temperature (RT) PL spectra of three samples, we can derive the stress states in films. The thermal stress can also play a key role in deciding the residual strain in film. Beside we found that the inelastic exciton-exciton (ex-ex) scattering dominantly contributes to the optical gain at excitation densities, 4.585 MW/cm2 and the electron-hole plasma (EHP) state at excitation densities, 8.45MW/cm2. Maximum gain of 187 cm-1 at the excitation density of 25.3 MW/cm2 is obtained. With increasing excitation, density contribution from the EHP state gradually takes over at the lower energy side in the optical gain spectrum.

碩士
國立清華大學
物理系
104
As traditional bulk thermoelectric (TE) materials are usually applied to large-scale heat management, thin film thermoelectric materials are often used to manage small-scale heat in the field of microelectronics. Bismuth telluride based compound materials are well-known for its high ZT value at room temperature regime. Previous studies have shown that a current-assisted thermal annealing was able to improve thermoelectric properties of Bi-Te based thin films. Yet, the thermal conductivity of such thin film materials is not fully investigated. In this research, we extended the conventional 3omega technique and developed a method, which considers the interfacial thermal resistance, to measure the in-plane thermal conductivity of thermoelectric thin films. Silicon dioxide thin films were used to verify the feasibility of our method, and subsequently, we measured the in-plane thermal conductivity of TE thin films. P-type Bio.5Sb1.5Te3 thin films were deposited by sputtering on a thermally oxidized silicon substrate. A current-assisted thermal annealing is applied to the thin films at a current density of 2500A/cm2 when annealed at 300 ◦C. The electrically stressed Bio.5Sb1.5Te3 thin films have higher Seebeck coefficient, higher mobility and lower carrier concentration than the thermally annealed films. In addition, both cross-plane (ky) and in-plane (kx) thermal conductivities of the electrically stressed TE films were found to be larger than those of the thermally annealed films. The electrically stressed films shows a high anisotropy in thermal conductivity with a ratio kx/ky equal to 1.8. According to the microstructural and thermoelectric analysis, the measured anisotropy is mostly attributed to the development of (00l) film texture, as other factors show little impact on such results.