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Marcellini, Moreno. "Magnetic Ordering in Layered Magnets." Doctoral thesis, Uppsala universitet, Materialfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8604.
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The preparation of layered magnets needs the knowledge of growth techniques which are focused on the growth of Fe/V(001) superlattices. Such films have been structurally investigated by X-rays reflectivity and diffraction. The magnetic investigations have been carried out by magneto-optic Kerr effect (MOKE), Superconducting Quantum Interference Device (SQUID) magnetometry and polarized neutron reflectivity (PNR). This latter technique has been used in cooperation with the Institute Laue Langvin (Grenoble, France) and Ruhr Universität (Bochum, Germany). The cross-over in universality class is shown in a series of layered magnets where a δ-doping layer of Fe has been embedded between two layers of Pd showing that the magnetization depends on the effective magnetic thickness of the polarized Pd. A model for the cross-over has been developed in terms of magnetic excitations. The interlayer exchange coupling (IEC) mediated by a non-magnetic spacer has been reviewed focusing the attention on the recent theoretical and experimental works based on Fe/V(001) superlattices. The IEC can be tailored at will by reversibly alloying of the spacer with H: this has been proved in Fe/V(001) double layers showing that in the two dimensional limit, the universality class is not affected by the coupling. The magnetic order-disorder transitions in Fe/V(001) superlattices do not seem to belong to any universality class. A phenomenological model which accounts for the effective coupling at the boundaries has been developed. The influence of the inherent ordering temperatures of single magnetic layers has been investigated in Fe/V(001) superlattices proving that the weakest ferromagnetic layer affects the overall magnetic ordering. A new kind of layered magnet has been developed to increase the effect of the boundaries. PNR measurements show that the universality class depends on which length-scale is investigated.
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Riley, Melissa Alessandra. "The use of magnets in biomedical applications." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364498.
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Etzkorn, Stephen J. "Magnetic relaxation in organic-based magnets." Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1044548603.
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Thesis (Ph. D)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xvi, 134 p. : ill. (some col.). Includes abstract and vita. Advisor: Arthur J. Epstein, Dept. of Physics. Includes bibliographical references (p. 128-134).
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Klešč, Tania. "Neodimio magnetų eksperimentinis tyrimas." Bachelor's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130821_115730-10514.
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Bakalauro darbą „ Neodimio magnetų eksperimentinis tyrimas“ sudaro įvadas, keturi skyriai, išvados, priedai ir literatūros sąrašas. Šio darbo apimtis 30 puslapių. Darbe yra 26 paveikslėliai ir 1 lentelė.Įvade iškeliama darbo problema, tikslai ir uždaviniai. Pirmajame skyriuje pateikta literatūros analizė. Antrajame skyriuje aprašoma eksperimento metodika. Trečiajame skyriuje pateikti sistemų su neodimio magnetais tyrimo rezultatai. Ketvirtajame skyriuje pateikta eksperimento rezultatų analizė. Darbo pabaigoje pateiktos išvados apibendrinančios atliktą darbą ir pateikti pasiūlymai, kur būtų galima panaudoti neodimio magnetus.The final bachelor‘s work “Experimental analysis of neodymium magnets” consist of introduction, four chapters, conclusions and references. The work consists of 30 pages. There are 26 images and 1 table.Problem of the research along with objectives and goals are provided in the introduction of this work. The first chapter provides analysis of literature. The second chapter is about methodology of experiment. The third chapter provides the results of systems of neodymium magnets. The fourth chapter provides analysis of the experiment results. At the end of the work there are conclusions and suggestions about neodymium magnets usage.
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Krupskaya, Yulia. "Magnetic Properties of Molecular and Nanoscale Magnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-73289.
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The idea of miniaturizing devices down to the nanoscale where quantum ffeffects become relevant demands a detailed understanding of the interplay between classical and quantum properties. Therefore, characterization of newly produced nanoscale materials is a very important part of the research in this fifield. Studying structural and magnetic properties of nano- and molecular magnets and the interplay between these properties reveals new interesting effects and suggests ways to control and optimize the respective material. The main task of this thesis is investigating the magnetic properties of molecular magnetic clusters and magnetic nanoparticles recently synthesized by several collaborating groups. This thesis contains two main parts focusing on each of these two topics.
In the first part the fundamental studies on novel metal-organic molecular complexes is presented. Several newly synthesized magnetic complexes were investigated by means of different experimental techniques, in particular, by electron spin resonance spectroscopy. Chapter 1 in this part provides the theoretical background which is necessary for the interpretation of the effects observed in single molecular magnetic clusters. Chapter 2 introduces the experimental techniques applied in the studies. Chapter 3 contains the experimental results and their discussion. Firstly, the magnetic properties of two Ni-based complexes are presented. The complexes possess different ligand structures and arrangements of the Ni-ions in the metal cores. This difffference dramatically affffects the magnetic properties of the molecules such as the ground state and the magnetic anisotropy. Secondly, a detailed study of the Mn2Ni3 single molecular magnet is described. The complex has a bistable magnetic ground state with a high spin value of S = 7 and shows slow relaxation and quantum tunnelling of the magnetization. The third section concentrates on a Mn(III)-based single chain magnet showing ferromagnetic ordering of the Mn-spins and a strong magnetic anisotropy which leads to a hysteretic behavior of the magnetization. The last section describes a detailed study of the static and dynamic magnetic properties of three Mn-dimer molecular complexes by means of static magnetization, continuous wave and pulse electron spin resonance measurements. The results indicate a systematic dependence of the magnetic properties on the nearest ligands surrounding of the Mn ions.
The second part of the thesis addresses magnetic properties of nano-scaled magnets such as carbon nanotubes fifilled with magnetic materials and carbon-coated magnetic nanoparticles. These studies are eventually aiming at the possible application of these particles as agents for magnetic hyperthermia. In this respect, their behavior in static and alternating magnetic fifields is investigated and discussed. Moreover, two possible hyperthermia applications of the studied magnetic nanoparticles are presented, which are the combination of a hyperthermia agents with an anticancer drug and the possibility to spatially localize the hyperthermia effffect by applying specially designed static magnetic fifields.
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Henderson, John. "SPIN QUANTUM DYNAMICS IN MOLECULAR MAGNETS." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3535.
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Molecular magnets are ideal systems to probe the realm that borders quantum and classical physics, as well as to study decoherence phenomena in nanoscale systems. The control of the quantum behavior of these materials and their structural characteristics requires synthesis of new complexes with desirable properties which will allow probing of the fundamental aspects of nanoscale physics and quantum information processing. Of particular interest among the magnetic molecular materials are single-molecule magnets (SMMs) and antiferromagnetic (AFM) molecular wheels in which the spin state of the molecule is known to behave quantum mechanically at low temperatures. In previous experiments the dynamics of the magnetic moment of the molecules is governed by incoherent quantum tunneling. Short decoherence times are mainly due to interactions between molecular magnets within the crystal and interactions of the electronic spin with the nuclear spin of neighboring ions within the molecule. This decoherence problem has imposed a limit to the understanding of the molecular spin dynamics and the sources of decoherence in condensed matter systems. Particularly, intermolecular dipolar interactions within the crystal, which shorten the coherence times in concentrated samples, have stymied progress in this direction. Several recent works have reported a direct measurement of the decoherence time in molecular magnets. This has been done by eliminating the dephasing created by dipolar interactions between neighboring molecules. This has been achieved by a) a dilution of the molecules in a liquid solution to decrease the dipolar interaction by separating the molecules, and b) by polarizing the spin bath by applying a high magnetic field at low temperatures. Unfortunately, both approaches restrict the experimental studies of quantum dynamics. For example, the dilution of molecular magnets in liquid solution causes a dispersion of the molecular spin orientation and anisotropy axes, while the large fields required to polarize the spin bath overcome the anisotropy of the molecular spin. In this thesis I have explored two methods to overcome dipolar interactions in molecular magnets: a) studying the dynamics of molecular magnets in single crystals where the separation between magnetic molecules is obtained by chemical doping or where the high crystalline quality allows observations intrinsic to the quantum mechanical nature of the tunneling of the spin, and b) studying the electronic transport through an individual magnetic molecule which has been carefully placed in a single-electron transistor device. I have used EPR microstrip resonators to measure Fe17Ga molecular wheels within single crystals of Fe18 AFM wheels, as well as demonstrating, for the first time in a Single Molecule Magnet, the complete suppression of a Quantum Tunneling of the Magnetization transition forbidden by molecular symmetry.Ph.D.
Department of Physics
Sciences
Physics PhD
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Sun, Fei. "Transformation Optics for Controlling DC Magnetic Field." Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155326.
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Based on the form-invariant of Maxwell’s equations under coordinate transformations, we extend the theoryof transformation optics to transformation magneto-statics, which can design magnets through coordinatetransformations. Some novel DC magnetic field illusions created by magnets (e.g. rescaling magnets,cancelling magnets and overlapping magnets) are designed and verified by numerical simulations. Ourresearch will open a new door to designing magnets and controlling DC magnetic fields.QC 20141105
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Varghese, Philip. "Magnet design considerations for superconductive magnetic energy storage." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-02052007-081238/.
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Melander, Emil. "Optical and magneto-optical diractometer for studies ofpatterned magnets." Thesis, KTH, Tillämpad fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-32898.
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A MOKE setup was constructed and measurements have been performed in order to verify the versatility of this equipment. The quadrupole air core coils are capable of delivering a maximum magnetic eld of 13 mT in longitudinal, transversal as well as polar MOKE. The diractometer enables re ective scans (Kerr eect) from 20 to 90 degrees and transmissive scans (Faraday eect) from 0 to 90 degrees (optical convention). The combined equipment that constitutes of these two parts enables thorough characterization of optical, magnetical and magneto-optical phenomena which will be of great benet for studies of patterned nano-magnets. The setup is designed to reveal the in uence of optical eects coupled to various structures like plasmon resonance and plasmonic band gaps into the magnetic and magneto-optical properties of patterned nanostructures.
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Poole, A. L. "Magnetism in frustrated magnets revealed by neutron polarimetry." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1302402/.
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The work in this thesis uses neutron polarimetry and representational analysis to illuminate complex magnetic structures. The combination of these techniques is particularly suited to examining magnetic materials that have frustrated magnetic order and domain structures. The materials that are investigated in depth are Er2Ti2O7 and MnWO4. Er2Ti2O7 is a member of the pyrochlore family of materials and exhibits the classic signs of geometric frustration. The material has been proposed as an XY antiferromagnet that selects a specic basis vector ground state due to an order-by-disorder transition. The previous experimental work could not fully determine the precise details of the ground state and hence was not able to fully conrm the proposed theory. The structure was examined using neutron polarimetry and representational analysis to try and determine the magnetic order at low temperature. MnWO4 is an example of a magnetic material with complex order and frustration that arises due to competing exchange interactions. The material has a cycloidal magnetic structure that breaks the inversion symmetry and gives rise to dierent k-domains. The population of these dierent domains is intrinsically linked to the electronic polarization of the material, such that when one domain is populated MnWO4 has a spontaneous electric polarization and is belongs to the multiferroic family of materials. By using representation analysis the number of parameters that is required to describe the magnetic structure is greatly reduced and the link between inversion symmetry breaking and multiferroicity may be better understood. This thesis aims to identify the structures of both Er2Ti2O7 and MnWO4 as well as develop the interpretation of the polarimetry techniques.
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Lopez, Gomez Partida Fausto. "Design of a Permanent Magnet Synchronous Generator with Alnico Magnets." Thesis, Uppsala universitet, Elektricitetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-395215.
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Following the trends to diminish the fossil fuel energy production new technologies known for their renewable sources have become a signficant option for helping combat climate change and handle the current oil prices. These new technologies base their power production on already established physical principles that convert mechanical power to electrical power. Generators are the fundamental piece of machinery for electricity production. Among the various types of generators that exist, permanent magnet synchronous generators (PMSGs) are commonly used for renewable electricity production. At present, the most used magnets for PMSGs are alloys of neodymium, iron, and boron which form a tetragonal crystalline structure known as Neodymium magnets (NdFeB). These types of magnets contain rare-earth materials, which makes them highly non-sustainable materials. Research to find new magnet compositions to substitute rare earth magnets or to reduce the weight and increase the efficiency of PMSGs is currently being studied. One option is to use Alnico magnets. This thesis project explores this option. With the help of a finite element analysis (FEA) software (COMSOL Multiphysics), three types of Alnico grades 5, 8 and 9 were implemented in the rotor of a spoke type generator to study the load limits of the rotor magnets, and together with this observe the demagnetization and impact that it has on the power production of the generator, in two different scenarios: 1) When the generator is connected to a nominal load under normal conditions and 2) when the generator is connected to a nominal load after a short circuit (SC). The simulations provided an insight into the load limitations that the generator has by each type of Alnico studied. Alnico 9 showed to be the best candidate magnet from the three magnets implemented with less demagnetization and higher electrical power output, followed by Alnico 8, which presented a good electrical power output at the nominal load scenario. Regardless of the higher demagnetization of Alnico 5, it proved to be a better candidate than Alnico 8 at the SC scenario.
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DAMENTO, MICHAEL ANTHONY. "DETECTION OF MAGNETIZATION REVERSAL IN A NEODYMIUM-IRON-BORON MAGNET USING A HALL-EFFECT MICROPROBE." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183945.
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Magnetization processes in a sintered Nd-Fe-B permanent magnet (NEOMAX-35) were examined on a small scale using a Hall-effect microprobe with an active area 75 μm on a side. Probes were made by evaporating bismuth through a stencil mask onto glass slides. Experiments were performed by placing a probe onto the polished pole face of a Nd-Fe-B magnet and inserting the probe-magnet assembly into an electromagnet. Barkhausen steps, indicating rapid domain wall motion, were observed (superimposed upon the blank probe signal) in the demagnetization of a fully magnetized magnet. Magnetization traces for a thermally demagnetized Nd-Fe-B magnet did not exhibit measurable Barkhausen steps until a field of approximately 1.2 T was applied. The following observations were made for two thermally demagnetized samples which were cycled through minor hysteresis loops (maximum applied field of approximately 2 T): (1) virgin magnetization traces did not contain measurable Barkhausen steps, however all other forward and reverse magnetization traces did; (2) the initial reverse magnetization trace exhibited more and larger Barkhausen steps than subsequent traces; and (3) some Barkhausen steps were repeatable, that is, occurring at approximately the same field on each subsequent forward or reverse trace. Hall voltage signals were on the order of millivolts for probe currents of 10 mA.
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Seabra, Luís Miguel Alves Vidal de. "Novel phases in frustrated magnets under high magnetic field." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535217.
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Luo, Guangpu. "Electron Transport via Single Molecule Magnets with Magnetic Anisotropy." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/87532.
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Single molecule magnets (SMMs) are molecules of mesoscopic scale which exhibit quantum properties such as quantum tunneling of magnetization, quantum interference, spin filtering effects, strong spin-phonon coupling and strong hyperfine Stark effects. These effects allow applications of SMMs to high-density information storage, molecular spintronics, and quantum information science. Therefore, SMMs are of interest to physicists, chemists, and engineers. Recently, experimental fabrication of individual SMMs within transistor set-ups have been achieved, offering a new method to examine magnetic properties of individual SMMs. In this thesis, two types of SMMs, specifically Eu2(C8H8)3 and Ni9Te6(PEt3)8, are theoretically investigated by simulating their electron transport properties within three-terminal transistor set-ups.
An extended metal atom chain (EMAC) consists of a string of metallic atoms with organic ligands surrounding the string. EMACs are an important research field for nanoelectronics. Homometallic iron-based EMACs are especially attractive due to the high spin and large magnetic anisotropy of iron(II). We explore the exchange coupling of iron atoms in two EMACs: [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2].
Chapter 1 provides an introduction to SMMs, electron transport experiments via SMMs and an introduction to density functional theory (DFT).
Chapter 2 presents a theoretical study of electron transport via Eu2(C8H8)3. This type of molecule is interesting since its magnetic anisotropy type changes with oxidation state. The unique magnetic properties lead to spin blockade effects at zero and low bias. In other words, the current through this molecule is completely suppressed until the bias voltage exceeds a certain value.
Chapter 3 discusses a theoretical study of electron transport via Ni9Te6(PEt3)8. The magnetic anisotropy of this magnetic cluster has cubic symmetry, which is higher than most SMMs. With appropriate magnetic anisotropy parameters, in the presence of an external magnetic field, uncommon phenomena such as low-bias blockade effects, negative conductance and discontinuous conductance lines, are observed. In Chapter 2 and 3 DFT-calculated magnetic anisotropy parameters are used and electron transport properties are calculated by solving master equations at low temperature.
Chapter 4 examines the exchange coupling between iron ions in EMACs [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. The exchange coupling constants are calculated by using the least-squares fitting method, based on the DFT-calculated energies from different spin configurations.Ph. D.
Single molecule magnets (SMMs) are molecules of mesoscopic scale which exhibit quantum properties. Its quantum effects are used to describe the behavior of SMMs at the smallest scales. These quantum properties could also be used to reveal possible applications of SMMs to high-density information storage, molecular spintronics, and quantum information science. Thus SMMs are of interest to physicists, chemists, and engineers. Recently, electron transport via individual SMMs was achieved in experiments. Electron transport is obviously affected by the magnetic properties of the SMM, thus one can examine magnetic properties of an SMM indirectly by measuring electron transport via the SMM. In this thesis, two types of SMMs, Eu2(C8H8)3 and Ni9Te6(PEt3)8, are investigated theoretically by simulating their electron transport properties. An extended metal atom chain (EMAC) consists of a string of metallic atoms with organic ligands surrounding the string. EMACs are an important research field for nanoelectronics. Homometallic iron-based EMACs are especially attractive due to the high spin and large magnetic anisotropy of iron(II). If a molecule has magnetic anisotropy, its magnetic properties change with the direction of its magnetic moment. We explore how iron atoms interact with each other in the EMACs [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. Chapter 1 provides an introduction to SMMs, electron transport experiments via SMMs and an approximation method, density functional theory (DFT). DFT is a method to approximate electronic structure and magnetic properties of various many-body systems. Chapter 2 investigates theoretical electron transport via Eu2(C8H8)3. Eu2(C8H8)3 changes its type of magnetic anisotropy when it obtains an extra electron, which is different from most SMMs. If the Eu2(C8H8)3 is short of an extra electron, its magnetization direction is in-plane, that is, its magnetic energy is lowest when its magnetic moment is along any direction in a specific plane. If an extra electron is captured by Eu2(C8H8)3, its magnetization direction becomes out-of-plane, and its lowest energy is obtained when its magnetic moment is along the direction normal to the specific plane. The unique magnetic properties lead to blockade effects at low bias: the current through this molecule is completely suppressed until the bias voltage exceeds a certain value. The bias voltage on a molecule equals the electrical potential difference between two ends of the molecule. Chapter 3 investigates theoretical electron transport via Ni9Te6(PEt3)8. Magnetic anisotropy of Ni9Te6(PEt3)8 is cubic symmetric, and its symmetry is higher than most SMMs. With appropriate magnetic anisotropy parameters, in the presence of an external magnetic field, uncommon phenomena are observed. These phenomena include (1) current is completely suppressed when bias is low; (2) current via SMM decreases while bias on SMM increases; (3) there are discontinuous lines in the figures that describe electrical conductance of current. Chapter 4 examines the iron atoms’ interaction strength in both [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. Reasonable spin Hamiltonians are used to describe the energy of EMACs. Considering all possible directions of the spins of iron atoms in two EMACs, we calculate the energy of every possible spin configuration using DFT. The energy of each spin configuration can be expressed as an equation containing one or more coupling constants. We apply the least-squares fitting method to obtain the values of the coupling constants in the spin Hamiltonians.
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Pejaković, Dusan. "Optical control of magnetic order in molecule-based magnets." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343232538.
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Pejakovi?, Dušan. "Optical control of magnetic order in molecule-based magnets /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486572165278271.
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Khelfallah, Malika. "Magnetic properties of ferrofluids of self-assembled nano-magnets." Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS502.
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Cette thèse a pour objectif principal d'explorer les effets de l’assemblage créé par les interactions magnétiques dipolaires entre des nanoparticules magnétiques en suspension colloïdales dans un liquide (ferrofluide) sur les propriétés magnétiques de ce ferrofluide. Ce travail se base sur la caractérisation approfondie de ferrofluides constitués de nanoparticules en forme de fleurs composées de matériaux magnétiques durs tels que la ferrite de cobalt (CoFe2O4), ou de matériaux magnétiques mous comme la ferrite de manganèse (MnFe2O4) et la maghémite (γ-Fe2O3). Les propriétés magnétiques de ces ferrofluides ont été mesurées à l'aide de magnétométrie classique, mettant en évidence l'influence significative de la composition chimique des nanoparticules sur les caractéristiques macroscopiques du ferrofluide. De plus, je me suis intéressée à la structuration des nanoparticules dans le ferrofluide liquide, en observant des particules isolées ainsi que la formation d'assemblages et d'agrégats, grâce à une méthode de Microscopie Electronique en Transmission cryogénique, avec un protocole développé spécifiquement pendant la thèse. L'impact de la morphologie des nanoparticules sur leurs propriétés magnétiques a été exploré grâce à la tomographie, imagerie en trois dimensions des nanoparticules, en collaboration avec le laboratoire IPCMS de Strasbourg. À l'échelle nanométrique, les propriétés magnétiques des assemblages ont été mesurées au moyen de l'holographie électronique, en collaboration avec le laboratoire CEMES de Toulouse. L'introduction des ferrofluides binaires, définis comme des mélanges de ferrofluides composés de nanoparticules de matériaux magnétiques durs et mous, a permis d'explorer de nouvelles interactions magnétiques dipolaires. Ces matériaux permettent de créer des ferrofluides aux propriétés nouvelles pouvant présenter un intérêt pour des applications biomédicales. Ces ferrofluides binaires ont révélé des propriétés magnétiques globales originales qui diffèrent de la simple addition des propriétés individuelles des ferrofluides originels. En outre, l'organisation des nanoparticules dans le ferrofluide binaire a été minutieusement étudiée en utilisant la spectroscopie chimiquement sélective et résolue spatialement par microscopie à rayons X en transmission sur la ligne HERMES du synchrotron SOLEIL, permettant d'obtenir des cartographies chimiques d’assemblages de nanoparticules de CoFe2O4 et de MnFe2O4. La séparation des contributions magnétiques des deux types de nanoparticules composant le ferrofluide binaire a été réalisée à l'aide d’une technique de magnétométrie appelée diagramme de FORC (First Order Reversal Curve), en collaboration avec le laboratoire IPGP. Les diagrammes de FORC ont permis d’identifier et d’évaluer l’influence des nanoparticules de CoFe2O4 sur le comportement magnétique des nanoparticules de MnFe2O4 dans le ferrofluide binaire. De plus, des mesures de courbes d’aimantation chimiquement sélective par spectroscopie ont été réalisées grâce à une cellule liquide permettant une mesure in-situ des ferrofluides, avec des expériences menées sur la ligne GALAXIES du synchrotron SOLEIL. Enfin, une comparaison des propriétés magnétiques de différents ferrofluides binaires a été entreprise, en variant le ratio entre matériau magnétique dur et mou, la composition du matériau mou ainsi que la taille des nanoparticules, offrant ainsi une perspective complète sur les possibilités de conception et d'optimisation de ces matériaux magnétiques avancés. Cette thèse établit une relation significative entre la structuration des nanoparticules dans le ferrofluide et leurs propriétés magnétiquesThe main objective of this thesis is to explore the effects of the assembly caused by dipolar magnetic interactions between magnetic nanoparticles suspended in a liquid (so-called ferrofluid) on the magnetic properties of this ferrofluid. It is based on the in-depth characterization of ferrofluids made up of flower-shaped nanoparticles composed of hard magnetic materials such as cobalt ferrite (CoFe2O4), or soft magnetic materials such as manganese ferrite (MnFe2O4) and maghemite (γ- Fe2O3). The magnetic properties of these ferrofluids were measured using standard magnetometry methods, highlighting the significant influence of the chemical composition of the nanoparticles on the macroscopic characteristics of the ferrofluid. In addition, this research focused on the structuring of nanoparticles in liquid ferrofluid, by observing isolated particles, as well as the formation of assemblies and aggregates, using a cryogenic Transmission Electron Microscopy method, with a protocol developed specifically during the thesis. The impact of nanoparticle morphology on their magnetic properties was explored using tomography, three-dimensional imaging of nanoparticles, in collaboration with the IPCMS laboratory in Strasbourg. At the nanoscale, the magnetic properties of the assemblies were measured using electron holography, in collaboration with the CEMES laboratory in Toulouse. The study of binary ferrofluids, defined as ferrofluid mixtures composed of nanoparticles of hard and soft magnetic materials, has enabled new dipolar magnetic interactions to be explored. These new materials allow creating ferrofluids with novel properties that may be of interest for biomedical applications. These binary ferrofluids have revealed original bulk magnetic properties that differ from the simple addition of the individual properties of the original ferrofluids. In addition, the organization of nanoparticles in the binary ferrofluid has been meticulously studied using chemically selective and spatially resolved transmission X-ray microscopy on the HERMES beamline at the SOLEIL synchrotron, yielding chemical mappings of CoFe2O4 and MnFe2O4 nanoparticle assemblies. The separation of the magnetic contributions of the two types of nanoparticles composing the binary ferrofluid was achieved using a magnetometry technique known as the FORC (First Order Reversal Curve) diagram, in collaboration with the IPGP laboratory. FORC diagrams were used to assess the influence of CoFe2O4 nanoparticles on the magnetic behavior of MnFe2O4 nanoparticles in the binary ferrofluid. In addition, spectroscopic measurements of chemically selective magnetization curves were carried out using a liquid cell for in-situ ferrofluid measurements, with experiments carried out on the GALAXIES beamline at the SOLEIL synchrotron. Finally, a comparison of the magnetic properties of different binary ferrofluids was undertaken, by varying the ratio between hard and soft magnetic components, the composition of the soft material as well as the size of the nanoparticles, thus providing a comprehensive perspective on the design and optimization possibilities of these advanced magnetic materials. This thesis establishes a significant relationship between the structuring of nanoparticles in ferrofluid and their magnetic properties
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Aubin, Sheila Marie Josée. "Single-molecule magnets /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9820882.
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Schoerling, Daniel. "Superconducting wiggler magnets for beam-emittance damping rings." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2012. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-85819.
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Elektronen- und Positronenstrahlen mit niedrigsten Emittanzen und hohen Strömen werden in zukünftigen Linearbeschleunigern, wie zum Beispiel dem Compact Linear Collider (CLIC), benötigt, um die geforderte Leuchtkraft für physikalische Experimente bereit zu stellen. Diese Strahlen können in Dämpfungsringen, ausgestattet mit starken, supraleitenden Dämpfungswigglermagneten, erzeugt werden. In dieser Arbeit sind Designkonzepte verschiedener supraleitender Dämpfungswigglermagnete entwickelt worden. Testspulen sowie Modelle sind gebaut und getestet, elektrische Verbindungstechniken entwickelt worden. Eine Wärmelastrechnung für den Betrieb in Dämpfungsringen und ein Designkonzept für den kryogenen Betrieb bei 4.2 K ist erstellt worden. Es konnte theoretisch und experimentell gezeigt werden, dass supraleitende Dämpfungswigglermagnete mit Nb-Ti und Nb3Sn Niedertemperatursupraleitern die magnetischen, mechanischen, elektrischen und thermischen Anforderungen erfüllen und in Dämpfungsringen betrieben werden können.
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Inglis, Ross. "Oxime based manganese molecular magnets." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4755.
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The synthesis and characterisation of a large family of hexametallic [MnIII 6] Single-Molecule Magnets with general formula [MnIII 6O2(R-sao)6(X)2(L)4-6] (where sao2- = dianion of salicylaldoxime; R = H, Me, Et, Ph; X = O2CR' (R' = H, Me, Ph etc), Hal , O2PHPh or O2P(Ph)2; L = solvent) are presented. Deliberate structural distortions of the [Mn3O] trinuclear moieties within the complexes are used to tune the observed magnetic properties. These findings highlight a qualitative magnetostructural correlation whereby the type (anti- or ferromagentic) of each Mn2 pairwise magnetic exchange is dominated by the magnitude of each individual Mn-N-O-Mn torsion angle. To shed further light on this intriguing family of nanomagnets, a large family of the analogous “half” molecules has been synthesised and fully characterised. These trimetallic [MnIII 3] complexes can be divided into three categories with general formulae (type 1) [MnIII 3O(R-sao)3(X)(sol)3-4] (where R = H, Me, tBu; X = O2CR (R = H, Me, Ph etc); sol = py and / or H2O), (type 2) [MnIII 3O(R-sao)3(X)(sol)3-5] (where R = Me, Et, Ph, tBu; X = O2CR (R = H, Me, Ph etc); sol = MeOH, EtOH and / or H2O), and (type 3) [MnIII 3O(R-sao)3(sol)3](XO4) (where R = H, Et, Ph, Naphth; sol = py, MeOH, -pic, Et-py, tBu-py; X = Cl, Re). In the crystals the ferromagnetic triangles are involved in extensive inter-molecular H-bonding which is clearly manifested in the magnetic behaviour, producing exchange-biased SMMs. These interactions can be removed by ligand replacement to give “simpler” SMMs. The [MnIII 6] and [MnIII 3] molecular nanomagnets are then exploited as building blocks to construct supramolecular architectures by means of host-guest interactions and coordination driven self-assembly. A number of discrete and infinite architectures based on the molecular triangle [Mn3] and various pyridyl-type ligands were obtained and structurally and magnetically characterised.
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Lim, Joshua A. "The role of local versus itinerant magnetism : studies of dilute magnetic semiconductors and multi-k magnets." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4639/.
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The electronic properties of the materials studied in this thesis: a dilute magnetic semiconductor and a member of the actinide family, are thought to lie on the edge of local and itinerant behaviours. The role of localised versus itinerant magnetism is indirectly explored by characterising the magnetism through a range of experimental techniques. Reports of magnetism in dilute magnetic semiconductors have been largely conflicting, with most focusing on thin films. This work characterises high quality bulk single crystals of Cr-doped TiO\(_2\) and finds no magnetic ordering down to 4K. This suggests that the observed thin film magnetisation is a result of non-equilibrium or impurity phases and lattice strains. In the canonical 3-k magnet, USb, the spin waves soften at a temperature, T* (well below T\(_n\)), with no change in magnetic or structural symmetries. It had been suggested that this was due to de-phasing of the different Fourier components making up the 3-k state: this was tested using inelastic polarised neutrons and found not to be the case. Instead, the effects at T* are likely linked to a change in itinerancy. The magnetic domain dynamics are probed using X-ray photon correlation spectroscopy and find changes to the domains near T\(_n\) and also T*.
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Hilton, Geoffrey. "The analysis of magnetic drives using rare earth permanent magnets." Thesis, University of Sunderland, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368123.
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Pollard, Robert James. "The microstructure and magnetic properties of NdFeB based permanent magnets." Thesis, University of Salford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328260.
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Brunt, Daniel C. "Magnetic properties of frustrated Shastry-Sutherland magnets : rare earth tetraborides." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/98779/.
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Geometrically frustrated magnetism arises when the competing interactions are incompatible with the geometry of the lattice. This leads to a large ground state degeneracy and the system typically has difficulty establishing a unique ground state, often giving rise complex intermediate magnetic phases and other unusual phenomena. Recently the rare-earth tetraborides, RB4, family of compounds has garnered attention as it is a rare experimental realisation of the frustrated Shastry-Sutherland lattice. Here the R3+ ions form a network of squares and triangles which is topologically equivalent to the Shastry-Sutherland lattice. The competing interactions leads to a rich variety of magnetic phase in the RB4 family in both zero and applied magnetic field. An investigation into two members of the RB4 family, HoB4 and NdB4 is presented in this thesis. Both compounds show successive magnetic phase transitions, where HoB4 orders with an incommensurate magnetic state at 7.1 K and orders with a non-collinear antiferromagnetic structure at 5.7 K, as well as magnetisation plateaux with fractional values of the saturation magnetisation of 1/6,1/3 and 5/3. NdB4 orders at 17 K with a non-collinear antiferromagnetic structure followed by two distinct incommensurate structures at 7 K and 4.9 K. NdB4 shows a single magnetisation plateau at 1/5 the saturation magnetisation. Bulk property measurements of magnetisation, magnetic susceptibility, resistivity and heat capacity were used to maps out and construct the complex phase diagrams of HoB4 and NdB4 with measurements down to 0.5 K and magnetic fields up to 500 kOe. HoB4 shows six distinct magnetic phases, while NdB4 has five The stabilised magnetic phases were determined in zero field using single crystal neutron diffraction measurements utilising both polarised and un-polarised measurements. While the un-polarised neutron measurements were extended to investigate the magnetic structures of the field-induced magnetic structure in both HoB4 and NdB4. Finally inelastic neutron scattering measurements on polycrystalline samples were used to map out the crystal field scheme in HoB4 and NdB4. Single crystal samples were used to investigated the low temperature magnetic excitations in HoB4. The initial analysis of the inelastic neutron studies is presented. Overall, both HoB4 and NdB4 exhibit a variety of magnetic phenomena, and their magnetic properties contribute to the understanding of the physics of the RB4 family of compounds.
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Venkateswaran, N. "Magnetic and microstructure properties of iron-rare earth-carbon magnets." Thesis, Kansas State University, 1988. http://hdl.handle.net/2097/16051.
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Tituana, Luis Rodrigo. "IMPLEMENTATION OF A PLANAR MAGNETIC MANIPULATOR WITH ROTATABLE PERMANENT MAGNETS." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/theses/2664.
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The development of new techniques for control of magnetic objects by external magnetic fields has been in constant improvement. These advancements range from the design and fabrication of magnetic nanoparticles to design and control of actuators that enable their manipulation. The ability to guide such magnetic objects at a distance without any direct mechanical contact is an attractive feature with great potential in medical applications. Magnetic fields are not distorted by their interaction with nonmagnetic materials, like those in the human body; and pose no harm to living tissues, which make them convenient tools for minimally invasive techniques and treatments. Moreover, several actuator configurations have been proposed to achieve the remote motion of a magnetic particle or magnetic fluids. Arrays of electromagnets have been widely utilized due to their lack of mechanical parts and flexibility to accurately and rapidly change their magnetic field by controlling the current through their coils. However, they are relatively weak for their size and electrical power, making them inefficient for medical applications which need large magnetic forces at relatively long distances. On the other hand, permanent magnets have a much higher strength-to-size ratio than electromagnets and allow for control from larger distances. The disadvantage is that their magnetic fields cannot be turned off and a mechanical actuator is needed to modify their position and orientation to change their field. In this work, a magnetic manipulator used as a testbed to manipulate a magnetic bead is designed. It consists of an array of six diametrically magnetized cylindrical permanent magnets evenly spaced around a petri dish, following the work in [11]. Servomotors are utilized to precisely adjust the direction of the magnets according to a control law developed by other researchers in the past. A monochromatic camera located above the petri dish provides the feedback on the position of the bead and a set of hall-effect sensors provides the location of the poles of the magnets. The dynamics of the system is modeled by a linearized set of state-space equations where the magnetic field is estimated with an analytical expression for the geometry of the magnets. The testbed has been designed with the CAD software SolidWorks and its structure has been completely 3D printed with polylactic acid (PLA) filament. The design is tested under different speeds of the servomotors and initial orientations of the magnets. Some recommendations are presented at the end for improvement and considerations for future designs.
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Gîrtu, Mihai A. "Magnetic ordering in hybrid organic/inorganic nanocomposites -magnets by design-." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343145729.
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Gîr?u, Mihai A. "Magnetic ordering in hybrid organic/inorganic nanocomposites -magnets by design- /." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487949836207972.
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Borghi, Chiara Caterina <1986>. "Continuous-Flow Magnetic Separation with Permanent Magnets for Water Treatment." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6233/1/Borghi_ChiaraCaterina_tesi.pdf.
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More efficient water treatment technologies would decrease the water bodies’ pollution and the actual intake of water resource. The aim of this thesis is an in-depth analysis of the magnetic separation of pollutants from water by means of a continuous-flow magnetic filter subjected to a field gradient produced by permanent magnets. This technique has the potential to improve times and efficiencies of both urban wastewater treatment plants and drinking water treatment plants. It might also substitute industrial wastewater treatments. This technique combines a physico-chemical phase of adsorption and a magnetic phase of filtration, having the potential to bond magnetite with any conventional adsorbent powder. The removal of both Magnetic Activated Carbons (MACs) and zeolite-magnetite mix with the addition of a coagulant was investigated. Adsorption tests of different pollutants (surfactants, endocrine disruptors, Fe(III), Mn(II), Ca(II)) on these adsorbents were also performed achieving good results. The numerical results concerning the adsorbent removals well reproduced the experimental ones obtained from two different experimental setups. In real situations the treatable flow rates are up to 90 m3/h (2000 m3/d).
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Borghi, Chiara Caterina <1986>. "Continuous-Flow Magnetic Separation with Permanent Magnets for Water Treatment." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6233/.
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More efficient water treatment technologies would decrease the water bodies’ pollution and the actual intake of water resource. The aim of this thesis is an in-depth analysis of the magnetic separation of pollutants from water by means of a continuous-flow magnetic filter subjected to a field gradient produced by permanent magnets. This technique has the potential to improve times and efficiencies of both urban wastewater treatment plants and drinking water treatment plants. It might also substitute industrial wastewater treatments. This technique combines a physico-chemical phase of adsorption and a magnetic phase of filtration, having the potential to bond magnetite with any conventional adsorbent powder. The removal of both Magnetic Activated Carbons (MACs) and zeolite-magnetite mix with the addition of a coagulant was investigated. Adsorption tests of different pollutants (surfactants, endocrine disruptors, Fe(III), Mn(II), Ca(II)) on these adsorbents were also performed achieving good results. The numerical results concerning the adsorbent removals well reproduced the experimental ones obtained from two different experimental setups. In real situations the treatable flow rates are up to 90 m3/h (2000 m3/d).
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Peil, Oleg E. "Theory of Disordered Magnets." Doctoral thesis, Uppsala universitet, Institutionen för fysik och materialvetenskap, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9528.
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Studying magnetic properties of disordered alloys is important both for the understanding of phase transformations in alloys and from the point of view of fundamental issues of magnetism in solids. Disorder in a magnetic system can result in unconventional magnetic structures, such as spin glass, which have rather peculiar features. In this Thesis, a rather general approach to studying disordered magnetic alloys from first principles is presented. Phase transformations and magnetic behavior of crystalline substitutional alloys are considered. This approach is exemplified by calculations of an archetypical spin-glass material: the CuMn alloy. First, a general theoretical framework for the description of the thermodynamics of disordered magnetic alloys is given. It is shown that under certain conditions, a complex magnetic system can be reduced to an effective system containing no magnetic degrees of freedom. This substantially simplifies the investigation of phase transformations in magnetic alloys. The effective model is described in terms of material-specific interaction parameters. It is shown that interaction parameters can be obtained from the ground-state property of a disordered alloy which are in turn calculated from first principles by means of highly accurate up-to-date numerical techniques based on the Green's function method. The interaction parameters can subsequently be used in thermodynamic Monte-Carlo simulations to produce the atomic and magnetic structures of an alloy. An example of calculations for the Cu-rich CuMn alloy is given. It is demonstrated that the atomic and magnetic structure of the alloy obtained by the presented approach agrees very well with the results of neutron-scattering experiments for this system. Moreover, numerical simulations enable one to predict the ground state structure of the alloy, which is difficult to observe in experiment due to large atomic diffusion barriers at temperatures close to the temperature of the phase transformation. A general description of a spin glass is given, and difficulties of modeling this type of magnetic systems are discussed. To overcome the difficulties, improved Monte-Carlo methods, such as parallel tempering, overrelaxation technique, and finite-size scaling method of analysis, are introduced. The results for the CuMn alloy are presented.
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Mohan, Ashwin. "Low-Dimensional Quantum Magnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-155389.
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The field of low-dimensional quantum magnets has received lot of attention owing to the possibility of studying phenomena associated with the quantum nature of matter. Many materials that realize low-dimensional spin arrangements in their structure have been synthesized in the past twenty years due to the emergence and development of crystal growth techniques. These materials have been studied using various experiments in order to explore the wide range of interesting properties predicted theoretically for low-dimensional systems. In this pursuit, novel properties have been observed and many open questions have been raised. One such property that is typically observed in many low-dimensional quantum magnets is heat transport via magnetic excitations.
Large magnitudes of magnetic heat conductivity has been found experimentally in materials belonging to this class in addition to the conventionally known phononic heat conduction, and interesting theoretical predictions like the divergence of heat conductivity in certain spin models exist, that have stimulated research in this field.
This experimental work mainly deals with the crystal growth and heat transport properties of low-dimensional quantum magnets that include one-dimensional (1D) spin chain systems Sr$_2$CuO$_3$ and SrCuO$_2$, two-dimensional (2D) Heisenberg antiferromagnet La$_2$CuO$_4$, and a five-leg spin ladder La$_8$Cu$_7$O$_{19}$, with a view to understand propagating low-energy magnetic excitations and their interaction amongst themselves, other quasiparticles and impurities present in the systems. These interactions result in scattering processes that govern the magnitude and temperature dependence of heat conductivity. In spite of considerable theoretical and experimental work in the field of heat transport, a complete understanding of the scattering mechanisms is lacking. The work tries to add to the experimental knowledge about magnetic heat transport in such systems and presents cases which motivate the need for theoretical understanding of aspects of heat transport.
The focus of this work was twofold. One part focusses on the single crystal growth using the travelling-solvent floating zone (TFSZ) method of materials which realize low-dimensional spin systems in their structure. The TFSZ method is indispensable for growing large single crystals of extraordinary purity, which can be used for investigations using neutrons and other techniques like heat conductivity measurements that probe anisotropic properties. The other part deals with the experimental results on heat transport and other thermodynamic properties of these materials.
In order to study the behaviour of the magnetic heat conductivity at high temperatures, and the effect of small amount of magnetic and non-magnetic impurities on the heat transport of 2D Heisenberg antiferromagnet La$_2$CuO$_4$, single crystals of pure La$_2$CuO$_4$, and Ni- and Zn-doped versions, La$_2$Cu$_x$Ni$_{1-x}$O$_4$ and La$_2$Cu$_x$Zn$_{1-x}$O$_4$ for $x$ = 0.001 and 0.003, were grown using the TFSZ method. Heat transport in the pure compound was experimentally investigated for the first time up to very high temperatures of 813 K using two methods, namely the steady state method for low temperatures and the dynamic flash method for measuring high temperature conductivity. Analysis of the magnon mean-free path using empirical models based on semi-classical theories, and qualitative comparison to theoretical calculations seems to suggest that scattering between magnons might play an important role in addition to scattering of magnons with phonons and defects, and that the spin-spin correlation length could be crucial in limiting the mean free path of magnons at high temperatures. These experimental results and indications of probable scattering mechanisms based on non-rigorous analyses and comparisons, strongly motivate the need for theoretical studies. Heat conductivity measurements on the Ni- and Zn- doped versions of La$_2$CuO$_4$ are still incomplete and inconclusive, and hence have not been reported in this work.
Heat transport experiments on Ni- and Ca-doped Sr$_2$CuO$_3$ were performed, with a motivation to investigate the role of disorder induced by impurities lying within the spin chains (Ni) and those lying outside the spin chains (Ca), on the heat transport in this system. In both the cases, the magnetic heat transport is observed to be strongly suppressed upon doping. Empirical analysis of the data seems to suggest that in the temperature regime of 100-300 K, the temperature dependence of the mean-free path of magnetic excitations for the Ni- and Ca-doped samples can be described by scattering with defects (Ni and Ca impurities) and phonons alone.
However, surprisingly, a strong increase of phononic conductivity is observed perpendicular and parallel to the spin chains of the Ni-doped compounds compared to the pure compounds, whose explanation seems to lie in the existence of an additional dissipative scattering mechanism present in the pure compounds that is lifted upon doping, possibly due to the presence of a spin gap in the doped compounds. The effect of Ni on the Sr$_2$CuO$_3$ and SrCuO$_2$ was also investigated by studying the low energy regime of the spin excitation spectrum using other microscopic probes like nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS). Large single crystals of SrCu$_x$Ni$_{1-x}$O$_2$, with $x$ = 0.01 were grown and used in these experiments that observed the presence of a spin gap in the Ni-doped sample. Further theoretical investigations are however required to understand the possible role of the spin gap in influencing the spin-phonon scattering mechanism, and its relevance to the observed enhancement in phononic conduction.
Although we observe that in the case of both 1D and 2D systems, a semi-classical kinetic model for heat transport along with empirical models of scattering processes describe the temperature dependence of the measured heat conductivity surprisingly well in the temperature regime up to 300 K and 800 K respectively, interpretations based on these analyses must be treated as only preliminary, and as a step towards understanding microscopically the scattering mechanisms involved in low-dimensional systems such as the ones discussed in this work.
In the direction of exploratory research towards synthesis of novel low-dimensional materials, two cuprate compounds were synthesized in the form of single crystals using the floating zone method for the first time, namely, a five leg $S=tfrac{1}{2}$ antiferromagnetic spin ladder compound La$_8$Cu$_7$O$_{19}$ and an insulating delafossite LaCuO$_{2}$. A bulk 3D antiferromagnetic ordering is observed in La$_8$Cu$_7$O$_{19}$. Heat conductivity of La$_8$Cu$_7$O$_{19}$ is observed to be purely phononic and no contribution from magnetic excitations seem to exist, although the measurements indicates that there is a large anisotropy in heat transport. However, detailed diffraction experiments using x-rays and neutrons indicate that both the crystal and magnetic structures are complicated, and that the details of the structure prevent La$_8$Cu$_7$O$_{19}$ from being a perfect realization of a five-leg spin ladder.
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NikoliÄ, Predrag 1974. "Geometrically frustrated quantum magnets." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28650.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.Includes bibliographical references (p. 215-219).
(cont.) more general lessons on frustrated quantum magnetism. At the end, we demonstrate some new mathematical tools on two other frustrated two-dimensional systems, and summarize our conclusions, with an outlook to remaining open problems.
In this thesis we attempt to reach a physical understanding and theoretical description of some of the greatest challenges in the field of frustrated quantum magnetism, mainly the Kagome lattice antiferromagnets. After an introductory review of concepts, we closely examine the Kagome lattice quantum Heisenberg and Ising models. We apply several new techniques based on lattice gauge theories, duality mappings and field theory in order to explore phase diagrams of these models. Our approach provides a microscopic picture of the mysterious phenomena observed numerically and experimentally in the Kagome Heisenberg antiferromagnets. Namely, we argue that the spinless excitations, thought to be gapless in absence of any symmetry breaking in this system, are in fact gapped, but at an extremely small emergent energy scale. This scenario is realized in an unconventional valence-bond ordered phase, with a very large unit-cell and complex structure. We also discuss properties of a spin liquid that could be realized in the Kagome antiferromagnet, and argue that its elementary excitations are clearly gapped and extremely massive or even localized. We demonstrate that the Kagome lattice quantum Ising models are an excellent platform for learning about effects of quantum fluctuations on classically degenerate ground-states. We consider several ways in which spins can acquire quantum dynamics, including transverse field, XXZ exchange and ring-exchange perturbations. Using two different setups of compact U(1) gauge theory we find circumstances in which many characteristic quantum phases occur: disordered phase, topologically ordered spin liquid, valence-bond crystal, and a phase with coexistence of magnetic and valence-bond order. From this variety of results we attempt
by Predrag NikoliÄ.
Ph.D.
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Morin, Brian Gerald. "Disorder in molecular magnets." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343230971.
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Farr, Matthew. "Production of anisotropic injection moulded NdFeB magnets from end-of-life sintered magnets." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8116/.
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In this work, the hydrogenation-disproportionation-desorption-recombination (HDDR) processing conditions were optimised for scrap sintered NdFeB magnets from hard disk drives (HDDs). The HDDR process was then performed on scrap sintered NdFeB magnets, which were separated from HDD assemblies using hydrogen, on a large scale in order to produce anisotropic NdFeB alloy powder. The HDDR powder was then used to produce injection moulded magnets on pilot scale equipment (5 kg load) at Kolektor Magnet Technology GmbH, Germany. Sintered NdFeB magnets were separated from cropped hard disk drive corners as a hydrogenated powder, before being purified to remove any contaminants. The material was then HDDR processed using parameters optimised for this material (900 °C and 1200 mbar). The powder was compounded with polyamide 12 at a 90/10 ratio of HDDR powder to binder before injection moulding in a 500 mT field to form bonded magnets. The best bonded magnets produced had a remanence of 0.64 T, a coercivity of 623 kA/m and a BHmax of 61.7kJ/m\(^3\). Despite the mixed composition input feed, there was very little variation in the magnetic properties between 5 randomly selected magnets where a standard deviation for BHmax of 0.34 kJ/m\(^3\) was observed.
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De, Silvestri Federica. "Investigation of the magnetic levitation between HTS bulks and permanent magnets." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Lo scopo di questa ricerca è lo studio della levitazione magnetica risultante dall'interazione fra bulk di superconduttori ad alta temperatura critica e magneti permanenti. E' stato realizzato un modello numerico 2D in Comsol che simula l'interazione fra i due componenti, per studiare la forza di levitazione ottenuta. Il modello è stato successivamente validato con i risultati sperimentali ottenuti nei laboratori del dipartimento di Ingegneria dell'Energia Elettrica dell'Università di Bologna, ottenendo un buon riscontro sia per quanto riguarda i valori della forza sia per quanto riguarda le distribuzioni di campo e di corrente.
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Schneider, Claus M., Daniel E. Bürgler, Peter M. Oppeneer, Vancho Kocevski, Shigeo Arai, Roman Adam, Kazuyoshi Tatsumi, Ján Rusz, and Shunsuke Muto. "Quantitative characterization of nanoscale polycrystalline magnets with electron magnetic circular dichroism." nature publishing group, 2014. http://hdl.handle.net/2237/20835.
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Dudáš, Juraj. "Návrh synchronního motoru s vnějším rotorem a s permanentními magnety." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221153.
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The diplomatic thesis will describe the principle functions of synchronous motors with permanent magnets, for therein analysis of PMSM and BLDC motors. We will make calculation of the required parameters from the power unit for glider Discus 2. We will create a design of BLDC and PMSM motor from specified parameters. Features of the proposed engines will be verified with the help of the programs FEMM, RMxprt, Maxwell. At the end of the work will make conclusion about the diplamatic project and diffrences between PMSM and BLDC motor.
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Chen, Hansheng. "Correlating the microstructure, magnetic domain structure, and magnetic properties of rare earth permanent magnets." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/18996.
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Rare earth permanent magnets have been broadly integrated into various applications, such as advanced electric motor technologies which partly relieve the current energy crisis worldwide by taking advantages of their extraordinary magnetic properties. Traditional approaches for increasing the intrinsic coercivity (Hci) of rare earth permanent magnets typically come at the expense of remanence, resulting in a reduction of maximum magnetic energy product [(BH)max]. Therefore, novel design and processing strategies are in urgent need to circumvent this trade-off in the advanced rare earth permanent magnets. It is well known that the Hci and (BH)max of rare earth permanent magnets can be improved via tuning their microstructure/microchemistry at the nanoscale. Furthermore, the understanding and controlling the magnetic reversal process is equivalently essential in developing high-performance rare earth permanent magnets, since the magnetic domain structure determines the magnetic properties intrinsically. It is therefore of utmost importance to understand the correlation among microstructure, magnetic domain structure, and magnetic properties of rare earth permanent magnets. The thesis consists of three major topics, which are (i) strip cast Nd-Fe-B flake; (ii) sintered Nd-Fe-B magnet, (iii) sintered Sm2Co17 type magnet. To fully understand the effects of microstructure/composition on magnetic domain structure and magnetic properties of these rare earth permanent magnets, we investigated the effects of different heat treatment approaches on magnetic structure and magnetic properties of the aforementioned rare earth permanent magnets by integrating multiple cutting-edge microscopic techniques, including scanning electron microscopy, energy dispersive x-ray spectroscopy, electron backscatter diffraction, focused ion beam, transmission electron microscopy, magnetic force microscopy and atom probe tomography, in conjunction with micromagnetic simulations.
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Castaldi, Lorenzo. "Thin film rare earth magnets." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289666.
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Dakin, Simon John. "Spin fluctuations in metallic magnets." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359234.
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Sidambe, Alfred Twala. "Surface engineered polymer bonded magnets." Thesis, Cranfield University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427154.
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Head, David Ian. "Two dimensional Langmuir-Blodgett magnets." Thesis, University of Southampton, 1988. https://eprints.soton.ac.uk/192469/.
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The susceptibility of quasi-two-dimensional magnets formed by the Langmuir-Blodgett deposition of manganese stearate on aluminium foil has been measured at several points between 20 K and 0.4 K. Large area samples of 101 and 11 layers were detected by a SQUID magnetometer. With the magnetic field parallel to the film we deduced an equivalent volume susceptibility of 6.4x10(-3) at 4.2 K. The signals from the multilayers were paramagnetic in nature and no evidence for a transition was found. Unfortunately the signal from a bilayer and monolayer were masked by contaminants on the substrate. The magnetometer used a cold finger to which the sample was attached. This was then moved into the pick-up coil, which was a second order gradiometer capable of cancelling out the signal from the long (150 mm) substrates. The magnetometer was usefully capable of detecting a sample with a moment down to 5x10(-11) Am(2) but vibration noise restricted the magnetic field to below 10 mT, New equations were developed to describe the magnetic signals from a cylindrical magnetised sample within a superconducting shield. They were developed for use on a micro-computer making it possible to simulate the signal from the sample. The tt-A curves for Manganese stearate were also studied. The uncertainty in the measurement of tx using filter papers was studied and estimated to be 2%. The manganese stearate was observed to transfer by Y and forced-Z type dipping.
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Nicolas, Léa. "Modélisation mathématique des spring magnets." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX051.
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Cette thèse est consacrée à l'étude de matériaux nanocomposites, qui sont l'approche la plus prometteuse et la plus active pour fabriquer les meilleurs aimants permanents actuellement. Ce type d'aimant est appelé spring magnet.Mathématiquement parlant, l'étude de ces matériaux est difficilecar les modèles habituels sont non linéaires et la dépendance matérielle deles paramètres varient à une très petite échelle. Ainsi, résoudre directement les modèles magnétiques pour ces aimants est irréalisable, car les faibles dimensions des matériaux augmenteraient le nombre de cellules dans le maillage de manière prohibitive. Un moyen plus pratique est de dériver un modèle macroscopique en utilisant des techniques d'homogénéisation, ce qui désigné un ensemble de méthodes de moyennisation dans les équations aux dérivées partielles. En d'autres termes, l'homogénéisation cherche des paramètres effectifs (aussi appelés homogénéisés, ou macroscopiques) pour décrire des milieux désordonnés ou très hétérogènes.La thèse consiste en quatre chapitres, dont le premier introduit le cadre de notre étude, et les trois suivants sont en grande partie indépendants. Nous étudions dans le second chapitre l'homogénéisation stochastique de l'équation de Landau-Lifschitz-Gilbert, qui décrit l'évolution temporelle de l'aimantation dans un continuum ferromagnétique, afin d'obtenir un modèle homogène pour les spring magnets, à partir d'un modèle hétérogène. Une fois ce modèle homogène identifié, nous étudions dans le troisième chapitre le comportement d'un aimant permanent homogène, mais non uniforme, via la résolution d'un problème aux valeurs propres. Enfin, le quatrième chapitre s'intéresse au calcul numérique des coefficients homogénéisés, qui nécessite la résolution d'une équation aux dérivées partielles. Nous explorons dans ce chapitre une méthode utilisant des éléments finis, ainsi que des méthodes multi-grillesThis thesis is dedicated to the study of nanocomposite materials, which are the most promising and active approach to making the best permanent magnets today. This type of magnet is called a spring magnet.Mathematically speaking, the study of these materials is difficult.because the usual models are non-linear and the material dependence ofthe parameters vary on a very small scale. Thus, solving the magnetic models for these magnets directly is impractical, as the small dimensions of the materials would increase the number of cells in the mesh prohibitively. A more practical way is to derive a macroscopic model using homogenization techniques, which refers to a set of averaging methods in partial differential equations. In other words, homogenization searchs for effective parameters (also called homogenized, or macroscopic) to describe disordered or highly heterogeneous media.The thesis consists of four chapters, the first of which introduces the framework of our study, and the next three are largely independent. In the second chapter, we study the stochastic homogenization of the Landau-Lifschitz-Gilbert equation, which describes the temporal evolution of magnetization in a ferromagnetic continuum, in order to obtain a homogeneous model for spring magnets, from a heterogeneous model. Once this homogeneous model has been identified, we study in the third chapter the behaviour of a homogeneous, but not uniform permanent magnet, by solving an eigenvalue problem. Finally, the fourth chapter deals with the numerical calculation of homogenized coefficients, which requires the resolution of a partial differential equation. We explore in this chapter a method using finite elements, as well as multi-grid methods
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Rehn, Jorge Armando. "Magnets with disorder and interactions:." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-220572.
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A very important step in the art of cooking up models for the study of natural phenomena is the identification of the relevant ingredients. Taking into account too many details will lead to an overly complicated model, not at all useful to work with, but neglecting some crucial elements will lead to an equally useless model. So it is often the case that the actual experimental situation presents unavoidable sources of local randomness, whilst the analysed phenomenon does not really rely on presence/absence of such imperfections. For some other set of phenomena, however, disorder can play a crucial role, and must be carefully taken into account. Such is for example the case in certain phases of matter, the spin-glass phase, or the many-body localised phase. In this thesis we explore disorder in both of these situations and also as a theoretical means of testing the regime of liquidity in certain two-dimensional highly frustrated magnetic models. The focus here is placed on classical Heisenberg models defined on lattices consisting of clusters all sites of which interact mutually pairwise. This natural way to introduce frustration has been known in the literature to lead to so-called Coulomb spin-liquids, the single class of classical spin-liquids acknowledged to exist so far in Heisenberg models. Here we show that in fact two different classes of classical spin-liquids can be obtained from similarly defined frustrated models. In one of these, algebraic correlations exist at $T=0$, similar to the Coulomb phase, but the system exhibits a rather different low$-T$ effective action from the Coulomb phase. In the other class, the spin-liquid has spin correlations that decay exponentially with distance, with a correlation length smaller than a lattice spacing even at $T=0$. One special effect of disorder in these models, considered in the form of dilution by non-magnetic impurities, is to nucleate local degrees of freedom, so-called orphans, which express the concomitant spin-liquid phase through their non-trivial fractionalisation. When the associated spin-liquid exhibit algebraic correlations, it is also possible to find new effective spin-glass models as an effective $T=0$ description for interactions between the orphans, leading to so-called `random Coulomb magnets'. One part of this thesis is devoted to the first study of these new models. This investigation consists mainly of Monte Carlo simulations and numerical solution of the relevant large$-n$ equations ($n$ being the number of spin components). A clear spin-glass transition for infinitely large coupling strength is determined for the case of spins with an infinite number of components. The results presented on the situation for a finite number of spin components are more of an exploratory character, and large-scale simulations with further optimization schemes to ensure equilibration are still required to locate the transition. The final investigation treated in this thesis deals with the dynamics in a quantum model with disorder displaying the many-body localized phase, where in addition a periodic drive is applied. For a certain range of driving frequencies and amplitudes, it was found recently that the many-body localized phase is robust. These pioneering studies restricted themselves to an analysis of the stability of such a phase in the long time limit, while very little was known about the dynamics towards the asymptotic fate. Our study focuses on this aspect, and analyses the different dynamical behaviors as one varies the driving parameters, so that the many-body localized phase survives or is destroyed by the driving. We discover that on the border between these two asymptotic fates, a new dynamical behavior emerges, where the system heats up at a very slow, logarithmic in time, rateDie Bestimmung der wichtigsten Bestandteile stellt einen sehr wichtigen Schritt in der Kunst des Erstellens von Modellen dar. Die Annahme von zu vielen Details ergibt ein sehr kompliziertes, zu nichts zu gebrauchendes Modell, doch die Vernachlässigung von bedeutenden Zusammenhängen führt ebenfalls zu einem unbrauchbaren Ergebnis. Es ist so z.B. häufig der Fall, dass ein Experiment unter dem Einfluss von unvermeindlichen lokalen Zufälligkeiten steht, die allerdings kaum einen Einfluss auf ein beobachtetes Phänomen haben. Für gewisse Phänomene spielt Unordnung jedoch eine wesentliche Rolle und sie muss sehr genau in Betracht gezogen werden. Das ist für bestimmte Phasen, wie beispielsweise Spinglas oder die Vielteilchen-Lokalisation, der Fall. In dieser Dissertation untersuchen wir ungeordnete Systeme, die solche Phasen aufweisen. Außerdem verwenden wir Unordnung als ein theoretisches Werkzeug für die Analyse von bestimmten `Spinflüssigkeiten' in zweidimensionalen Spinmodellen. Der Fokus liegt hierbei auf klassischen Heisenberg Modellen definiert auf Gittern, die aus einer Anordnung von Clustern bestehen, sodass jede einzelne paarweise Heisenberg-Wechselwirkung innerhalb eines Clusters stattfindet. Dadurch weist das System geometrische Frustration auf und in mehreren Fällen tritt eine sogennante Coulomb Spinflüssigkeit ---die bislang einzig bekannte Klasse von klassischen Spinflüssigkeit in Heisenberg Modellen--- auf. Wir zeigen, dass mindestens zwei weitere Arten von klassischen Spinflüssigkeiten in solchen Modellen zu finden sind. Für die eine Klasse sind Spinkorrelationen zu erwarten, die algebraisch mit der Entfernung bei $T=0$ abnehmen, ähnlich wie für eine Coulomb Phase. Diese neu entdeckte Spinflüssigkeit lässt sich jedoch von der Coulomb Phase durch eine neue effektive Tieftemperatur-Theorie unterscheiden. Für die andere Klasse von Spinflüssigkeiten sind die Spinkorrelationen kurzreichweitig, und selbst bei $T=0$ nehmen sie exponentiell ab, mit einer Korrelationslänge, die kleiner als ein Gitterabstand ist. Unordnung, in der Form von nicht-magnetischen Störstellen, kann lokale Freiheitsgrade entstehen lassen (diese werden in der Literatur auch als `Orphans', Waisen, bezeichnet). Die Orphans verweisen durch ihre `Fraktionierung' eindeutig auf die nicht trivialen Korrelationen der spinflüssigen Phase. Falls die Spinflüssigkeit algebraische Korrelationen aufweist, findet man auch langreichweitige Wechselwirkungen zwischen den Orphans bei $T=0$. Dies führt zu neuen Spinglasmodellen, sogenannten `Random Coulomb Magnets'. Ein Teil dieser Dissertation ist der Untersuchung solcher Modelle gewidmet. Diese Untersuchung besteht hauptsächlich aus Monte Carlo Simulationen und numerischer Lösung der relevanten Large-$n$ Gleichungen (wobei $n$ hier auf die Anzahl an Spinkomponenten hinweist). In dem Fall von Spins mit unendlich vielen Spinkomponenten können wir einen eindeutigen Spinglas Phasenübergang für eine unendlich große Kopplungsstärke bestimmen. Die entsprechenden Ergebnisse für den Fall von Spins mit einer endlichen Anzahl an Spinkomponenten sind von einem exploratorischen Charakter. Zusätzliche Simulationen, die möglicherweise weitere Optimierungsschema verwenden um Äquilibrium zu gewährleisten, sind noch von nöten um eine eindeutige Aussage über den Übergang in solchen Fällen zu treffen. Der letzte Teil dieser Dissertation widmet sich der Untersuchung der Dynamik eines ungeordneten Quantenmodells. Das ausgewählte Modell weist die sogennante Vielteilchen-lokalisierte Phase auf, und wir untersuchen insbesondere den Effekt eines periodischen Antriebs auf die Dynamik des Systems. Für eine bestimmte Auswahl der Antriebs-frequenz und -amplitude, wurde es bereits vor kurzem bewiesen, dass die Vielteilchen-lokalisierte Phase diese Störung übersteht. Unsere Studie ist darauf ausgelegt, wie sich die Dynamik des Systems durch Variation der Antriebsparameter ändert, so dass die Vielteilchen-lokalisierte Phase für lange Zeit entweder den Antrieb übersteht oder von ihm zerstört wird. Wir konnten dadurch entdecken, dass an der Grenze zwischen diesen beiden Fällen ein neues dynamisches Verhalten entsteht, bei der das System eine sehr langsame, logarithmisch mit der Zeit, Erwärmung aufweist
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Yoo, Jae. "Polynuclear manganese single-molecule magnets /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9988317.
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Andreescu, Radu. "Exchange coupled thin film magnets /." Search for this dissertation online, 2004. http://wwwlib.umi.com/cr/ksu/main.
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Shinohara, Hajime. "Doping studies of frustrated magnets." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/276013.
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Doping nonmagnetic materials is known as an effective way of investigating the properties of frustrated magnets. LiCuSbO4 is one of the simplest quasi-one dimensional spin-1/2 magnets which can be modelled with ferromagnetic(FM) nearest neighbour and antiferromagnetic (AFM) next nearest neighbour interactions. Here, doping with both non-magnetic ions, Zn, Mg, and magnetic ions, Co, is investigated. LiCu1-xMxSbO4 (M=Mg, Zn, Co 0≦x≦0.1) samples were synthesized by a ceramics process. At higher doping levels (x≧0.04), paramagnetic Curie features are observed below 4 K, however the broad peak characteristic of short range ordering at 6 K is retained. Isothermal magnetization indicates that the critical field found at 12 T in LiCuSbO4 was shifted by Zn and Mg doping. While the field is increased as the amount of Mg doping, it was increased as Zn doping in the range of 0≦x≦0.02 but decreased by x≧0.04. The trend in critical field is observed to follow that of the c lattice parameter for both Zn and Mg doping. On doping with Co2+ (S = 3/2), a low temperature Curie feature was observed from x=0.02. The value of the critical field increased on doping from (x=0) 12 T for 13.5 T (x=0.10). As for non-magnetic doping the trend in Hc has the same behaviour as the lattice parameter. The effect of doping on the pyrochlore spin ice A2B2O7 is also explored. The effect of oxygen vacancies induced by the aliovalent substitution on the B site on the crystal electric field was explored in the ceramic solid solutions. The effect of aliovalent doping on the pyrochlore A2Sn2(1-x)Sc2xO7-x (A=Ho and Dy 0≦x≦0.10) Tb2B2(1-x)Sc2xO7-x (B=Sn and Ti 0≦x≦0.05) were studied. While no dramatic changes of the saturation value of isothermal magnetization and heat capacities was observed in Dy2Sn2O7 by Sc doping in the range of 0≦x≦0.1, the saturation value of isothermal magnetization and magnetic entropy in Ho2Sn2O7 was clearly increased by Sc doping more than x=0.05, This difference could be from the difference of Kramer’s and non-Kramer’s spins between Dy and Ho, as while Dy is a Kramer’s ion and its ground state is protected, Ho is a non-Kramer’s ion and its ground state could be split. While Tb2Sn2O7 is known as quantum spin ice, Tb2Ti2O7 is known as spin liquid. A peak at 6 K of heat capacity, which is assigned as being due to a crystal electric field excitation to an excited doublet in Tb2Sn2O7 and Tb2Ti2O7 was observed in the Tb2Sn2(1-x)Sc2xO7-x sample. However in Tb2Ti2(1-x)Sc2xO7-x it was not observed. This indicates that the increased strain in the ceramic solid solution has a larger impact on the crystal electric field.
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RICCI, ALESSANDRO MARIA. "Superconducting magnets for future accelerators." Doctoral thesis, Università degli studi di Genova, 2020. http://hdl.handle.net/11567/1002038.
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The Large Hadron Collider (LHC) at CERN, which is now in operation for ten years, is not only the largest and more powerful particle accelerator in the world, but also constitutes one of the greatest applications of the superconducting magnet technology. Nevertheless, the need to increase both the luminosity in the next future and the energy in more far future is demanding for the developments of new and more challenging superconducting magnets generating higher magnetic fields. Presently all laboratories worldwide involved in the superconducting magnet technology for accelerators are performing R&D activities aimed to the development of a high field superconducting magnet (16 T) for the Future Circular Collider, an accelerator for 50-TeV energy protons (7 times higher than the energy of the LHC beams). The needed technology demands for the use of superconducting material (Niobium Tin) well-known but of difficult application requiring a considerable development before it can be used for 16-T magnet. It is also under study the possible use of cables based on high critical temperature superconductors (HTS), which are even more difficult and have never been used in accelerators.
The design of the superconducting magnets for accelerators is closely related to the physics of the accelerator. In particular, the optics of the beams is determined by the quality of the magnetic field controlled by dipoles, quadrupoles and higher-order correctors. To a greater extent than existing magnets, the optimization of a magnetic design for the dipoles of the Future Circular Collider, for energies of 100 TeV in the center of mass, has many critical aspects partly related to the intrinsic limitations of superconducting cables (critical fields and currents) and partly to the need to develop stable geometric layouts with respect to geometric variations (mechanical deformation or manufacturing tolerances).
This thesis is focused on the optimization of the field quality for the magnets in the twin-coil configuration (for FCC as for LHC the two openings of the dipoles that curve the proton beams circulating in the opposite direction are assembled in a single cold mass). For this class of magnets, the magnetic cross-talk between the apertures presents considerable complications considering that in a dipole the components of higher-order multipoles must be at the most of the order of 10^-4 with respect to the main dipole field. We have developed analytical methodologies, complemented with numerical analyzes, to minimize magnetic cross-talk through suitable asymmetrical configurations. We have applied these methodologies in the various studies carried out for the development of magnets for the Future Circular Collider contributing to finalize a design, which has been presented as the baseline of an European project funded within H2020 framework, named EuroCirCol. We have also applied the developed methods for studying possible improvements to the present design of the recombination dipoles (called D2) for the high luminosity upgrade of LHC. These are NbTi magnets with a strong cross-talk between the two apertures and are under construction at ASG Superconductors in Genova with a design developed at INFN Genova. At the same time, we have developed the 3D electromagnetic models of both magnet classes. In particular, we have been responsible for the 3D electromagnetic simulations of the EuroCirCol magnet. Finally, we have helped to develop a preliminary design of the FCC recombination dipoles (called DARD), which have required a completely different approach with respect to the D2 magnets for LHC.
The thesis is structured in two main sections with five chapters. The first section (including three chapters) reports the theoretical background and the developed methods. The second section (two further chapters) reports the design activities of the magnets for the high luminosity upgrade of LHC and for FCC.
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Matsumoto, Kenshi. "Crystal Structural Control of Nanomaterials toward High-Performance Permanent Magnets." Kyoto University, 2019. http://hdl.handle.net/2433/245309.
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