Tesis sobre el tema "Magnetocaloric materials, hard magnetic materials"
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Quetz, Abdiel. "EXPLORATION OF NEW MAGNETOCALORIC AND MULTIFUNCTIONAL MAGNETIC MATERIALS". OpenSIUC, 2017. https://opensiuc.lib.siu.edu/dissertations/1378.
Texto completoBayer, Daniel Nicholas. "The Magnetocaloric Effect & Performance of Magnetocaloric Materials in a 1D Active Magnetic Regenerator Simulation". Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1578587695272946.
Texto completoAryal, Anil. "EXPLORATION OF NOVEL MAGNETOCALORIC MATERIALS FOR APPLICATIONS IN MAGNETIC COOLING TECHNOLOGY". OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1813.
Texto completoNguyen, Van Tang. "Nanostructured soft-hard magnetic materials with controlled architecture". Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1007.
Texto completoAmong currently investigated rare-earth-free magnets, ferromagnetic τ-MnAl is a highly potential candidate as having promising intrinsic magnetic properties. In my thesis, Mn(Fe)AlC was synthesized by mechanical alloying method. Effects of carbon on microstructure and magnetic properties were systematically investigated. It was found that high purity of τ-MnAl(C) could be obtained at 2 at.% C doping, showing clearly stabilizing effect of carbon. Mn54.2Al43.8C2 has the best magnetic properties: magnetization at 2T M2T = 414 kAm-1, remanent magnetization Mr = 237 kAm-1, coercivity HC = 229 kAm-1, and |BH|max = 11.2 kJm-3. HC increased inversely with the crystallite size of τ phase and proportionally with C content. Moreover, first principle calculation showed both stabilizing effect and preferable interstitial positions of carbon in tetragonal τ-MnAl. Mn51-xFexAl47C2 (x= 0.25, 0.5, 1, 2, 4, 6) alloys were also synthesized by mechanical alloying method, showing high purity of τ phase up to 2 at.% Fe doping. Adding of Fe on MnAl(C) reduced both magnetization and TC but likely increased slightly HC. 57Fe Mössbauer spectrometry at 300K was used to probe local enviroment in ε-, τ-, β-, and γ2-MnFeAl(C). In which, γ2-, ε-, and β-MnFeAl(C) exhibited a quadrupolar structure while τ -Mn50.5Fe0.5Al47C2 spectrum showed a rather complex magnetic hyperfine splitting. The interaction between Fe and Mn examined by in-field Mössbauer measurement at 10 K and 8 T showed a non-collinear magnetic structure between Fe and Mn with different canting angles at different sites. Hyperfine field of MnFeAl alloy calculated by Win2k supported both magetic properties and Mossbauer results
Strandqvist, Nanny. "Magnetic Properites in Alloy Systems". Thesis, Luleå tekniska universitet, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62614.
Texto completoHudl, Matthias. "Magnetic materials with tunable thermal, electrical, and dynamic properties : An experimental study of magnetocaloric, multiferroic, and spin-glass materials". Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-168986.
Texto completoChaturvedi, Anurag. "Novel Magnetic Materials for Sensing and Cooling Applications". Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3040.
Texto completoLuo, Haihua. "Synthesis and characterization of rare-earth-iron based hard magnetic materials /". free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9924902.
Texto completoMarashi, Seyed Pirooz Hoveida. "Transmission electron microscopy study of nanostructured Nd-Fe-B hard magnetic materials". Thesis, University of Sheffield, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366102.
Texto completoTsui, Hei Man. "Synthesis and Characterization of Magnetic Cabides and Oxides Nanomaterials". VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5366.
Texto completoGhirlanda, Simone L. "Prototype and Testing of a MEMS Microcooler Based on Magnetocaloric Effect". Scholar Commons, 2006. http://scholarcommons.usf.edu/etd/3890.
Texto completoMéndez, de la Luz Diego A. 1979. "The role of heat assisted magnetic recording in future hard disk drive applications". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28872.
Texto completoIncludes bibliographical references.
(cont.) portable consumer electronics, such as PDAs, cell phones, music players, digital cameras, etc. make a relatively modest but fast growing market for ultrahigh areal density HAMR-based HDDs. HAMR-based HDD for portable applications could very well be a disruptive technology in the magnetic recording industry. Companies that intend to profit from this technology need to invest on its development and must try to be first-to-volume production to benefit from economies of scale and to build the necessary expertise that could give them leadership roles in future magnetic recording.
The magnetic recording industry keeps up with the demand of high capacity hard disk drives by improving the areal recording density of these devices. The use of conventional longitudinally magnetized media will be truncated by the challenges it faces nowadays, which are related to the instability of the stored information, produced by the aggressive decrease in the volume of the grains in the media. To overcome this problem, the use of large magnetic anisotropy energy density alloys is necessary, but the write fields that are required by such alloys can be prohibitively large, rendering these media effectively unwritable. Fortunately, the magnetocrystalline anisotropy energy density decreases with increasing temperature and so does the required write field. Heat assisted magnetic recording allows the use of such magnetically hard alloys by using both a magnetic and a thermal field during the writing process. Research in HAMR is centered in three major fields: the heat delivery system, the magnetic recording media and the heat dissipation technology. Based on an analysis of several US patents related to HAMR, one can see the real value of such patents is in negotiating and cross-licensing between companies to guarantee the right to participate in the manufacture of HDDs. Trade secrets and know-how are valuable assets for corporations. However, information exchange exists due to the great mobility of highly trained personnel between competing companies. Because the basic application of HAMR is in supplying the computer industry with affordable storage devices, there is a well established market that makes the research efforts in HAMR advisable for individuals, universities and companies. Besides that traditional market,
by Diego A. Méndez del la Luz.
M.Eng.
Pandey, Sudip. "EXPLORING THE STRUCTURAL, ELECTRONIC, AND MAGNETORESPONSIVE PROPERTIES OF NOVEL MAGNETIC MATERIALS IN BULK, RIBBONS, AND THIN FILMS". OpenSIUC, 2019. https://opensiuc.lib.siu.edu/dissertations/1682.
Texto completoPathak, Arjun Kumar. "EXPLORATION OF NEW MULTIFUNCTIONAL MAGNETIC MATERIALS BASED ON A VARIETY OF HEUSLER ALLOYS AND RARE-EARTH COMPOUNDS". OpenSIUC, 2011. https://opensiuc.lib.siu.edu/dissertations/353.
Texto completoDas, Ranjit Chandra. "The Effect of Stoichiometric Variation on the Magnetocaloric Properties of Selected Mn-Fe-Ni-Si-Al Intermetallic Compounds". Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1626959102771612.
Texto completoPickford, Rachael Anne. "A study of magnetic properties of hard and soft magnetic materials by Lorentz transmission electron microscopy and magnetic x-ray circular dichroism". Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367489.
Texto completoGass, James. "Functional Magnetic Nanoparticles". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4047.
Texto completoAkintunde, Babajide O. "A study on the effect of Fe-Ni variation on the magnetocaloric properties of Mn0.5Fe0.5+xNi1-xSi0.94Al0.06 and Mn0.5Fe0.5-xNi1+xSi0.94Al0.06 systems". Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami16267284137581.
Texto completoBavendiek, Gregor Johannes [Verfasser]. "A contribution to the electromagnetic Finite Element Analysis of soft and hard magnetic materials in electrical machines / Gregor Johannes Bavendiek". Düren : Shaker, 2020. http://d-nb.info/122060996X/34.
Texto completoSözen, Halil Ibrahim [Verfasser], Gunther [Gutachter] Eggeler y Jörg [Gutachter] Neugebauer. "Ab initio phase stabilities of Ce-based hard magnetic materials / Halil Ibrahim Sözen ; Gutachter: Gunther Eggeler, Jörg Neugebauer ; Fakultät für Maschinenbau". Bochum : Ruhr-Universität Bochum, 2019. http://d-nb.info/1199614475/34.
Texto completoTedesco, Julio Cesar Guimarães 1973. "Estudo magnético e calorimétrico sobre a série TbxPr1-xAl2". [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277272.
Texto completoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Neste trabalho propomos o estudo de algumas propriedades magnéticas e do efeito magnetocalórico (EMC) de compostos da família TbxPr1-xAl2, onde x = 0,1; 0,2; 0,25; 0,3; 0,4; 0,5 e 0,75. É fato conhecido que dois elementos terras-raras se acoplam antiferromagneticamente quando inseridos em uma rede cristalina do tipo (R,R¿)Al2 se um deles é um elemento terra-rara leve o outro pesado. Desta forma, era esperado que as amostras desta série apresentassem um ordenamento ferrimagnético, o que foi confirmado pelos nossos dados. Comparamos nossos resultados com sistemas semelhantes e com eles fomos capazes de entender a origem de algumas características e aspectos físicos dos materiais, incluindo o EMC. Alguns compostos estudados aqui apresentaram o efeito magnetocalórico inverso, que acontece devido à competição entre as duas subredes magnéticas acopladas antiferromagneticamente. Observamos também os comportamentos da temperatura de transição magnética e dos parâmetros de rede em função da concentração de Tb, e verificamos o deslocamento dos picos do EMC associados à temperatura de transição (TC). Algumas propriedades importantes na aplicação destes materiais em refrigeração magnética foram levantadas e comparadas com a literatura. Verificamos que dois membros da série apresentaram o efeito de Exchange Bias (EB) e, em analogia com sistemas bicamadas FM-AFM em filmes finos, fomos capazes de entender e explicar este efeito. Acreditamos que o efeito de Exchange Bias está associado à forte anisotropia apresentada pelos compostos Tb0.3Pr0.7Al2 e Tb0.25Pr0.75Al2 que ocorre em temperaturas extremamente baixas e à magnetização dos elétrons polarizados de condução. Identificamos também as temperaturas de compensação (propriedades características deste tipo de sistema) nestes compostos
Abstract: In this work we studied some magnetic properties and the magnetocaloric effect (MCE) of the series of compounds TbxPr1-xAl2, where x = 0.1, 0.2, 0.25, 0.3, 0.4, 0.5 and 0.75. It is known from the literature that the moments of a light and a heavy rare earth are antiferromagnetically coupled when they are inserted in a crystal lattice and this was confirmed by our analysis of the experimental data. We compared our results with similar systems and we were able to understand the origin of some features and physical aspects of those materials, including the magnetocaloric effect (MCE). Some compounds show the inverse MCE, associated to the competition between the two magnetic sublattices antiferromagnetically coupled. We also observed the behavior of the magnetic transition temperature (TC) and lattice parameters as a function of the concentration ('x¿), with a corresponding MCE peak shift. Some important properties regarding the application of these materials in magnetic refrigeration are discussed. Two members of the family of compounds show a shifted hysteresis curve which was assigned to the Exchange Bias (EB) effect in analogy with FM-AFM bilayers systems in thin films. We believe that the EB effect is associated with strong unidirectional anisotropy of the magnetic sublattices appeared in Tb0.3Pr0.7Al2 and Tb0.25Pr0.75Al2, which occurs at low temperatures, and with the magnetization of the polarized conduction electrons. We also identified the compensation temperature (characteristic properties of this type of system) in these compounds
Doutorado
Física
Doutor em Ciências
Venkataramana, Vikash. "Neutrons to probe nanoscale magnetism in perpendicular magnetic recording media". Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3187.
Texto completoValkass, Robert Alexander James. "Exploration of the sub-nanosecond magnetisation dynamics of partially built hard disk drive write-head transducers and other topical magnetic and spintronic materials and devices". Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/31175.
Texto completoAhmim, Smail. "Conversion de la chaleur fatale de bas niveau en énergie électrique par effet magnétocalorique". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST015.
Texto completoThe main objective of my thesis is the design and development of a device suitable to recover, and scavenge, low grade heat to produce electrical energy and thus supply small autonomous systems (μW to mW). The developed generator converts energy in three steps. First of all, thermal energy is converted into magnetic energy through a thermodynamic cycle operated by a magnetocaloric material. This first conversion is closely linked to the second, conversion of magnetic energy into mechanical energy, because the displacement of the magnetocaloric material also controls the applied field and the heat exchanges with the reservoirs. It is the interweaving of these two cycles, thermodynamic and dynamic, which allows the system to self-oscillate. The mechanical energy of the pseudo-oscillating system is converted into electrical energy via piezoelectric elements. My experimental, theoretical and numerical works aimed to maximize the electrical energy recovered while ensuring the self-oscillation of the structure. All devices developed are able to self-oscillate for temperature difference of 35 °C while producing electrical energy. Our most efficient prototype has an energy of 10.6 μJ per cycle for a frequency of 0.41 Hz, i.e. a power of 4.2 μW (240 μW/cm3). This work, especially, focuses on the cycles associated with energy conversion
Chennabasappa, Madhu. "Etude du vieillissement de matériaux magnétocaloriques". Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14970/document.
Texto completoMagnetic refrigeration has gained lot of importance and attention as they are highlighted to be environmental friendly, energy efficient. Presently, though at research stage, the magnetic refrigerators are pushed towards realization in domestic application with extensive work on materials and with few working models. One critical issue, the potential resistance to corrosion in case of different class of magnetocaloric materials (Gd6Co1.67Si3, Ni2Mn0.75Cu0.25Ga and Pr0.66Sr0.34MnO3) against the heat transport fluid is addressed. To better understand and improve the observed magnetocaloric properties in Heulser alloys Ni2Mn0.75Cu0.25Ga and to elaborate the same with the magneto-structural relation, studies on (i) cation distribution with in crystal structure and/or (ii) microstructural dependence are presented. Nuclear and magnetic phase diagram based on detailed neutron diffraction and magnetism studies for magnetocaloric perovskite oxide Pr1-xSrxMnO3 (0.25≤x≤0.45) is also presented
Legait, Ulrich. "Caractérisation et modélisation magnétothermique appliquée à la réfrigération magnétique". Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00612428.
Texto completoSardinha, Farley Correia. "O efeito magnetocalórico nas ligas Heusler Ni54[Mn(1-x)Fex]19Ga27". Universidade Federal do Espírito Santo, 2008. http://repositorio.ufes.br/handle/10/6285.
Texto completoConselho Nacional de Desenvolvimento Científico e Tecnológico
In this work, magnetic entropy change of nonstoichiometric Ni54[Mn(1-x)Fex]19Ga27 Heusler alloys was experimentally verified by partial substitution (up to 50%) of the Mn atoms by magnetic Fe atoms. Such study was mainly concentrated in the magneto-structural transformation region, at low temperatures. The analysis of X-ray diffraction patterns indicate that the partial substitution of Mn atoms by Fe atoms causes predominance of the L21 -phase, however accompanied by spurious phases. The magnetization measurements as a function of the temperature in the low magnetic field reveals that, in all concentration range (0 x 0.5), the system presents a magnetic transition (Ferromagnetic Paramagnetic) at a temperature, TC, near the room temperature, when the material lay in the austenitic phase. Moreover, as many others Heusler alloys, the material undergoes a martensitic structural transition at low temperatures, TM. As the Fe concentration increases, the Curie temperature, TC, undergoes a little variation, increasing around 5%, while TM decreases slowly and monotonically. The magnetic entropy change, for a field of 5T, presents a maximum SM = - 9,3 J/kg.K, for x = 0.1, at a temperature of 250K, and than decreases for x 0.3, changing linearly with the maximum applied field.
Neste trabalho, verificou-se experimentalmente a variação da entropia magnética nas ligas Heusler não-estequiométricas Ni54[Mn(1-x)Fex]19Ga27, substituindo-se parcialmente (até 50%) os átomos de Mn por átomos de Fe. Tal estudo focalizou-se principalmente na região de transformação magneto-estrutural a baixas temperaturas. A análise dos difratogramas de raios-X indica que a substituição parcial de Mn por Fe nessa faixa de concentração, ocasiona uma predominância da fase- L21, porém acompanhada de outras fases espúrias. As medidas de magnetização em função da temperatura realizadas a campos baixos revelam que, em toda a faixa de concentração estudada (0 x 0,5), o sistema apresenta uma transição magnética (Ferromagnético Paramagnético) ao atingir a temperatura de Curie, TC, um pouco acima da temperatura ambiente, quando o material se encontra na fase austenítica. E, assim como muitas outras ligas Heusler, o material sofre uma transição estrutural ao ser resfriado a temperaturas inferiores à temperatura de transição martensítica, TM. À medida que se aumenta a concentração de Fe, a temperatura de Curie, TC, sofre uma pequena variação, aumentando em torno de 5%, enquanto que TM diminui lenta e monotonicamente. A variação da entropia, para um campo de 5T, apresenta um máximo SM = - 9,3 J/kg.K para x = 0,1, a uma temperatura T = 250K e, então, diminui para x 0,3, variando linearmente com o campo aplicado.
Rouxinol, Francisco Paulo Marques 1977. "Propriedades magnéticas de filmes de ligas GD-Cr". [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278407.
Texto completoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Técnicas de condensação de vapor são úteis na preparação de ligas magnéticas cujos componentes têm pouca, o mesmo nenhuma, solubilidade em condições de equilíbrio Neste trabalho, uma dessas técnicas ¿ sputtering ¿ foi empregada para fabricar ligas metaestáveis de GdXCr1-X, cujas propriedades magnéticas foram investigadas em função da concentração de Gd, x. Difratometria de raios-X de baixo ângulo (GAXRD) e espectroscopia de retroespalhamento Rutherford foram utilizados para determinar a estrutura do filme e sua composição elementar, respectivamente. As análises de GAXRD mostraram que a estrutura da fase de Gd, é hcp quando x ³ 0,88; e amorfa quando 0,16 £ 0,76. Uma estrutura bcc , para a fase de Cr, foi observada nos difratogramas quando x < 0,16, e amorfa quando x ³ 0,16 Para investigar as propriedades magnéticas utilizamos um magnetometro SQUID e m PPMS. O primeiro foi utilizado para as medidas de momento magnético em função do campo estático e temperatura. O PPMS foi tilizado nas investigações de susceptibilidade-AC em função da freqüência de oscilação do campo, temperatura e campo estático. A complexa natureza magnética dos filmes de Gd-Cr foi observada através das isotermas MxH, que não apresentaram saturação em baixas temperaturas, nem comportamento linear em altas temperaturas. Pela análise dos dados magnéticos, observamos que as amostras admitem um comportamento ferromagnético para x ³ 0,5 e paramagnético para as outras concentrações de Gd. A temperatura de Curie (TC) apresenta um aumento monotônico de 170 para 290 K quando x aumenta de 0,5 para 1,0. A temperatura de Curie-Weiss (q C) mostra um aumento monotônico com x. A partir das isotermas MxH a 2 K, o momento de saturação foi calculado, sendo independente de x e aproximadamente constante com um valor médio de 7,3 µB. Medidas de susceptibilidade em campos estáticos e dinâmicos revelaram a existência de comportamentos de vidros magnéticos em todas as amostras abaixo da temperat ra de freezing (Tf). Observamos, nas ligas com altas concentrações de Gd, a presença de comportamentos ferromagnéticos e cluster-glass em baixas temperaturas. Concluímos que a interação de troca entre os átomos de Gd dentro dos clusters de Gd não é do tipo RKKY, e sim do tipo supertroca. O efeito magnetocalórico (MCE) foi investigado através da variação de entropia magnética ( D SM) em função da temperatura, para a remoção de um campo de 50 kOe Curva de D SMxT para as amostras com x < 0,2 apresentaram um formato típico de superferromagneto, consistente com a existência de clusters Gd nos filmes. Nas outras amostras em que o EMC foi analisado, a presença de clusters é observada pelo comportamento dessas curvas a baixa temperatura; a altas temperaturas o comportamento de D SM com T indica fortemente a presença de mais fases magnéticas no filme. O diagrama de fase baseado em TC e Tf, e sua dependência com x é apresentado
Abstract: Vapor condensation techniques are very useful for preparation of alloys whose components have no mutual solubility under equilibrium conditions In this work, one of these techniques ¿ sputtering ¿ has been used to fabricate metastable GdXCr1-X alloys whose magnetic properties were investigated as a function of the Gd concentration, x. Grazing incidence angle X-ray diffraction (GAXRD) and Rutherford backscattering spectroscopy were employed to characterize the film structure and elemental composition, respectively. The GAXRD measurements revealed, for the Gd fraction, a hcp structure for x ³ 0,88; for 0,16 £ x £ 0,76 the Gd fraction was amorphous. The existence of a bcc structure for x < 0,16 was observed in the diffractograms for the Cr phase, which was amorphous for x ³ 0,16. To investigate the magnetic properties, a SQUID magnetometer and a PPMS were used. The former was employed for magnetic moment measurements as a function of applied static field and temperature. The PPMS was used for ac-susceptibility determinations as a function of the frequency of the ac driving field, temperature, and applied static field. The complex magnetic nature of the Gd-Cr films was revealed from the MxH isotherms which did not show saturation even at the lowest temperatures, and did not exhibit a linear behavior at higher temperatures. Processing of the magnetic data has shown that the films exhibit a ferromagnetic behavior for x ³ 0,5 and paramagnetic one for all other Gd concentrations. The Curie temperature (TC) increased monotonically from 170 to 290 K as x increased from 0,5 to 1,0. A monotonical increase in the Curie-Weiss temperature ( q C ) with x was also observed for all films. From the extrapolated MxH isotherm at 2 K (saturation magnetization), the saturation moments were calculated and found to be nearly constant at about 7.3 µB. Both static and dynamic susceptibility measurements revealed the existence of a magnetic glassy behavior in all alloys, occurring below a freezing temperature Tf . For the higher concentration alloys, the ferromagnetic and the cluster glass state were observed at low temperatures. It was thus concluded that the exchange interactions within Gd atoms in the clusters were not of the RKKY but of the superexchange type. The magnetocaloric effect (MCE) was investigated from the magnetic entropy change ( DSM) as a function of temperature, for the removal of a 50 kOe field. Samples with x < 0,2 exhibited DSMxT curves whose shapes are typical of a superferromagnet, consistently with the existence of Gd clusters in the films. For all the other alloys whose MCE was investigated, the presence of clusters is manifested from the behavior of these curves at low temperatures; at higher temperatures, the evolution of DSM with T strongly indicated the presence of more than one magnetic phase in the alloys A magnetic phase diagram based on the Tf and Tc transition temperatures and their dependence on x is presented in this thesis
Doutorado
Física da Matéria Condensada
Doutor em Ciências
Kevorkian, Brindusa Maria. "Contribution à la modélisation du retournement d'aimantation : application à des systèmes magnétiques nanostructurés ou de dimensions réduites". Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10096.
Texto completoKerschl, Peter. "Magnetisierungsmessungen in hohen magnetischen Impulsfeldern". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1155114785406-30409.
Texto completoIn this work, the occurrence and the mechanism of field induced transitions and the related critical fields were investigated. The way of measuring the magnetisation was designed for the existing pulsed field device of the IFW Dresden. The magnetisation was measured in fields up to 48 T. For the first time, the anisotropy coefficient of Sm2Fe17N3 was obtained in the combined measurement of the exchange field via inelastic neutron scattering and the measurement of the anisotropy constant K1 for the same material. For the leading anisotropy coefficient, a value of A20<r²> = -28 meV was found using K1 of about 13 MJ/m³. It was shown that the observed high field transition in SmCo2.5Cu2.5 and SmCo2Cu3 is connected with the microstructure. The laminar microstructure consisting of phases with different Sm-content is a necessary precondition for the occurrence of the transition. The coercivity increases with the Cu-content and reaches high values at low temperature. The coercivity and the transition field show big magnetic viscosity. In DyFe6Al6, the disappearance of the spontaneous magnetisation at low temperature is caused by a strong antiferromagnetic coupling. The magnetic transition at low temperature could be explained by a field induced magnetic moment on a disordered crystal site. For the hexagonal DyMn6Ge6, the temperature dependence of the transition field towards the canted antiferromagnetic structure was measured for the first time. Above 100 K, the applied field causes the transition from the helimagnetic to the fan structure. At low temperature, a spin flop transition occurs, which is supported by the magnetic anisotropy of the Dy-ion. The magnetisation of magnetocaloric materials exhibits a dependence of the field changing rate. This can be explained qualitatively by the measurement condition: The pulsed field measurement is adiabatic, whereas during static measurements, the condition is isothermal. Besides common magnetic compounds, highly correlated electron systems were also investigated. The magnetic transition at 43 T in CeNi2Ge2 can be explained by the suppression of the Kondo effect and the breaking up of the antiferromagnetic structure. Furthermore, magnetisation of high temperature superconductors was measured. The measurements in the pulsed field are a contribution to the determination of the phase diagram of melt textured YBa2Cu3O7-d. The irreversibility field Hirr was measured for bulk samples down to low temperature. Hirr(T) shows an unexpected linear increase down to low temperature. Because of the high field-changing rates and the big differences of magnetisation processes in magnetic materials, there is no uniform description of the magnetic viscosity for field changing rates in the magnitude from 0,001 up to 1000 T/s. By the measurement in the pulsed field, the magnitude of the magnetic viscosity of nanocrystalline barium ferrite was determined. Magnetisation measurement in pulsed fields is a very useful instrument to investigate field and time dependent properties of solids due to their high magnetic field and their high and varying field changing rate
Dupuis, Cédric. "Matériaux à effet magnétocalorique géant et systèmes de réfrigération magnétique". Phd thesis, Université de Grenoble, 2009. http://tel.archives-ouvertes.fr/tel-00566193.
Texto completoDavarpanah, Amin. "Tricritical magnetocaloric materials synthesis and their thermal properties characterization". Doctoral thesis, 2020. http://hdl.handle.net/10773/30479.
Texto completoEste trabalho apresenta uma abordagem inovadora para a avaliação de materiais promissores para aplicações magnetocalóricas. Inicialmente, a teoria do campo médio molecular (modelo Bean-Rodbell) é aplicada para simular vários sistemas magnéticos que descrevem transições de primeira e de segunda ordem. Os sistemas magnéticos de transição de segunda ordem são analisados para encontrar a composição com performance otimizada para uma mudança de campo magnético comparável aos valores práticos (até 2 Tesla). Além disso, a histerese intrínseca que ocorre em materiais de primeira ordem é estimada, sob certas alterações de campo magnético, e o seu impacto na capacidade de arrefecimento dos materiais é calculado. O candidato mais eficiente em termos de capacidade de refrigeração é detectado através da comparação entre materiais com vários comportamentos diferentes na transição. Um conjunto de amostras da família magnetocalórica La2/3(Ca1-xSrx)1/3MnO3 com transições variando de segunda e primeira ordem foi produzido e os dados foram ajustados com a ferramenta de simulação e parâmetros como valor de spin e o parâmetro de acoplamento magneto-volume. Sistemas magnéticos semelhantes às amostras experimentais foram simulados e a capacidade de arrefecimento do sistema simulado e amostras experimentais foram comparadas para verificar o modelo teórico. A dependência da temperatura da condutividade térmica dos sistemas La-Ca-Sr-Mn-O e Mn-Fe- P-Si foi medida e mostra alterações de até 50% dentro das faixas de temperatura de operação, além de um comportamento totalmente contrastante para as duas famílias de materiais magnetocalóricos. Também é mostrado que a dependência na temperatura da condutividade térmica é coordenada com a ordem da transição magnética. Sintetizando a família de amostras de La1-x(Ce, Pr, Nd)xFe11.6Si1.4 por meio de uma combinação de técnicas de fusão por indução e fundição por sucção, a faixa de substituição é expandida até x = 0.4. O impacto da substituição de La nas características magnetocalóricas, incluindo alteração da entropia magnética, mudança de temperatura adiabática, Tc e histerese, é investigada. Finalmente, a ordem de transição de fase é estudada usando métodos baseados na dependência de campo do efeito magnetocalórico (incluindo o modelo Bean-Rodbell).
Programa Doutoral em Ciência e Engenharia de Materiais
Christiaanse, Theodor Victor. "Characterization, experimentation and modeling of Mn-Fe-Si-P magnetocaloric materials". Thesis, 2018. https://dspace.library.uvic.ca//handle/1828/10376.
Texto completoGraduate
Chen, Chung-Yo y 陳重佑. "Study on Selective Laser Melting of NdFeB Hard Magnetic Materials". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/vh5pd5.
Texto completo國立交通大學
機械工程系所
106
This thesis will study on melting and forming of the isotropic NdFeB powder (MQP-S-11-9) by using selective laser melting system. Control the cooling rate by changing process parameters such as multi-beams, single-beam and laser parameters, and study the effects of different parameters on the hard magnetic phase and magnetic properties. By additive manufacturing technology, the limitations such as shape, internal hollow structure, and the same magnetism in one component, are overcome. The experiments are divided into single-beam and multi-beam systems. In the multi-beam experiment, the X-ray diffraction analysis measurement data of the single-layer structure can be used firstly to confirm that the CW mode laser source will cause too much α Fe content in the finished product and low magnetic energy product. During the experiment, we will control repetition rate, pulse duration, scanning speed and hatching distance. The results showed that scanning speed is the main factor on the magnetic properties. As the scanning speed increased, the maximum energy product also improved. In single-beam experiment, scanning speed can overcomes the limitation in multi-beam system, and furthermore increase cooling rate and improve maximum energy product. During the experiment, it was also found that if the thickness of the powder layer was reduced from 40 μm to 25 μm and the overlapping rate of melted track was increased, the magnetic properties could be efficiently improved.
Wagh, Aditya A. "Electric, Magnetic and Magnetocaloric Studies of Magnetoelectric GdMnO3 and Gd0.5Sr0.5MnO3 Single Crystals". Thesis, 2014. http://etd.iisc.ernet.in/2005/3512.
Texto completoWu, Dangxin. "First-principles study on hard/soft SmCo5/Co(Fe) nanocomposite magnetic materials". 2008. http://hdl.handle.net/10106/1042.
Texto completo(8800547), George Agbeworvi. "ENGINEERING MAGNETIC TRANSITIONS AND MAGNETOCALORIC EFFECT IN RARE-EARTH TRANSITION METAL ICOSAGENIDES". Thesis, 2020.
Buscar texto completoKim, Jihwan. "Magnetic exchange coupling in hard-soft ferromagnetic composite thin films of CoPt-Co : role of processing and structure /". Diss., 2001. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3010409.
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