Dissertations / Theses on the topic 'Magnetic propertie'
To see the other types of publications on this topic, follow the link: Magnetic propertie.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Magnetic propertie.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Ben, ghzaiel Tayssir. "Synthèse, caractérisation et étude des propriétés magnétiques et diélectriques de nanocomposites Polyaniline/hexaferrite pour l'absorption des micro-ondes." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLN003/document.
Full textAbstract:
Ces travaux de thèse consistent à élaborer des nanocomposites Polyaniline/hexaferrite pour l’absorption des micro-ondes. L’idée principale est la mise en œuvre de matériaux composites à base de polymères conducteurs intrinsèques telle la Polyaniline que nous avons dopée avec différents types d’acides (HCl, CSA, NSA et TSA…) et l’hexaferrite de baryum de type magnétoplombite (M) stœchiométrique ou substitué. Au niveau de l’hexaferrite de baryum, la substitution du Fe3+ s’est faite par les ions Al3+, Bi3+, Cr3+ et Mn3+.L’hexaferrite de baryum et les hexaferrites substitués par les différents ions cités ci-dessus ont été synthétisés par voie hydrothermale dynamique en faisant varier divers paramètres au cours de la synthèse (pH, température, temps, rapport [OH-]/[NO3-]…).L’élaboration des composites Polyaniline/hexaferrite (pur ou substitués) a été effectuée par polymérisation oxydative en utilisant plusieurs techniques de synthèse : la polymérisation chimique en solution (en tenant compte de la nature de l’acide utilisé) avec ou sans agitation (Aqueous-Based Polymerization with or without stirring) et la polymérisation oxydative par voie solide (Solid-Based Polymerization). L’optimisation de ces différentes techniques de synthèse après caractérisations physicochimiques (DRX, FTIR, ATG, MEB, EDX), diélectriques (ε’, ε’’, σdc) et magnétiques (Mr, Ms, Hc, Tc, µ’, µ’’) des échantillons, a montré que la polymérisation par voie solide se trouve la méthode la plus facile, économique et respectueuse de l’environnement. Elle est aussi adaptée à la production du composite Pani/BaFe12O19 avec de bonnes propriétés structurales, physiques et magnétiques. L’étude de la substitution du Fe3+ dans le BaFe12O19 par Al3+, Bi3+, Cr3+ et Mn3+ a montré une forte dépendance des propriétés structurales et magnétiques avec la distribution de ces ions dans la maille cristalline hexagonale. En effet, les ions Al3+, Cr3+ et Mn3+ ont une tendance à occuper les sites tétraédriques, alors que le Bi3+ occupe les sites octaédriques. Une augmentation de Hc associée à la taille des cristallites a été observée pour les particules substituées avec l'Al et le Cr alors qu’une modification de l'anisotropie magnetocristalline (fort terme d'ordre supérieur) a été mise en évidence pour les substitutions Bi et Mn, dû à leur grand rayon ionique. L’incorporation des hexaferrites substitués dans la Polyaniline pour obtenir des composites Pani/BaMeFe11O19, où Me = Al, Bi, Cr et Mn, révèle une variation des propriétés électromagnétiques dans la gamme de fréquences allant de 1 à 18 GHz. En effet, ces variations sont dues à la formation de dipôles entre l’ion de substitution et les cations O2- dans le ferrite qui sont responsables de la résonance ferromagnétique, de l'anisotropie magnétocristalline et des interactions avec la matrice polymérique. Le composite Pani/BaFe12O19 présente des absorptions dans la bande X qui se déplacent vers la bande Ku avec la substitution du fer confirmantThis thesis deals with the formulation of Polyaniline/hexaferrite nanocomposite for absorbing electromagnetic waves. The main idea is the process of composite materials based on polymers intrinsic conductors such as polyaniline that we doped with different types of acids (HCl, CSA, NSA, and ... TSA) and barium hexaferrite with magnetoplumbite structure with or without substitution according to desired stoichiometries. In the barium hexaferrite, the substitution of Fe 3+ is made by Al3+, Bi3+, Cr3+ and Mn3+ ions.The barium hexaferrite and its substitutions by different ions mentioned above were synthesized dynamic hydrothermal method by varying various parameters during the synthesis (pH, temperature, time, ratio [OH-]/[NO3-] ...).The elaboration of polyaniline/hexaferrite composite (pure or substituted) was carried out by oxidative polymerization using various synthesis techniques: Aqueous-Based Polymerisation with or without agitation (taking into account the nature of the acid used) (ABP) and Solid-Based Polymerization (SBP). The optimization of these various synthesis techniques after physicochemical (XRD, FTIR, TGA, SEM, EDX), dielectric (ε ', ε' ', σdc) and magnetic (Mr, Ms, Hc, Tc, µ', µ'') characterizations of the samples showed that the solid route is the easiest method, economical and environmentally friendly. It is also suitable for the production of composite Pani/BaFe12O19 with good structural, physical and magnetic properties.The study of the substitution of Fe 3+ in the BaFe12O19 by Al3+, Bi3+, Cr3+ and Mn3+ showed a strong dependence of the structural and magnetic properties with the distribution of these ions in the hexagonal crystal lattice. In fact, Al3+, Cr3+ and Mn3+ ions tend to occupy the tetrahedral sites, while the Bi3+ favoured the octahedral sites. An increase in Hc associated with the small crystallite size observed for particles substituted with Al and Cr and the enhancement magnetocristalline anisotropy (strong higher order term) for Bi and Mn due to their high ionic radius.The incorporation of the substituted hexaferrite in the polyaniline to obtain Pani/BaMeFe11O19 composite, where Me = Al, Bi, Cr and Mn, reveals a variation in electromagnetic properties in the frequency range from 1 to 18 GHz. In fact, these variations are due to the formation of dipoles between the substituting ion and surrounding O2- cations in the ferrite which are responsible for the ferromagnetic resonance, the magnetocrystalline anisotropy and the exchange interaction with the polymer. The composite Pani/BaFe12O19 shows absorption bands at the X-band that shift to the Ku-band with the substitution of iron, confirming the potential of these materials for microwave applications
2
Barbosa, Andreia Guedes Santiago. "Estudo de microestruturas magnéticas por microscopia de força magnética." CNEN - Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, 2010. http://www.bdtd.cdtn.br//tde_busca/arquivo.php?codArquivo=132.
Full textAbstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorA manipulação e o controle das propriedades magnéticas de materiais com pequenas dimensões tem atraído interesse crescente nos últimos anos. Para sistemas magnéticos micrométricos ou submicrométricos, diferentes configurações magnéticas são energeticamente acessíveis. Vórtices magnéticos merecem destaque entre essas configurações e figuram em um grande número de pesquisas tecnológicas que vão desde o armazenamento magnético (VMRAM) até a biofuncionalização de estruturas para o tratamento do câncer. Em uma configuração de vórtice magnético, a energia magnetostática é minimizada por uma configuração de caminho fechado no plano do filme e uma região central com magnetização perpendicular à superfície. A quiralidade (sentido de rotação da magnetização no plano) e a polarização (direção da magnetização na região central) são os dois principais parâmetros que caracterizam um vórtice magnético. Apesar do esforço recente, ainda não se alcançou um entendimento detalhado que permita a manipulação controlada dessas características. Um aspecto importante para a aplicação tecnológica das estruturas de vórtice magnético é a uniformidade e a reprodutibilidade do comportamento de inversão de magnetização da partícula. O tamanho do núcleo do vórtice e o valor da magnetização, fatores que dependem fortemente da anisotropia do sistema, são aspectos relevantes a serem considerados para que as aplicações destas estruturas magnéticas se tornem realidade. Neste trabalho, arranjos regulares de discos multicamadas Co/Pt com diâmetro de 1 e 2 μm e pemalloy com diâmetro na faixa de 5 a 17 μm, ambos com espessura nanométrica, foram investigados por Microscopia de força magnética (MFM) e magnetometria (VSM e PPMS). Um dos objetivos foi investigar a correlação entre a anisotropia magnética nas multicamadas e o tamanho do núcleo do vórtice magnético. Os resultados obtidos demonstraram a presença de estados de vórtice magnético em algumas das amostras estudadas, em função do diâmetro do disco. Além disso, foram estudadas propriedades magnéticas da configuração de vórtices magnéticos desde a nucleação à aniquilação e efeitos de variação de dimensões de disco (diâmetro e espessura) e anisotropia magnética (multicamadas Co/Pt).
The manipulation and control of magnetic properties in size reduced materials have attracted a great interest in the last years. For micrometric or submicron magnetic structures different magnetic configurations are energetically accessible. Magnetic vortex noteworthy belongs to those configurations, and often represents the lowest energy configuration. Nowadays, it appears in a number of technological research ranging from the magnetic storage (VRAM) to the biofunctionalized microdisks for cancer treatment. In a magnetic vortex configuration, magnetostatic energy is minimized by in-plane closed flux domain structure and this curling magnetization turns out of the plane at the centre of the vortex structure. The chirality (direction of rotation of the in-plane magnetization) and polarization (up or down direction of the vortex core) are two topological features that characterize a magnetic vortex. In spite of the great effort on this matter, a controlled manipulation of magnetic vortex features was not reached. A critical aspect for the technological application of magnetic vortex structures is the uniformity and reproducibility of the reversal behavior of the particle magnetization. The vortex core size and the related value of its overall magnetization are also very relevant for the use of such magnetic structures. It is usually considered that the size of the vortex core depends on parameters such as anisotropy, thickness and diameter of the magnetic disk. In this work, regular arrays of Co/Pt multilayers disks with diameter of 1 and 2 μm and pemalloy disks with diameter in the range 5 -17 μm, both nanometer-thick, were investigated by Magnetic Force Microscopy (MFM) and magnetization measurements (VSM and PPMS). The results show the existence of magnetic vortex states for the samples, depending on the disk diameter. Furthermore, it was investigated the magnetic properties of the magnetic vortex, since the nucleation to annihilation, and the effect of variation of disk dimensions (diameter and thickness) and magnetic anisotropy (Co/Pt multilayers).
3
Dudchenko, N. O., A. B. Brik, Y. V. Kardanets, and O. E. Grechanivskyy. "Influence of Ultrasound Treatment on the Properties of Synthetic Magnetite Nanoparticles." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35186.
Full textAbstract:
The paper describes creation of magnetite nanoparticles under ultrasound treatment and investigation
of their phase composition and magnetic properties. Magnetite nanoparticles were synthesized via coprecipitation
of Fe+2 and Fe+3 with KOH in aqueous solution at 80°C. It was shown, that ultrasound treatment
of solution during the synthesis of magnetite nanoparticles leads to the increasing of size and saturation
magnetization obtained nanoparticles. The results of X-ray diffraction measurements show that the
synthesized particles consist of magnetite. The size of synthesized magnetite nanoparticles according to Xray
diffraction measurements was approximately 10 nm. Saturation magnetization of synthesized magnetite
nanoparticles is rather high (37 A*m2/kg). Synthesized magnetite nanoparticles are promising for different
medical-biological applications.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35186
4
Harrison, Richard John. "Magnetic properties of the magnetite-spinel solid solution." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603779.
Full textAbstract:
The intrinsic magnetic properties of Fe-bearing solid solutions with the "spinel" crystal structure are determined to a large extent by the processes of non-convergent cation ordering and subsolvus exsolution. The aim of this dissertation is to investigate the interaction between these processes and the magnetic properties of the magnetite-spinel solid solution, with a view to assessing how these factors might influence the acquisition of natural remanent magnetization in other Fe-bearing solid solutions. Temperature and compositional variations in the state of non-convergent cation order are determined using a macroscopic thermodynamic theory, which is calibrated using cation ordering and phase equilibrium constraints from the literature. The cation distribution in the solid solution is calculated for various temperatures and used to derive the ideal variation in saturation magnetization as a function of composition. A compensation point is predicted at approximately 70 mol% MgA12O4, which is confirmed by experimental measurement of the saturation magnetization in synthetic samples. The magnetic properties of synthetic samples are sensitive to rapid changes in the distribution of Fe2+ and Fe3+ cations which occur during quenching. The kinetics of this ordering process are investigated using the Ginzburg-Landau rate law, which is used to calculate the ordering behaviour during quenching, isothermal annealing and temperature ramp experiments. The calculations show that rapid relaxation of the Fe2+-Fe3+ distribution occurs when intermediate members of the solid solution are heated above 400°C, and there is hysteresis in the degree of order during repeated heating and cooling cycles. Both these effects are confirmed by measurements of magnetic susceptibility versus temperature.
5
Xu, Ming. "Critical current density and time-dependent magnetization of the high transition temperature superconductors." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/30033.
Full text
6
Felton, Solveig. "Tunable Magnetic Properties of Transition Metal Compounds." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5939.
Full text
7
Raanaei, Hossein. "Tailoring Properties of Materials at the Nanoscale." Doctoral thesis, Uppsala : Uppsala University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-107425.
Full text
8
Svensson, Jacob N. "A Study of the Magnetic Properties of Yb4LiGe4: Unusual Magnetism." Thesis, Boston College, 2010. http://hdl.handle.net/2345/1376.
Full textAbstract:
Thesis advisor: Michael GrafThe R5T4 compounds (R = rare earth, T = Ge or Si) are interesting because the magnetic properties are very sensitively dependent on slight changes in the crystalline structure. Yb5Ge4 is one such compound, with (presumed) antiferromagnetic order occurring at TN = 1.7 K. We are interested in the effects of substituting Li in place of one Yb atom. Previous measurements of the magnetic properties of polycrystalline Yb4LiGe4 using NMR, specific heat, and resistance measurements at temperatures down to 0.5 K and in magnetic fields up to 4 Tesla were made to compare results with the parent compound. The resistance measurements showed a maximum at 1.1 K, which may indicate the onset of magnetic order. Thus we performed μSR measurements on Yb4LiGe4 and Yb5Ge4, and analysis of the data confirmed magnetic ordering (possibly antiferromagnetic) at 1.1 K. The μSR measurements also revealed a dependence on the magnetic history of the sample. Currently we are studying the pressure dependence of the (presumed) Néel Temperature in order to explore whether increased pressure can drive the TN to 0 K, and results will be discussed
Thesis (BS) — Boston College, 2010
Submitted to: Boston College. College of Arts and Sciences
Discipline: Physics Honors Program
Discipline: Physics
9
Han, Man Huon. "Development of synthesis method for spinel ferrite magnetic nanoparticle and its superparamagnetic properties." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26465.
Full textAbstract:
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.Committee Chair: Z. John Zhang; Committee Member: Angus Wilkinson; Committee Member: C P Wong; Committee Member: E. Kent Barefield; Committee Member: Mostafa El-Sayed. Part of the SMARTech Electronic Thesis and Dissertation Collection.
10
Virdee, D. "The influence of magnetostatic interactions on the magnetic properties of magnetite." Thesis, University of Edinburgh, 1999. http://hdl.handle.net/1842/14612.
Full textAbstract:
The effect of magnetostatic interactions on the magnetisation structure and magnetic properties of magnetite grains for the size range 0.03 - 0.15 microns has been examined. The understanding of magnetostatic interactions is important because magnetite that occurs naturally by some precipitation process and in sedimentary rocks containing magnetosomes may form as magnetostatic interacting clumps of grains. This has implications in the way we perceive magnetic signals are recorded in rocks, bacterial magnetosomes found in sedimentary rocks, and also in magnetic recording media. The examination of magnetostatic interactions has been achieved by using a three-dimensional micromagnetic model which considers arrays of 4x4x4 cubic magnetite grains with uniaxial shape anisotropy and arrays of 6x6 or 4x4 cubic grains, arranged analogous to arrays of particles that may be produced by a method of electron beam lithography. The grains have a maximum spacing of one grain width, when they are seen to be non-interacting: or a minimum where they are almost touching, when they are interacting. Using this method it is possible to see how grain interactions alter the magnetic domain structure of uniform and non-uniform grains. The effect of interactions on bulk properties, such as coercivity and remanence can be examined from simulated hysteresis cycles. Properties are examined when the grains are arranged within the arrays such that their easy axes of magnetocrystalline anisotropy are aligned parallel with every other grain in the array, and in the case where the axes are in a randomly differing orientation from every other grain within the array. Hysteresis parameters for non-interacting and interacting arrays of grains are calculated, and these theoretical values are compared with previous theoretical micromagnetic models and experimental work. The results from this study are in good agreement with previous work.
11
Newcombe, Lee. "The effects of screw dislocations on the magnetic properties of magnetite." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/15500.
Full textAbstract:
The values of the hysteresis parameters produced by micromagnetic models are usually lower than those found experimentally, and in the case of grains which have been subjected to stress the simulated values can be as much as an order of magnitude too low. It has been suggested that the presence of crystalline defects within these stressed grains may be responsible for raising the coercivity and saturation remanence values in comparison with unstressed grains. Grains of magnetite containing a regular array of screw dislocations are modelled for different grain sizes and different dislocation densities using a micro-magnetic model which considers the exchange, demagnetising, magnetoelastic, magnetocrystalline anisotropy and external field interactions. It is found that the values obtained from the new model for coercivity and saturation remanence rise with increasing dislocation density in line with experimental results. Models containing dislocations are found to have the magnetic properties of defect-free grains of smaller grain size, again in line with experiment. The unblocking temperature of a 1μm grain of magnetite in zero applied field is found to decrease in an approximately linear manner with increasing dislocation density. This thesis shows that by considering the magnetoelastic energy arising from the presence of screw dislocations the discrepancy between the hysteresis parameters of magnetite obtained theoretically and experimentally may be resolved.
12
Mukherjee, Paromita. "Investigation of the magnetic and magnetocaloric properties of complex lanthanide oxides." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275425.
Full textAbstract:
Complex lanthanide oxide systems are known to host novel phases of matter, while also providing functionality for practical applications. In this dissertation, the structural, magnetic and magnetocaloric properties of three families of lanthanide oxides have been studied with the dual aims of investigating the magnetic behaviour and identifying promising magnetic refrigerants for cooling to temperatures currently accessible using non-renewable liquid He. The thesis presents a two-part study of the magnetic and magnetocaloric properties of the geometrically frustrated lanthanide garnets, where the magnetic $Ln^{3+}$ form corner-sharing triangles. First, the family of garnets $Ln_3A_2X_3$O$_{12}$, $Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li are investigated. Changes to the single-ion anisotropy of the magnetic ion as well as variations in the chemical pressure radically alters the nature of magnetic ordering, the degree of frustration and the magnetocaloric performance. In the second part, the garnets $Ln_3A$Ga$_4$O$_{12}$, $Ln$ = Gd, Tb, Dy, Ho, $A$ = Cr, Mn, are studied. Introducing additional spins significantly reduces the frustration in the garnet lattice. Low temperature powder neutron diffraction of Ho$_3$MnGa$_4$O$_{12}$ reveals concomitant ordering of Ho$^{3+}$ and Mn$^{3+}$ moments below the ordering temperature, $T_N$ = 5.8 K. The magnetocaloric performance of $Ln$_3CrGa$_4$O$_{12}$, $Ln$ = Gd, Dy, Ho, greatly surpasses that of the parent $Ln_3$Ga$_5$O$_{12}$ at $T$ = 2 K. The final results chapters in the thesis describe the magnetism and magnetocaloric effect in the lanthanide orthoborates, $Ln$BO$_3$ , $Ln$ = Eu, Gd, Tb, Dy, Ho, Er, Yb and the lanthanide metaborates, $Ln$(BO$_2$)$_3$, $Ln$ = Pr, Nd, Gd, Tb. The magnetic $Ln^{3+}$ form slightly distorted edge-sharing triangular layers in $Ln$BO$_3$. Unique magnetic features are observed, including short-range ordering and spin reorientation transitions depending on the single-ion anisotropy of the $Ln^{3+}$. The $Ln$BO$_3$ are also efficient magnetocalorics in the liquid helium temperature range. The lanthanide metaborates contain one-dimensional chains of magnetic lanthanide ions. Bulk magnetic measurements show features consistent with low-dimensional magnetism, such as magnetisation plateaux at one-third of the saturation magnetisation for Nd(BO$_2$)$_3$ and Tb(BO$_2$)$_3$ in a field of 14 T. This thesis provides insight into the fundamental magnetic properties of complex lanthanide oxide systems and also demonstrates strategies for identifying new magnetocaloric materials: both through chemical control of the structure of well-known magnetocalorics and by studying materials that have not been explored previously. The results pave the way for further in-depth investigations and finding new magnetic coolants based on complex lanthanide oxide systems.
13
Mokhtari, Abbas. "On the growth, magnetic properties and Magneto-Optical Studies of ZnO based Dilute Magnetic Semiconductors and Magnetite." Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500218.
Full text
14
Diaz, Begoña Ruiz. "Magnetic properties of granular magnetic materials." Thesis, University of York, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428429.
Full text
15
Anderson, Richard M. "Magneto-optical properties of superparamagnetic spinel ferrite nanoparticles." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/30027.
Full text
16
Lakay, Eugene Marlin. "Superparamagnetic iron-oxide based nanoparticles for the separation and recovery of precious metals from solution." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1866.
Full text
17
Thomson, Leslie Campbell. "A three-dimensional micromagnetic investigation of the magnetic properties and structures of magnetite." Thesis, University of Edinburgh, 1993. http://hdl.handle.net/1842/13127.
Full textAbstract:
This work is a three-dimensional micromagnetic study of the magnetic properties and structures of magnetite. Large magnetite crystals in the size range 10 - 50 μm were modelled using a relatively low resolution model. The vortex configuration was found to be stable for this size range. A flower type structure was also obtained with large, uniformly magnetised domains lying approximately in magnetocrystalline easy directions as in figure 6.1. A global optimisation algorithm called simulated annealing (SA) was used to minimise the total free magnetic energy and hence find stable structures for crystals in the sub-micron size range. The resolution of the model was limited by computer constraints when using SA for optimisation. The structures obtained were interpolated to a higher resolution and input as the initial configuration for a fast local optimisation technique called the conjugate-gradient method. This combination of techniques allowed high resolution models in the ground state configuration to be obtained. Below 0.06μm, nearly uniform structures magnetised in the magnetocrystalline easy directions were obtained. Between 0.06 μm and 1.0μm, only the vortex configuration was obtained. These are the lowest energy states found by any method to date. A modified SA algorithm was used to introduce thermal fluctuations into a micromagnetic model, and hence to determine blocking temperatures of grains up to 0.1 μm in size. The model gave results consistent with Néel's single domain thermoremanent magnetisation theory for grains up to 0.065 μm. Between this size and 0.07 μm a reduction in blocking temperature was observed to take place for cubic grains.
18
Haynes, John Stephen. "Spectroscopic and magnetic properties of pyridine and pyrazine complexes of divalent iron and copper." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25821.
Full textAbstract:
Magneto-structural correlations have been made for a number of pyridine and pyrazine complexes of iron(II) and copper(Il), involving anions of a range of coordinating abilities, for example, sulfonate, RS0₃⁻ (where R is CF₃, CH₃ or p-CH₃C₆H₄); halide, Cl⁻ Br⁻ or I⁻; pseudohalide, NCO⁻ or NCS⁻; perchlorate and hexafluoroarsenate. Structure was determined by infrared, electronic and Mössbauer spectroscopy and differential scanning calorimetry, and, in some instances, by single-crystal X-ray diffraction. Spectroscopic results were used to investigate the nature of both anion and neutral ligand coordination.
In complexes of stoichiometry ML₄ (RS0₃)₂ (where M is Fe or Cu, L is pyridine, pyrazine or 2-methylpyrazine and R is CF₃, CH₃ or p-CH₃C₆H₄), the neutral ligands were found to adopt a unidentate mode of coordination. For several of these complexes, X-ray crystallography revealed a square-planar array of pyridine ligands around the central metal, with anions coordinated in a unidentate mode above and below this plane. A monomeric molecular structure results in which the paramagnetic centres are well isolated from each other giving rise to magnetically-dilute species.
In complexes of stoichiometry M(pyz)₂X₂ (where M is Fe or Cu and X⁻ is CF₃S0₃⁻, CH₃S0₃⁻, Cl⁻, Br⁻, I⁻, C10₄⁻ or NCS⁻), pyrazine was found to coordinate through both nitrogen donor atoms and inorganic coordination polymers were produced. X-ray crystallography revealed a two-dimensional lattice in Cu(pyz)₂(CH₃S0₃)₂ with two distinct kinds of bridging pyrazine groups and monodentate sulfonate anions. For the remaining bis(pyrazine) complexes, spectroscopic evidence supports similar structures with unidentate anion coordination and bidentate
bridging pyrazine ligands leading to sheet-like polymers. Cu(pyz)₂(CH₃S0₃)₂ and Fe(pyz)₂(NCS)₂ exhibit magnetic susceptibilities which reveal the antiferromagnetic nature of these materials (ˣmax at temperatures of 7.0 and 8.0 K respectively); the data were analysed in terms of a two-dimensional Heisenberg model. For the copper complex, in which the structure shows stronger pyrazine coordination along one dimension, the data were also analysed in terms of a linear chain model. Mössbauer spectroscopy showed Fe(pyz)₂(NCS)₂ to undergo a transition to a magnetically-ordered state at 9.2 K. The magnitude of the exchange coupling through bridging pyrazine in Fe(pyz)₂X₂ complexes (where X⁻ is CF₃S0₃⁻, CH₃S0₃⁻, Cl⁻, Br⁻, I⁻ or C10₄⁻) is considerably less than that present in either Cu(pyz)₂(CH₃SO₃)₂ or Fe(pyz)₂(NCS)₂.
Spectroscopic evidence indicates that for Fe(py)₂(CF₃S0₃)₂ and complexes of stoichiometry M(pyz)X₂ (where M is Fe or Cu and X⁻ is CF₃S0₃⁻, p-CH₃C₆H₄S0₃⁻, Cl⁻ or NCO⁻) bridging anionic ligands are present and for the mono(pyrazine) complexes the neutral ligand also coordinates in a bridging mode. Fe(pyz)(CF₃S0₃)₂, Fe(pyz)(NCO)₂ and Cu(pyz)(CF₃SO₃)₂ all exhibit magnetic susceptibility data characteristic of antiferromagnetic materials (ˣmax at temperatures of 4.4, 38 and 7.0 K respectively). The magnetic susceptibilities for these materials were analysed in terms of the two-dimensional Heisenberg model and a linear chain model. Mössbauer spectroscopy shows both Fe(pyz)(CF₃S0₃)₂ and Fe(pyz)(NCO)₂ to undergo a transition to long-range magnetic ordering at temperatures of 3.9 and 27.0 K respectively.
Low-temperature (4.2-130 K) magnetic susceptibility measurements for the iron(II) sulfonate compounds, Fe(RS0₃)₂ (where R is F, CF₃, CH₃ or p-CH₃C₆H₄) are reported. For the compounds where R is F, CF₃ or p-CH₃C₆H₄ the magnetic moment data were assessed in terms of crystal-field splitting effects. The magnetic moment data for ɑ and β forms of Fe(CH₃S0₃)₂ are indicative of antiferromagnetic exchange interactions and the characteristics of the susceptibility curve for the β isomer are explained on the basis of a transition from short-range to long range three-dimensional magnetic ordering at 22 K.Science, Faculty of
Chemistry, Department of
Graduate
19
Taylor, Anthony Park 1963. "Terbium iron cobalt diffusion barrier studies." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276931.
Full textAbstract:
Thin films (5nm ± 2nm thick) of ZrO2, Al2O3, TiO2, Sm, Gd, Zr, Ni, and Pt were deposited onto TbFeCo films (100nm ± 20nm thick) on silicon and graphite substrates and analyzed with XPS as prospective candidates for TbFeCo diffusion barriers. Metals were chosen primarily according to electronegativity. Samples were typically heated to 272°C in UHV for 20 hours to enhance diffusion. Experiments with the metals were performed in a more consistent manner than with the oxides. The Sm, Gd, and Zr were reactively oxidized during the deposition. The Sm/Sm-oxide and Gd/Gd-oxide appeared to be favorable candidates for TbFeCo diffusion barriers. TbFeCo was not detected near the surface before or after heating the samples to 272°C for 20 hours and depth profiles indicated oxygen contamination decreased steadily as the barrier/TbFeCo interface was approached. For the other materials examined, either the oxides were reduced (at least partially) during heating to 272°C (381°C for Al₂O₃) or diffusion of TbFeCo was detected after heating, indicating that they would not be favorable candidates for TbFeCo diffusion barriers.
20
Mahon, Stephen William. "Magnetic properties of ceramics." Thesis, University of Newcastle Upon Tyne, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358891.
Full text
21
Bertrand, Renee. "Magnetic properties of asbestos." Thesis, Open University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235729.
Full text
22
Sepioni, Margherita. "Magnetic properties of graphene." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/magnetic-properties-of-graphene(61e2c890-e044-4762-a9b5-a6bef2d5b545).html.
Full textAbstract:
Graphene – a monolayer of carbon atoms densely packed in a honeycomb lattice – was isolated for the first time in 2004 and, since then, has established itself as one of the most remarkable materials available to condensed matter scientists today. Theory predicts a whole spectrum of magnetic phenomena in graphene, including several mechanisms for intrinsic ferromagnetism and spin-ordering effects that arise due to its low-dimensionality and highly unusual electronic properties (e.g. Dirac-like spectrum). In this experimental work, SQUID (Superconducting Quantum Interference Device) magnetic measurements have been carried out in graphene laminates with masses up to ≈ mg obtained by ultrasonic exfoliation of highly oriented pyrolytic graphite (HOPG) in N-methyl-pyrrolidone (NMP). Scanning electron microscopy (SEM) and X-ray diffraction experiments revealed that the laminates are made of decoupled graphene crystallites with typical flake size below 50 nm. Atomic force microscopy (AFM) measurements carried out for graphene suspensions dispersed onto a SiO2 substrate allowed the recognition of thin crystallites associable to single and double-layer graphene. X-ray dispersive fluorescence (XRF) and electron dispersive diffraction (EDX) confirmed the laminates chemical purity with absence of metals and/or magnetic inclusions. Pristine laminates exhibit Curie paramagnetism noticeable below ≈ 50 K, which contributes to about one moment per crystallite at 2 K. The laminates are strongly diamagnetic, although a decrease of the diamagnetic susceptibility by about three times with respect to graphite was observed for fields applied perpendicularly to the ab plane. The same graphene laminates were employed as a reference system to study magnetism of point defects, such as fluorine adatoms and vacancies generated through ion irradiation. The unambiguous spin value J=1/2 found for both species of defects confirms theoretical expectations. In the case of fluorine atoms a magnetic moment of 1 µB per ≈ 1000 adatoms was obtained, associated to the tendency of fluorine to cluster in graphene. Vacancies produced a value of the magnetic moment much closer to the expected 1 µB for point defects. No sign of defect related ferromagnetism was observed. On the other hand, our study performed on NT-MTD HOPG crystals (the same adopted for the fabrication of our graphene laminates), revealed ferromagnetic signals up to 3∙10-3 emu/g. Backscattering electron microscopy (BSE), performed alongside EDX chemical analysis, confirmed that the observed magnetic behaviour is due to ferromagnetic inclusions, such as magnetite and titano-magnetite. Therefore, weak and poorly reproducible ferromagnetic-like signals in graphene laminates were attributed to the same contaminations present in the original material (i.e. HOPG).
23
Dempsey, Kari Jacqueline. "Magnetic and electronic transport properties of magnetic nanoparticles." Thesis, University of Leeds, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534426.
Full text
24
Vestal, Christy Riann. "Magnetic couplings and superparamagnetic properties of spinel ferrite nanoparticles." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-06072004-131405/unrestricted/vestal%5Fchristy%5Fr%5F200405%5Fphd.pdf.
Full text
25
Moro, Ramiro Alfredo. "Ferroelectricity in free niobium clusters." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04062004-164744/unrestricted/moro%5Framiro%5Fa%5F200312%5Fphd.pdf.
Full text
26
Wang, Huabin 1969. "The magnetic properties, crystal and magnetic structures of Nd5SixGe4-x /." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101661.
Full textAbstract:
The magnetic properties, crystal and magnetic structures of Nd5 SixGe4-x were investigated by ac susceptibility and high resolution neutron powder diffraction. The magnetic and crystalline phase diagrams were derived. Four distinct structures exist in the Nd 5SixGe4-x system: Gd5Ge 4-type [O(II)], Gd5Si2Ge2-type (M), Gd5Si4-type [O(I)], and Zr5Si4-type (T). The refinements of the neutron powder diffraction patterns revealed that the Nd5SixGe4-x compounds exhibit mixed ferro-antiferromagnetic structures. The ac susceptibility measurements showed that the magnetic ordering temperature of Nd5SixGe 4-x increases slightly with increasing silicon content, except that it increases by a factor of 2 in the orthorhombic Gd5Si 4-type [O(I)] phase region. The abrupt change of the magnetic ordering temperature between x = 2.25 and x = 2.5, where the monoclinic Gd5Si 2Ge2-type (M) structure changes to the orthorhombic Gd 5Si4-type [O(I)] structure, suggested that a first order magnetostructural transition likely takes place in this narrow composition range (2.25 < x < 2.5). The investigation of Nd5Si2.335 Ge1.665 revealed that Nd5Si2.335Ge 1.665 adopts the Gd5Si2Ge2-type (M) structure and undergoes a first order magnetostructural transition from the paramagnetic-monoclinic Gd5Si2Ge2-type (M) structure to the orthorhombic Gd5Si4-type [O(I)] structure upon cooling. The T1-T1 bonds increases by ∼1 A when the the Gd 5Si4-type [O(I)] structure (10 K) transforms to the Gd 5Si2Ge2-type (M) structure (140 K). The giant magnetocaloric effect is not observed in Nd5Si2.335Ge 1.665 probably due to the co-existence of the M phase and the O(I) phase. The maximum magnetic entropy change in Nd5Si2.335Ge 1.665 is 7.3 J/kg K for magnetic field change from 0 to 7 Tesla, which is similar to that obtained in Nd5Si1.5Ge2.5, the neighboring phase O(I).
27
Hsu, Chia-Hao. "Optimizing the thermal material in the thermally actuated magnetization (TAM) flux pump system." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648197.
Full text
28
Sakhnini, Lama Issam. "The microwave, optical and magnetic properties of magnetic fluids." Thesis, Bangor University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385796.
Full text
29
Alper, Muersel. "Electrodeposited magnetic superlattices : (growth, characterization, magnetic and magnetotransport properties)." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261317.
Full text
30
Zubarev, A. Yu, D. N. Chirikov, D. Yu Borin, and G. V. Stepanov. "Hysteresis of the magnetic properties of soft magnetic gels." Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A36414.
Full textAbstract:
We present results of an experimental and theoretical study of the magnetic properties of soft magnetic gels consisting of micron-sized magnetizable particles embedded in a polymer matrix. Experiments demonstrate hysteretic dependences of composite magnetization on an applied magnetic field and non-monotonic, with maximum, dependence of the sample susceptibilities on the field. We propose a theoretical approach which describes the main physical features of these experimental results.
31
Schelter, Eric John. "Cyanide clusters of ReII with 3d metal ions and their magnetic properties: incorporating anisotropic ions into metal-cyanide clusters with high spin magnetic ground states." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/2205.
Full textAbstract:
Clusters of metal ions that possess large numbers of magnetically coupled unpaired electrons have attracted much interest in recent years due to their fascinating magnetic behavior. With an appreciable component of magnetic anisotropy, these large-spin paramagnetic molecules can exhibit an energy barrier to inversion of their magnetic dipole, leading to spontaneous magnetization and magnetic hysteresis below a critical temperature. Since this behavior is a property of an individual clusters rather than a collection of molecules, this phenomenon has been dubbed ??Single Molecule Magnetism??. Our approach to the study of new high-spin systems has been to exert a measure of synthetic control in the preparation of clusters. Specifically we are employing highly anisotropic metal ions with the anticipation that these ions would engender large overall magnetic anisotropy in the resulting clusters. The first step in this process was the development of the chemistry of two new d5 ReII (S = ??) complexes, namely [ReII(triphos)(CH3CN)3][PF6]2 and [Et4N][ReII(triphos)(CN)3]. The magnetic, optical and electrochemical properties were studied and theoretical models were developed to describe the origin of the large temperature independent paramagnetism that was observed. Next, we successfully employed transition metal cyanide chemistry using the ReII building blocks to prepare a family of isostructural, cubic clusters of the general formula {[MCl]4[Re(triphos)(CN)3]4} M = Mn, Fe, Co, Ni, Cu, Zn whose 3d ions adopt local tetrahedral geometries. Within the clusters, magnetic exchange is observed between the paramagnetic ions, which has been modeled using an Ising exchange model to account for the dominating anisotropy of the ReII ion. Despite the high pseudo-symmetry of the clusters (Td), this work has yielded a rare example of a metal-cyanide single molecule magnet, {[MCl]4[Re(triphos)(CN)3]4} with an S = 8 ground state, D = -0.39 cm-1 and an effective energy barrier for magnetization reversal of Ueff = 8.8 cm-1. The elucidation of this family of isostructural clusters has also allowed us to pursue fundamental work on the structure/property relationships of the exotic, paramagnetic ReII ion. As the clusters are soluble, stable compounds, the future of this chemistry lies in the development of a true building-block approach to ??super-clusters?? that exhibit very high ground state spin values.
32
Brandl, Ana Lucia. "Propriedades magnéticas de sistemas nanocristalinos." [s.n.], 2004. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278234.
Full textAbstract:
Orientador: Marcelo KnobelTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-04T01:56:42Z (GMT). No. of bitstreams: 1 Brandl_AnaLucia_D.pdf: 5290468 bytes, checksum: 32290a7675f89cf9c2a2ea53be70c6fb (MD5) Previous issue date: 2004
Resumo: Sistemas magnéticos granulares são constituídos de pequenas partículas magnéticas imersas numa matriz não magnética. Essas partículas têm formas e tamanhos variados, eixos de anisotropia variados e orientados aleatoriamente e, dependendo do tipo de matriz (isolante ou condutora) e da concentração do material magnético, diferentes tipos de interações magnéticas podem estar presentes. Esses materiais apresentam diversas propriedades físicas interessantes, como magneto-resistência gigante e efeito Hall gigante. Devido à complexidade desses sistemas, a sua magnetização só pode ser calculada analiticamente em dois casos limites: quando a temperatura é zero (modelo Stoner-Wohlfarth) ou quando a temperatura é alta (modelo de Langevin). Embora o modelo de Langevin seja aplicado com bastante sucesso para temperaturas acima da temperatura de bloqueio média (TB) do sistema, mostramos nesse trabalho que os resultados podem ser enganosos, fornecendo parâmetros estruturais muito diferentes dos reais. Essas discrepâncias podem ser atribuídas a efeitos de interações magnéticas e a efeitos de anisotropia, ambos desconsiderados no formalismo de Langevin. Os principais resultados experimentais apresentados nesta dissertação foram obtidos de um conjunto de filmes granulares do tipo metal-isolante, com partículas nanocristalinas de Co imersas numa matriz amorfa de SiO2, fabricados por evaporação catódica. A caracterização magnética foi realizada através de medidas de magnetização em função do campo, susceptibilidade resfriada com e sem campo magnético aplicado e magnetização termo-remanente. A caracterizção estrutural foi realizada através de medidas de microscopia de transmissão de elétrons, difração de raio-x e espalhamento de raio-x a baixo ângulo
Abstract: Granular magnetic systems are formed by magnetic grains whose size is of the order of a few nanometers, embedded in a non-magnetic (insulating or metallic) matrix. These ultrafine particle systems present size, shape, and anisotropy distributions, besides randomly orientated easy directions. Magnetic interactions always exist, being stronger or weaker according to the volume concentration and the matrix type. These systems have shown interesting magnetotransport properties, as giant magnetoresistance and giant Hall effect. Owing to the inherent complexity of the nanostructure, the magnetization can be analytically calculated only in two limiting cases: when T = 0 (Stoner-Wohlfarth model) or for high temperatures (Langevin model). The Langevin model presents very good results when applied at temperatures higher than the mean blocking temperature (TB) of the system. However this adequacy can be just apparent: the obtained structural parameters are very different from the real ones, as we show in this work. These discrepancies can be attributed to magnetic interactions andanisotropy effects, both unconsidered in the Langevin formalism. The main results presented in this thesis were obtained from a set of metal-insulator granular films, composed of Co nanoparticles immersed in an amorphous SiO2 matrix. The films were produced by magnetron co-sputtering. The magnetic characterization was perfomed with magnetization loops, zero-field cooled and field cooled susceptibilities, and thermoremanent magnetization. The microstructural characterization was done by transmission electron microscopy, x-ray diffraction, and small angle x-ray scattering
Doutorado
Física
Doutor em Ciências
33
Martins, Cezar Soares. "Magnetização e Magnetoresistência Gigante em Ligas Granulares CuNiFe." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-02122013-185104/.
Full textAbstract:
Neste trabalho, estudamos as propriedades magnéticas e a magnetoresistência gigante (GMR) em fitas de Cu IND.80 Ni IND.20-xFe IND.x (x = 2,5 ; 5; 10; 17, 5; 20) produzidas por melt-spinning. As fitas foram estudadas como função da temperatura de tratamento térmico T IND.an 500°C, usando-se um magnetômetro SQUID. Uma grande variedade de estruturas granulares foram obtidas para diferentes razões de Ni/Fe e condições de tratamento térmico. Para Cu80 Ni10 Fe10, a magnetização não apresentou histerese mensurável para T 50K. Este comportamento é consistente com as curvas de susceptibilidade que indicam uma temperatura de bloqueio abaixo de 50K. Nesta temperatura, o maior valor da GMR(19%) foi obtido para as fitas tratadas a 400°C por duas horas. As curvas de magnetização foram comparadas a um modelo teórico que assume uma distribuição de momentos magnéticos. Para Cu80Ni15Fe5,a microestrutura e as propriedades magnéticas são muito sensíveis ao tratamento térmico. Para as ligas com composições 10; 15; 17,5% de Fe, a magnetização de saturação apresentou uma redução com o tratamento a 400°C. Esta redução foi explicada através da formação de partículas perto da região Invar. Um comportamento anômalo linear da amplitude da magnetoresistência foi observado e explicado pelo espalhamento dependente do spin, que acontece quando um elétron se move de uma partícula superparamagnética para uma partícula bloqueada termicamente.In this work, we study the magnetic properties and giant magnetoresistance (GMR) in ribbons of Cu80 Ni20-xFex (x = 2.5, 5, 10, 17.5, 20) prepared by melt-spinning. The ribbons were studied as a function of annealing temperature Tan 500°C, using a SQUID magnetometer. A wide variety of granular structures é obtained for different Ni/ Fe ratios and annealing conditions. In Cu80 Ni10 Fe10 , the magnetization shows no static hysteresis for T 50K. This behaviour is consistent with the susceptibility curve which indicates a blocking temperature below 50K. At this temperature, the largest GMR value was obtained for the ribbons annealed at 400°C for two hours. The magnetization curves were compared with a theoretical model that takes into account the magnetic moment distribution. In Cu80 Ni15Fe5, the microstructure and magnetic properties are much more sensitive to annealing. For t he ribbons with 10, 15, 17.5 % Fe composition, the magnetization presented a reduction with annealing at 400°C. This redution may be explained in terms of particle formation near the Invar region. An anomalous linear behaviour of the MR was observed and can be explained in terms of spin-dependent scattering when an electron passes from a superparamagnetic particle to a thermally blocked particle.
34
Xue, Wei xue. "Measurements of Cellular Intrinsic Magnetism with Cell Tracking Velocimetry and Separation with Magnetic Deposition Microscopy." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461231847.
Full text
35
Rinkevich, A. B., M. I. Samoylovich, and A. F. Belyanin. "Effective Conductivity and Magnetic Permeability of Nanostructured Materials in Magnetic Field." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35340.
Full textAbstract:
The problem of homogenization the nanostructured materials placed in DC magnetic field has been discussed. The experimental data are obtained using metallic superlattices, metal-dielectric thin films and 3D-nanostructured materials. All these materials contain ferro- or ferrimagnetic component. The trans-mission and reflection coefficients were measured on the waves of millimeter waveband. It has been shown that the experimental frequency spectra of the coefficients in zero magnetic field can be described by the effective conductivity and dielectric permittivity. The spectra of ferromagnetic resonance, however, cannot be calculated correctly with the averaged magnetization.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35340
36
Qureshi, Saleem. "Magnetic properties of TCNQ complexes." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278000.
Full text
37
Lloyd, Sion. "The magnetic properties of superconductors." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343847.
Full text
38
Chowdhary, S. K. "Magnetic properties of lunar samples." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353792.
Full text
39
Agrachev, Mikhail. "Fundamental Properties of the Molecular Au Clusters." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3422311.
Full textAbstract:
Monolayer-protected gold clusters (MPCs) are a very interesting and fascinating class of compounds, from the points of view of both the fundamental science and their possible applications. They are composed of a gold core, with a diameter smaller than a few nanometers, and are surrounded by a protecting organo-thiolate monolayer, bonded by covalent Au-S bonds. Due to their dimensions, these systems exhibit properties in between those of molecules and nanoparticles, therefore displaying unique physical and chemical behaviors. In this Thesis, some properties of the most stable and well-known molecular MPC are addressed and studied. The investigation focuses on fundamental features, including solid-state properties, optical behavior, reactivity and especially their magnetic properties. The investigation of the latter constitutes the major part of this work. Particular attention is dedicated to the effect of ligands on these phenomena. The main tool of our investigation was electron paramagnetic resonance (EPR) spectroscopy, which was used to study these MPCs both in solution and in the solid state. The topics addressed are to understand the magnetic interactions between gold core and the capping ligands in solutions phase and ferromagnetic and antiferromagnetic interactions between clusters in the solid state. Another magnetic resonance technique, nuclear magnetic resonance, was used for the study of the ligand exchange kinetics. The data obtained from a number of experimental techniques and computational calculations were used in conjunction with these two main tools.I cluster d’oro protetti da monostrato (MPC) sono una classe di composti molto interessante e affascinante, sia dal punto di vista della ricerca di base, che delle loro possibili applicazioni. Sono composti da un core di oro, con un diametro inferiore a pochi nanometri e sono circondati da un monostrato organo-tiolato, legato con legami covalenti Au-S. A causa delle loro dimensioni, questi sistemi esibiscono proprietà a metà strada fra quelle di molecole e nanoparticelle, mostrando quindi comportamenti fisici e chimici unici. In questa Tesi sono state studiate alcune proprietà del MPC più stabile e conosciuto. L’indagine è stata focalizzata su caratteristiche fondamentali, che includono proprietà di stato solido, comportamento ottico, reattività e in particolar modo le loro proprietà magnetiche. L’indagine di queste ultime costituisce la parte più rilevante di questo lavoro. Un’attenzione particolare è stata dedicata all’effetto dei leganti su questi fenomeni. Lo strumento principale della nostra indagine è stata la spettroscopia di risonanza paramagnetica elettronica (EPR), la quale è stata utilizzata per studiare questi sistemi sia in soluzione che allo stato solido. Gli argomenti trattati sono la comprensione delle interazioni magnetiche fra il core d’oro e i leganti in soluzione e delle interazioni ferromagnetiche e antiferromagnetiche fra cluster allo stato solido. Un’altra tecnica di risonanza magnetica, la risonanza magnetica nucleare, è stata usata per lo studio della cinetica di scambio di leganti. I dati ottenuti da alcune altre tecniche sperimentali e calcoli computazionali sono stati utilizzati in combinazione con questi due strumenti principali.
40
Sabo, Daniel E. "Novel synthesis of metal oxide nanoparticles via the aminolytic method and the investigation of their magnetic properties." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50122.
Full textAbstract:
Metal oxide nanoparticles, both magnetic and nonmagnetic, have a multitude of applications in gas sensors, catalysts and catalyst supports, airborne trapping agents, biomedicines and drug delivery systems, fuel cells, laser diodes, and magnetic microwaves. Over the past decade, an inexpensive, simple, recyclable, and environmentally friendly large, scale synthesis method for the synthesis of these metal oxide nanoparticles has been sought. Many of the current techniques in use today, while good on the small, laboratory bench scale, suffer from drawbacks that make them unsuitable for the industrial scale. The aminolytic method, developed by Dr. Man Han while working for Dr. Zhang, fits industrial scale-up requirements. The aminolytic method involves a reaction between metal carboxylate(s) and oleylamine in a non-coordinating solvent. This system was shown to produce a range of spinel ferrites. Dr. Lisa Vaughan showed that this method can be recycled multiple times without degrading the quality of the produced nanoparticles. The purpose of this thesis is to test the versatility of the aminolytic method in the production of a wide range of metal oxides as well as various core/shell systems. Chapter 2 explores the effect of precursor carboxylates chain length on the aminolytic synthesis of cobalt ferrite, and manganese ferrite nanoparticles. In Chapter 3, a series of CuxMn1-xFe₂O₄, (x ranges from 0.0 to 0.2), nanoparticles were synthesized via the aminolytic method. This series allows for the investigation of the effects of orbital Jahn-Teller distortion as well as orbital angular momentum on the magnetic properties of this ferrite. The quantum couplings of magnetic ions in spinel ferrites govern their magnetic properties and responses. An understanding of the couplings between these metal ions allows for tailoring magnetic properties to obtain the desired response needed for various applications. Chapter 4 investigates the synthesis of MnO and Mn₃O₄ nanoparticles in pure single phase with high monodispersity. To the best of our knowledge, the range of sizes produced for MnO and Mn₃O₄ is the most extensive, and therefore a magnetic study of these systems shows some intriguing size dependent properties. The final part of this chapter investigates the applicability of the aminolytic method for building a MnO shell on a CoFe₂O₄ core. Chapter 5 explores the synthesis of another metal oxide, ZrO₂ in both the cubic and monoclinic phases with no impurities. The use of the aminolytic method here removes the need for dangerous/expensive precursors or equipment and eliminates the need for extensive high temperature heat treatments that destroy monodispersity which is required for most techniques. The creation of a core/shell system between CoFe₂O₄ and ZrO₂ using the aminolytic method was also tested. This core/shell system adds magnetic manipulation which is especially useful for the recovery of zirconia based photocatalyst. Chapter 6 studies the application of the aminolytic method in the synthesis of yttrium iron garnet (YIG) and yttrium iron perovskite (YIP) nanoparticles. Current synthesis techniques used to produce YIG and YIP nanoparticles often requires high temperatures, sensitive to contamination, which could be eliminated through the use of our method
41
Soroka, Inna. "Magnetic Heterostructures : The Effect of Compositional Modulation on Magnetic Properties." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5733.
Full text
42
Horsfall, Alton Barrett. "Electrical and magnetic properties of II-VI diluted magnetic semiconductors." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4984/.
Full textAbstract:
The electrical and magnetic properties of MOVPE grown epitaxial layers of Hg(_1-x)Mn(_x)Te layers has been investigated using a number of techniques. The samples have been grown by the Inter Diffused Multilayer Process, (IMP) on (100) semi insulating GaAs substrates with ZnTe and CdTe buffer layers. The samples have been shown to show a number of phenomena nopt observed in the bulk material, such as an anomaly in the resistivity, rnagnetoresistance related to the intrinsic magnetism of the material, and saturation of the room temperature magnetisation. In general the samples are of a highly compensated nature with the value of |R(_H)e|(^-1) varying between l0(^14) and 5xI0(^17) cm(^-3) at 20K, the Hall mobilities varying between 8 and 3.5x10(^5) cm(^2)V(^-1)s(^-1) at 20K. Magnetically, the samples generally show a paramagnetic signal that is swamped by the diamagnetic background of the substrate and buffer layers. The paramagnetisrn can be well modelled using a Curie Weiss fit. A number of the samples show a saturation in the magnetisation, which, has been explained via the use of vacancy ordering within MnTe regions in the sample. The susceptibility of the samples has been investigated using a Faraday balance system, and this data has been fitted using; a cluster model for Mn ions within the sample. The photomagnetisation of Cd(_0.9)Mn(_0.1)Te:In has been investigated using a faraday balance system, and modelled using the work of Dietl and Sample, to calculate the number of polarons that had formed on donors in the sample, ΔN(_D)(^MAG) = 1.28x10(^15)cm(^-3). The number of donors in the sample has been measured by means of the Hall effect, ΔN(_D)(^ELEC) = 1.92x10(^15)cm(^-3), and this value compared to that obtained from the model. We have proposed a model to explain this discrepancy based on the concept of band tails in the impurity band.
43
Verdes, Claudiu Georgel. "Models of microstructure and magnetic properties for magnetic recording media." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/3091/.
Full textAbstract:
Three computational models have been developed to simulate magnetic properties of granular media, particulate media microstructures and self-assembled systems. The granular media model uses an energy minimisation approach to describe the magnetic properties of a system of randomly oriented single-domain particles taking into account dipolar and exchange interactions as well as thermal effects. At low temperature dipolar interactions produce flux closure vortex structures leading to a decrease of both remanence and coercivity. When thermal effects become important, dipolar interactions lead to an increase of the local energy barriers increasing both remanence and coercivity as compared to the superparamagnetic case. Exchange coupling tends to align the magnetic moments producing an increase in the remanence of such systems while cooperative reversals decrease their coercivity. The particulate media model uses a spherocylindrical approximation for the elongated magnetic particles that are used in tapes. The particles are allowed to move in a viscous solvent under the action of steric and magnetic interactions and of the orienting field. A percentage of the particles are grouped in clusters that behave as rigid bodies during the simulation. The results obtained suggest that the presence of the clusters leads to a disruption in the alignment of the free particles regardless of the cluster size. A third model uses a Monte-Carlo approach to describe the self-assembly process that occurs in surfactant coated magnetic particles. As the solvent dries the particles form assemblies to minimize the interaction energy. In order to obtain long-range self-assembled systems the particle areal density must be in a narrow range and the particle size distribution must have a standard deviation below 5%. The occurrence of local self-assembly is due to the presence of an attraction term in the interparticle interaction potential. The conditions under which square vs. hexagonal lattice can be obtained are discussed.
44
Lukawska, Anna Beata. "THERMAL PROPERTIES OF MAGNETIC NANOPARTICLES IN EXTERNAL AC MAGNETIC FIELD." Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1401441820.
Full text
45
Feng, Qi. "Magnetic and magneto-optical properties of magnetic oxide thin films." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/3801/.
Full text
46
King, James Gagwane. "Magnetic properties of arrays of magnetite particles produced by the method of electron beam lithography (EBL)." Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/15171.
Full textAbstract:
This study involves the production of arrays of parallelepiped magnetite particles in the size range 0.1 - 1 μm. This was achieved by utilising electron beam lithography techniques which are often employed in the design of semi-conductor devices. These particles are required in order to understand the mechanism of reversal of magnetisation for pseudo-single-domain (PSD) particles important to paleomagnetic studies. The samples used by previous researchers are magnetite powders. In such samples, despite attempts to disperse the particles onto non-magnetic matrix, there is no way of eliminating particle clumping, and magnetostatic interaction. Low temperature magnetic measurements obtained using samples of cubic arrays of magnetite particles shows that the effect of particle clumping is to increase the amount of saturation isothermal remanence (SIRM) lost at the Verwey transition. The dependence of SIRM lost at the Verwey transition on particle size in the PSD size range, is consistent with the vortex domain structure predicted for unconstrained 3-D micromagnetic studies. The results shows that 'true' magnetic memory is a stress related phenomenon. Magnetic properties of cubic arrays of magnetite particles measured at room temperature are not consistent with the mechanism of magnetic reversal of coherent rotation of atomic magnetic moments, but are generally in good agreement with that of vortex nucleation and propagation in general. The method of domain classification using the coercivity ratio often used in rock magnetism, is shown to be not useful in classifying PSD in the submicron size range. Magnetic properties of rectangular parallelepiped magnetite particles are more complex than expected from the simple demagnetisation shape anisotropy contribution.
47
McCoy, James Martin. "The physical properties of magnetic inks." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6646/.
Full textAbstract:
The magnetic particle inspection (MPI) method is a widely used non destructive testing (NDT) technique for ferrous structures. Magnetic inks used in MPI are suspensions of fine ferro/ferrimagnetic particles which, when applied to a magnetized test specimen, delineate surface flaws. This work is an investigation of some of the properties of magnetic ink systems and some aspects of their interaction with defect leakage flux. Reviews of magnetism, the MPI method and leakage flux at defects are given. The construction, characterization and automation of a 1.2 T electromagnet vibrating sample magnetometer, used for magnetic measurements on the inks, is described. The instrument has a resolution of better than l0(^-9) JT(^-1) . A 2D model of indication formation in MPI, based upon the simulation of many particles in the neighbourhood of a defect, is presented. Results of the role of several of the model parameters are given. Results indicate that carrier coefficients of viscosity at the lower end of the range investigated (η = 0.3 mPas) are optimum. The size and contrast of an indication increases with defect size. The contrast and rate of formation of contrast increase with defect aspect ratio. The effect of the contrast paint layer thickness indicates that the recommendation of the British Standard, BS 5044 (1973), is qualitatively correct. Experimental observations of particles in field gradients reveals a discrepancy between theoretical and observed behaviour which is attributed, in particular, to unobservable voids in the particles. Detailed characterization of the particles shows them to be aggregates of 20 - 200 nm crystallites which are probably single domain particles. The morphology of larger aggregates is related to measurements of the low field susceptibility. Evidence from intensive magnetic measurements supports the relationship between magnetic properties and aggregate characteristics. A 'In t' magnetic viscosity effect is reported. At 77 K, the coefficient of magnetic viscosity has a maximum near the coercivity field.
48
Beguivin, Anthony. "Domain wall behaviour in magnetic nanowires." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708692.
Full text
49
Okatan, Mahmut Baris. "Microstructure Development In Nickel Zinc Ferrites." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12606924/index.pdf.
Full textAbstract:
Nickel zinc ferrites (NZF) have been considered as one of the basic components in high frequency electromagnetic applications especially in the field of telecommunications. In the present study, the aim was to produce high quality nickel zinc ferrite ceramics at low soaking temperatures. For this purpose, conventional ceramic manufacturing method based on mixed oxide precursors was followed using calcium fluoride, CaF2, as sintering additive.
During the sintering studies, it was noticed that both the microstructure and the electromagnetic properties of the NZF ceramics were modified to a great extent by CaF2. Therefore, material characterization studies involving microstructural, dielectric and magnetic properties were conducted with respect to CaF2 content of ceramics and soak duration.
The results showed that due to the presence of CaF2 in ceramics, significant improvements were achieved not only in kinetics of sintering but also in the parametersDC electrical resistivity, dielectric constant and dielectric loss factor. For example, 1.0 wt% CaF2 added NZF ceramic produced in this study had a DC electrical resistivity of 1011 &
#61527
-cm which was 100,000 times bigger than the one attained in pure NZF ceramic. On the other hand, the dielectric constant exhibited a flat behavior up to 40 MHz with a value around 16. In addition, no resonance peak was observed in dielectric loss factor spectra, and the typical values of dielectric loss factor lied below 0.01. Besides the achievements mentioned, the magnetic properties such as relative magnetic loss factor and hysteresis parameters were also improved.
50
Wikberg, Magnus. "Fundamental Properties of Functional Magnetic Materials." Doctoral thesis, Uppsala universitet, Teknisk-naturvetenskapliga fakulteten, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-133257.
Full textAbstract:
Magnetic properties of powders, thin films and single crystals have been investigated using magnetometry methods. This thesis provides analysis and conclusions that are supported by the results obtained from spectroscopic and diffraction measurements as well as from theoretical calculations. First, the magnetic behavior of transition metal (TM) doped ZnO with respect to doping, growth conditions and post annealing has been studied. Our findings indicate that the magnetic behavior stems from small clusters or precipitates of the dopant, with ferromagnetic or antiferromagnetic interactions. At the lowest dopant concentrations, the estimated cluster sizes are too small for high resolution imaging. Still, the clusters may be sufficiently large to generate a finite spontaneous magnetization even at room temperature and could easily be misinterpreted as an intrinsic ferromagnetic state of the TM:ZnO compound. Second, influence of lattice strain on both magnetic moment and anisotropy has been investigated for epitaxial MnAs thin films grown on GaAs substrates. The obtained magnetic moments and anisotropy values are higher than for bulk MnAs. The enhanced values are caused by highly strained local areas that have a stronger dependence on the in-plane axis strain than out-of plane axis strain. Finally, spin glass behavior in Li-layered oxides, used for battery applications, and a double perovskite material has been investigated. For both Li(NiCoMn)O2 and (Sr,La)MnWO6, a mixed-valence of one of the transition metal ions creates competing ferromagnetic and antiferromagnetic interactions resulting in a low temperature three-dimensional (3D) spin glass state. Additionally, Li(NiCoMn)O2 with large cationic mixing exhibits a percolating ferrimagnetic spin order in the high temperature region and coexists with a two-dimensional (2D) frustrated spin state in the mid temperature region. This is one of the rare observations where a dimensional crossover from 2D to 3D spin frustration appears in a reentrant material.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 720