Дисертації з теми "Nano-magnetism"
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Cook, James. "Optical magnetism with metallic nano-composites." Thesis, University of Surrey, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616915.
Повний текст джерелаPersson, Andreas. "X-ray Absorption Spectroscopy on Nano-Magnet Arrays and Thin Films : Magnetism and Structure." Doctoral thesis, Uppsala universitet, Yt- och gränsskiktsvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-112824.
Повний текст джерелаMaurer, Thomas. "Magnetism of anisotropic nano-objects : magnetic and neutron studies of Co1-xNix nanowires." Paris 11, 2009. http://www.theses.fr/2009PA112340.
Повний текст джерелаMagnetism of individual nano-objects is a very active research field thanks to the development of original synthesis routes and investigation tools. This thesis aims at probing the magnetism of nanowires synthesized via a pure chemical route, the polyol process. This process provides a large variety and an excellent crystallinity of the synthesized nanowires. This process allows to tune the diameter of the nanowires from 7nm to 20nm leading to coherent magnetization reversaI in the nanowires. I show how the large shape and magnetocrystalline anisotropies provide large coercivities compared to magnetic nanowires synthesized via other routes. Furthermore, the oxidation of such objects has also been investigated. Magnetic measurements has revealed unsual temperature dependencies of both the coercive and exchange fields, emphasizing the role of the superparamagnetic fluctuations of the CoO antiferromagnetic grains in the Exchange Bias effect. Finally, this thesis also aims at developing Polarized Small Angle Neutron Scattering to probe magnetism in complex nano-objects. Such a technique has been ignored until now to study magnetic anisotropic nano-objects despite being well adapted. The key ingredient to carry through such a study is the perfect alignment of the nanowires. This is why, besides the nanowires synthesized via the polyol process, Polarized Small Angle neutron Scattering measurements have been performed on arrays of magnetic nanowires included in porous alumina membranes
Lima, Valquiria Fernanda Gonçalves de. "Preparação e caracterização de nanopartículas magnéticas de Sm-Co, Nd-Fe-B, Fe-Pt e Co-Pt pelo método de agregação gasosa." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26112014-135553/.
Повний текст джерелаIn the recent years, nanoparticles (NPs) are being in all fields of technology. Their promising applications involve among others, the field of sensors and transducers, magnetic recording media, magnetic carriers of medicinal drugs. Aiming to produce NPs by physical method, a generator of nanoparticles was adapted using a system of guns \"magnetron sputtering\", based on the aggregation gas method. With the generator we are able to produce NPs with different types of material. In this work, we present the development of the methodology for the production of nanoparticles of hard magnetic materials, using targets of SmCo5, Sm2Co17, Nd2Fe17B, FePt and CoPt. We investigated the influence of the deposition parameters (pressure, gas flux and sputtering power), substrate type and the existence of the buffer and/or codeposition layers, to obtain the desired structural and magnetic properties for the nanoparticles. The produced NPs were magnetically analyzed by VSM and SQUID, the morphology and size by TEM and SEM, the stoichiometry by RBS and the crystal structure by XRD. The main objective of this work is to obtain nano-magnet with high magnetic anisotropy. Through the morphological characterization by electron microscopy, we found for NPs produced and studied have diameters between 5 and 17 nm. Through RBS analysis we have obtained the composition of the NPs, and also that they have different stoichiometry in relation to the used targets. Structural and magnetic studies have show that for Sm-Co, Fe-Pt and Co-Pt it is possible to obtain crystalline NPs with coercive field around 1 kOe.
Lifvenborg, Louise. "Fabrication and characterization of novel nano-magnets." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-420995.
Повний текст джерелаOpponent: Stivan Sabir
Delshadi, Sarah. "Tests de diagnostic immunologique rapides combinant des nanoparticules magnétiques et des micro-aimants structurés." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAV070.
Повний текст джерелаThis thesis reports the development of innovative, sensitive and fast immunoassays combining functionalized superparamagnetic nanoparticles (SPN) and micro-magnets. Our magnetic immunoassays exploit high gradients generated by micro-magnets to capture immune-complexes captured on SPN. Magnetic attraction is widely used in biotechnology, because it provides long-range forces able to capture molecules of interest. Bead-based immunoassays use common centimetre-scale magnets to attract micro-particles. Those magnets generate low magnetic gradients and struggle to capture superparamagnetic nano-particles, which are too small and mobile to be efficiently trapped. Down-scaling the size of magnetic particles is very interesting since it allows diffusion-based transport to perform faster reactions, while avoiding particle sedimentation and aggregation. Furthermore, it increases the reaction surface, which improves the sensitivity of immunoassays. Thanks to the scaling law effects micro-magnets from Institut Néel generate high local gradients and therefore large magnetic volume forces: we use this innovative technology to develop fast immuno-assays that take advantage of a radical size reduction, compared to commercial technology.We first developed a colorimetric magnetic immunoassay (MagIA) as a new approach to standard ELISA. A proof-of-concept based on colorimetric quantification of anti-ovalbumin antibody in buffer was performed and compared with conventional ELISAs. After optimization, MagIA exhibits a limit of detection and dynamic range similar to ELISAs developed using the same biochemical tools. Micromagnets made by the micro-magnetic imprinting method can be fully integrated in multi-well plates at low cost, allowing the efficient capture of immuno-complexes carried by SPNs. The method is generic and performs magnetic ELISA in 30 min.We then developed a magnetically localized fluorescent immunoassay (MLFIA) exploiting the local capture of SPN on micro-magnets. The differential measurement of fluorescence localized on and besides micro-magnet arrays allows the detection and quantification of a molecule in only 15 minutes without fluid handling. We present a proof of concept based on the detection of monoclonal antibody anti-ovalbumin. Functionalized nanoparticles are incubated with fluorescent detection antibody and the sample containing the molecule to be detected. After a single incubation step, the nanoparticles are captured on micro-magnets made by thermo-magnetic patterning. Fluorescence is then read under a microscope. Differential measurement between the signal from the immunological complex localised on the micro-magnets and the non-specific signal localised besides micro-magnets allows the quantification of mAb anti-OVA. The performance of MLFIA was compared with conventional ELISA and exhibits a limit of detection up to 100 times better for anti-OVA mAb in PBS. For further validation, MLFIA was used to measure clinical parameters: we developed a sandwich assay to detect C-reactive protein, and a serology for Toxoplasma gondii immunoglobulin G and M or osteopontin in human samples. Comparisons with data obtained with routine clinical automatized methods show excellent correlation. Our MLFIA technology presents several key advantages: it is compatible with biological media (serum, plasma), uses small volumes and requires little energy. It also is versatile and thus can be used to detect any antigen or antibody in complex media. We are currently developing a portable prototype for point-of-care diagnostics. The results will open the way to a new generation of sensitive immunological lab-on-chip
Panighel, Mirco. "Adsorption, metalation and magnetic properties of tetra phenyl porphyrins on metal surfaces." Doctoral thesis, Università degli studi di Trieste, 2015. http://hdl.handle.net/10077/10898.
Повний текст джерелаTraditional semiconductor technology will reach a size limit within the next few years. A possible solution could be the use of organic molecules in technological applications as single functional units in metal-organic based devices; the success of this approach strongly depends on the understanding of the behaviour of these molecules on metallic surfaces. The interaction with metallic substrates and the interaction between the molecules themselves determine the electronic and magnetic properties of the system, and it is thus of fundamental interest to study these metal-organic interfaces both in the case of single molecules and layer structures. In this thesis, an extensive study of the electronic and magnetic properties of tetra-phenyl-porphyrin (2H-TPP) molecules adsorbed on metal surfaces is reported. By means of scanning tunnelling microscopy (STM) we studied the adsorption geometry of these molecules on the Au(111), Ag(111) and Cu(100) surfaces. By using X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, a temperature-induced conformational adaptation reaction of the 2H-TPP molecules adsorbed on the Au(111) and Ag(111) surfaces, upon annealing at 550 K, is described. A possible dehydrogenation reaction, with the formation of new C-C bonds, could explain the rotation of the molecule phenyl rings parallel to the surface plane and the associated increasing in the molecule-substrate interaction. In-situ metalation of porphyrins in ultra-high vacuum is obtained by two methods: in the first one, the metalation of 2H-TPP on Ag(111) is achieved by direct metal evaporation (Mn, Rh and Fe) on the molecular layer; in the second case we report the self-metalation of 2H-TPP through the coordination with a metal atom from the Fe(110) and Al(111) substrates. In addition, we investigated the effects of metalation and temperature-induced conformational adaptation on the molecule-substrate interaction, by means of XPS and NEXAFS, in the case of CoTPP on Ag(111). The magnetic properties resulting from the metal coordination are studied by X-ray magnetic circular dichroism (XMCD). Here, a description of the magnetic coupling of a MnTPPCl single layer with a Fe(110) ferromagnetic substrate is disclosed. Moreover, we focused on the study of the magnetic properties and exchange coupling of two layer of molecule and a ferromagnetic thin film. In the case of a MnTPP layer on FeTPP/Fe(110) the magnetic coupling extends to the second layer of molecules, for which the magnetization is opposite with respect to the substrate.
Le tradizionali tecnologie utilizzate nell’industria dei semiconduttori raggiungeranno, entro breve tempo, il limite nella miniaturizzazione dei loro componenti. Una possibile alternativa potrebbe venire dall’utilizzo di molecole organiche come singole unità funzionali in dispositivi metallo-organici; d’altra parte il successo di questo approccio dipende in maniera sostanziale dalla comprensione del comportamento di queste molecole sulle superfici dei metalli. L’interazione con il substrato metallico e la stessa interazione tra le molecole determinano le proprietà elettroniche e magnetiche di questi sistemi, ed è dunque di fondamentale interesse lo studio di queste interfacce metallo-organiche sia nel caso di singole molecole che di strutture più complesse. In questa tesi è riportato uno studio dettagliato delle proprietà elettroniche e magnetiche di tetra-fenil-porfirine (2H-TPP) adsorbite su superfici metalliche. Attraverso la microscopia a scansione a effetto tunnel (STM) è stata studiata la geometria di adsorbimento di queste molecole sulle superfici Au(111), Ag(111) e Cu(100). Utilizzando le spettroscopie XPS (X-ray photoemission spectroscopy) e NEXAFS (near-edge X-ray absorption fine structure) è descritta la reazione di adattamento conformazionale delle 2H-TPP adsorbite sulle superfici Au(111) e Ag(111) a seguito del processo di annealing a 550 K. Una possibile reazione di de-idrogenazione, con la formazione di nuovi legami C-C, può spiegare la rotazione dei gruppi fenili della molecola verso la superficie e l’aumento dell’interazione molecola-substrato ad esso associato. La metallazione in-situ delle porfirine in ultra-alto vuoto è ottenuta in due modi: nel primo, la metallazione delle 2H-TPP su Ag(111) è raggiunta con la diretta evaporazione del metallo (Mn, Rh e Fe) sullo strato di molecole; nel secondo caso, sulle superfici Fe(110) e Al(111) la metallazione avviene automaticamente tramite la coordinazione della 2H-TPP con un atomo della superficie. Inoltre, gli effetti della metallazione e dell’adattamento conformazionale sull’interazione molecola-substrato sono stati studiati, tramite XPS e NEXAFS, nel caso di CoTPP su Ag(111). Le proprietà magnetiche risultanti dalla coordinazione della molecola con un atomo metallico sono state studiate per mezzo della tecnica XMCD (X-ray magnetic circular dichroism). In particolare, viene descritto l’accoppiamento magnetico di un singolo strato di MnTPPCl con un substrato ferromagnetico Fe(110). Inoltre, ci si è focalizzati sullo studio delle proprietà magnetiche tra due strati di molecole e un film sottile ferromagnetico. Nel caso specifico di MnTPP su FeTPP/Fe(110) l’accoppiamento magnetico si estende al secondo strato di molecole, per il quale la magnetizzazione è opposta rispetto al substrato.
XXVII Ciclo
1986
Bonetti, Stefano. "Magnetization Dynamics in Nano-Contact Spin Torque Oscillators : Solitonic bullets and propagating spin waves." Doctoral thesis, KTH, Materialfysik, MF, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26955.
Повний текст джерелаQC 20101130
Sá, Artur Domingues Tavares de 1985. "Nano-agregados metálicos = produção e propriedades magnéticas." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276993.
Повний текст джерелаTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-23T00:51:37Z (GMT). No. of bitstreams: 1 Sa_ArturDominguesTavaresde_D.pdf: 7427611 bytes, checksum: 5f7375c13b84237cc30bec5c926f2f65 (MD5) Previous issue date: 2013
Resumo: Clusters, i.e. nanopartículas formadas por alguns átomos ou até 107, atraem grande interesse devido 'as propriedades peculiares que apresentam, como momento magnético aumentado, atividade catalítica, fluorescência dependente de tamanho e estruturas geométricas diferenciadas em relação ao material massivo. Isso acontece principalmente devido aos efeitos decorrentes da grande razão entre o número de átomos na superfície e o número de átomos no volume, e também por conta dos níveis discretos de energia devidos ao pequeno número de átomos presente nas estruturas. Entretanto, para que seja possível uma melhor compreensão dos mecanismos envolvidos em amostras compostas por clusters, 'e imprescindível que tenhamos um grande controle dos parâmetros cruciais como tamanho das partículas, concentração e energia de deposição. Para isso, desenvolvemos e construímos uma fonte para a produção de agregados com um número controlável de átomos, com a intenção de produzir partículas com 2 até 100 átomos. Um feixe de partículas 'e produzido, caracterizado e depositado em condições de ultra alto vácuo (UHV), utilizando-se uma fonte de clusters com magnéton sputtering. A fonte 'e baseada na proposta por Haberland et al. (1) com a inovadora introdução de um sputtering com geometria cilíndrica, com a intenção de aumentar a eficiência na criação de partículas bem como facilitar a produção de agregados de ligas. Uma fonte de clusters geralmente é constituída essencialmente de: uma fonte de átomos e uma câmara de agregação, para gerar as partículas; um sistema de lentes eletrostáticas, para guiar e focalizar o feixe; e um analisador de massa, podendo esse selecionar, ou não, as partículas em massa. Para fonte de átomos desenvolvemos dois magnéton sputterings, um magnéton circular plano típico de 1" e um magnéton cilíndrico para a erosão axial de fios metálicos. A câmara de agregação tem um comprimento variável (0-300 mm), para que possamos controlar o tamanho médio dos nano-agregados. Um skimmer, três lentes Einzel e uma Bessel-Box são utilizadas para guiar e focalizar o feixe de partículas ao longo do instrumento. Como analisador de massa, construímos um espectrômetro de massa por tempo de voo. É importante frisar que optamos por desenvolver a maioria dos componentes na própria Unicamp, estes componentes serão descritos no corpo dessa tese. O equipamento que se encontra operacional, já se mostrou capaz de produzir partículas com mais de 500 átomos, superando assim nossas expectativas iniciais. Apresentamos também a caracterização magnética de nanoestruturas granulares com nano-agregados de cobalto com 2,3 nm de diâmetro embebidos em matrizes de cobre com diferentes concentrações. A comparação dos resultados utilizando-se o triple fit e medidas de transporte mostra que apenas para baixa concentração (0,5 at.% Co) todos os experimentos são consistentes com a suposição de que as partículas são não-interagentes e a descrição teórica comumente utilizada é apropriada. Aumentando-se a concentração para 2,5 at.% e 5 at.% implica em desvios entre magnetometria e magneto-transporte
Abstract: Clusters, i.e. nano-particles formed by a few tens or up to 107 atoms, attract great interest due to their peculiar properties as enhanced magnetic moment and catalytic activity, size-specific fluorescence and non-bulky geometrical structures. This happens mainly due to effects arising from their high surface-to-bulk ratio and because of the discrete energy levels due to the small amount of atoms at these structures. However, in order to get a deeper understanding of the mechanisms taking place in cluster-assembled samples, it is fundamental to have a good control of crucial parameters such as clusters size, composition, concentration and deposition energy. In this way, we have developed and constructed a source to produce clusters with a controllable number of atoms intended to produce particles ranging from 2 up to 100 atoms. A beam of cluster ions is produced, characterized and deposited under ultra high vacuum (UHV) conditions, using a magnetron sputtering cluster source. This source is based on the design of Haberland et al. (1) with the innovative introduction of a cylindrical sputtering geometry that intends to increase the particle generation efficiency also to facilitate the production of alloy clusters. A usual clusters source is constituted essentially of an atom source and aggregation chamber, to generate the particles; electrostatic lenses, to guide them; and a mass analyzer, which may, or not, select the particles by mass. For the atom source we have designed two sputtering-like sources, a home-made 1" typical planar magnetron and also a home-made cylindrical one, for axial erosion of wire targets. The aggregation chamber has a variable length ( 0-300 mm), so we can control the average size of the clusters. A skimmer, three Einzel lenses and a Bessel-Box are used to guide charged cluster through the instrument. As mass analyzer we have built Time-Of-Flight mass spectrometer. It is important to say that we choose to build almost all the components at Unicamp, these components will be described in the body of this thesis. The equipment, which is operational, showed itself capable to produce particles with more than 500 atoms, exceeding our initial expectations. We also report on magnetic characterization of clusterassembled nanostructures with cobalt clusters with 2.3 nm diameter embedded in copper matrices at different concentrations. Results from the triple fit and transport measurements were compared and showed that only at low concentration (0.5 at % Co) all experiments are consistent with the non-interacting particles assumption and the common theoretical description is appropriate. Increasing the concentration to 2.5 at.% and 5 at.% implies deviations between magnetometry and magnetotransport
Doutorado
Física
Doutor em Ciências
Vergnaud, Céline. "Optimisation de la croissance de MoSe2 - WSe2 par épitaxie de Van der Waals pour la valleytronique." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY038.
Повний текст джерелаThe purpose of this thesis is to optimize growth by molecular beam epitaxy in the van der Waals regime of two-dimensional (2D) semiconductor layers of transition metal diselenides (MoSe2, WSe2) for magneto-optical and electric studies. This optimization involves improving the crystallographic quality of the layers over large areas by adjusting the growth parameters (temperature and flux). In particular, the control of the surface state of the substrate is decisive on the growth mechanisms of these layers. The development of these low-dimensional materials required the use of advanced characterization techniques (Grazing incidence X-ray diffraction, High Resolved Transmission Electronic Microscopy, ect). In this thesis, we focused on two specific substrates : silicon oxide and mica. They both have the particularity of being insulating and inert from an electronic point of view, which is essential to probe the optical and electrical intrinsic properties of 2D layers. Finally, we developed electrical doping (p doping) for microelectronics and magnetic (Mn doping) for valleytronics
Burgos, Parra Erick Omar. "Time resolved and time average imaging of magnetic nano-structures." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34251.
Повний текст джерелаAlqannas, Haifa Saleh. "The Jahn Teller and surface interactions in C₆₀ nano systems." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14609/.
Повний текст джерелаHamadeh, Abbass. "Synchronization of spin trasnsfer nano-oscillators." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112262/document.
Повний текст джерелаSpin transfer nano-Oscillators (STNOs) are nanoscale devices capable of generating high frequency microwave signals through spin momentum transfer. Although they offer decisive advantages compared to existing technology (spectral agility, integrability, etc.), their emitted power and spectral purity are quite poor. In view of their applications, a promising strategy to improve the coherence and increase the emitted microwave power of these devices is to mutually synchronize several of them. A first step is to understand the synchronization of a single STNO to an external source. For this, we have studied a circular nanopillar of diameter 200~nm patterned from a Cu60|Py15|Cu10|Py4|Au25 stack, where thicknesses are in nm. In the saturated state (bias magnetic field > 0.8 T), we have identified the auto-Oscillating mode and its coupling to an external source by using a magnetic resonance force microscope (MRFM). Only the uniform microwave field applied perpendicularly to the bias field is efficient to synchronize the STNO because it shares the spatial symmetry of the auto-Oscillation mode, in contrast to the microwave current passing through the device. The same sample was then studied under low perpendicular magnetic field, with the two magnetic layers in the vortex state. In this case, it is possible to excite a highly coherent mode (F/∆F>15000) with a linewidth below 100 kHz. By analyzing the harmonic content of the spectrum, we have determined that the non-Linear amplitude-Phase coupling of the excited mode is almost vanishing, which explains the high spectral purity observed. Moreover, the oscillation frequency can still be widely tuned thanks to the Oersted field created by the dc current. We have also shown that the synchronization of this mode to a microwave field source is very robust, the generation linewidth decreasing by more than five orders of magnitude compared to the autonomous regime. From these findings we conclude that the magneto-Dipolar interaction is promising to achieve mutual coupling of vortex based STNOs, the dipolar field from a neighboring oscillator playing the role of the microwave source. We have thus experimentally measured a system composed of two STNOs laterally separated by 100 nm. By varying the different configurations of vortex polarities, we have observed the mutual synchronization of these two oscillators
Menshawy, Samh. "Réponse dynamique d’un nano-oscillateur spintronique à un signal rf pour le développement de nouveaux détecteurs rf ultra-miniatures." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS076/document.
Повний текст джерелаSpintronic nano-oscillators have remarkable properties in terms of radio frequency detection. Their nanoscale sizes, room temperature operation, and CMOS compatibility make them serious candidates for providing instantaneous spectral analysis in embedded systems. This thesis concerns the detection properties of magnetic vortex-based STNOs. One of the effects conferring on STNOs the possibility of detecting a rf signal is the spin diode effect. An rf source is used to create the signal to be detected. When the rf current frequency injected into the STNO corresponds to its resonant frequency, a rectification voltage is created at its terminals. The measurement of this voltage by a simple voltmeter makes possible to determine the rf current presence. The evolution study of the resonance frequency as a function of the STNO radius, the dc current and the magnetic field has highlighted the possibility of choosing the resonant frequency and tuning it with these parameters. From an application point of view, this property is essential for allocating an STNO to a specific frequency to be detected. Furthermore, the STNO nanometric allows us to envisage a network of thousands, even millions of STNOs contained on a chip operating at ambient temperature. However, several problems arise. The STNO sensitivity to an external rf signal must allow to determine the occupancy state of a frequency channel by a simple measurement of the voltage or with a voltage comparator. This requires a voltage variation of ten mV order. The spin diode effect doesn’t allow to achieve such variation. Another effect, measured for the first time at the Unité Mixte de Physique CNRS/Thales, called magnetic vortex expulsion, is studied. This phenomenon occurs when the vortex core crosses the STNO edges during its spin transfer induced dynamics. Thanks to this effect, the voltage amplitude variation can reach up to 25 mV in the STNOs characterized during this thesis. Moreover, this phenomenon can be tuned. From an application perspective, a network of STNOs must be created in order to allocate an STNO to a specific frequency range and thus cover a broad frequency band.The rf current distribution to all STNOs is therefore a problem to which we have brought a solution. The excitation of the vortex core by a rf field allows us to excite a large number of STNO thanks to an inductive line lithographed above the STNOs. The possibility of expelling the vortex core under these conditions has been demonstrated. We then studied the vortex core dynamics induced by an rf field during the expulsion. A time and frequency domain studies not only provided us detection time information of an rf signal by the STNO but also on its magnetization in the expulsion regime. Moreover, the STNO frequency tuning is possible even when the vortex core is excited by an rf field. Finally, these studies enabled us to implement step by step a proof of concept demonstrating the rf detection feasibility with spintronic nano-oscillators. The various studies of vortex core expulsion combined with a considerable technical work of design and manufacture finally allowed us to converge towards a solution that constitutes a starting point towards the development of a broadband spintronic spectrum occupancy detector, contained on a chip and operating at room temperature
Benchohra, Amina. "Magnetic molecular switches : from their synthesis to their integration into hybrid (nano)materials." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS489.
Повний текст джерелаMolecular switchesare molecules that can asdjust their(chemical, physical) properties in response to an external stimulus. The fascinating properties of molecular switches have drawn most attention in molecular electronics and more generally in advances materials research. This PhD project was developped at the frontiers of ERMMES and Polymeres research themes, in the framework of a first collaboration. Our major interest was to establish reliable synthetic routes for the design of hybrid (nano)materials based on magnetic molecular switches. The work was particularly focused on spin crossover complexes and a family of photomagnetic cyanide-bridged Fe/Co cages. These switches were first functionalized at their periphery, on the tris(pyrazolyl)borate capping ligand used for their synthesis. The functionalization influence on the switches properties were carried out to target the best candidates for hybrid materials design. Then, we dedicated efforts on the intergration of magnetic molecular switches into two main classes of materials, (i) surfaces and (ii) organic polymers, through wet-chemistry approaches. This manuscript combines this set of studies
Zakhia, Georges. "Synthèse, caractérisation et propriétés magnétiques de nano-aimants moléculaires." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112071.
Повний текст джерелаIn the first part of this thesis, we studied the magnetic anisotropy of pentacoordinated mononuclear Ni(II) and Co(II) complexes possessing geometries from square pyramid to trigonal bipyramid. We have shown that, for a given geometry, the metal ion nature has an important influence on the magnetic anisotropy.Then, we studied for a given metal ion the effect of geometry on its magnetic anisotropy. In the case of a trigonal bipyramidal geometry (C3v symmetry), we showed that Co(II) has an Ising type anisotropy (easy axis of magnetization) and thus a blocking of magnetization that leads to an opening of a hysteresis cycle at low temperature. This type of complexes can be used for storing data albeit at low temperature.In the second part of the work, we studied the magnetic properties of binuclear complexes. A binuclear Co(II) complex bridged by two Cl- has a weak ferromagnetic coupling and a blocking of its magnetization.Finally, another aspect of this work was to design binuclear complexes, where two anisotropic ions having each one an easy axis of magnetization, are weakly antiferromagnetically coupled. To do this, we have studied compounds with cryptand ligands where the geometry around the Co (II) is trigonal bipyramid. We found that with a Cl- or Br- bridging ligand, the exchange interaction is much more important than the local anisotropy of Co(II) ions leading to a magnetic behavior where the ions lose their local character. This work opens up prospects for synthesizing the same type of complex but with larger bridges to decrease the intensity of the antiferromagnetic coupling
Mirza, Mueed. "Magnetism in Ni80Fe20 and Ni80Fe20/NiO Nano-stripes." 2012. http://hdl.handle.net/1993/8454.
Повний текст джерелаJia-FangZhang and 張嘉芳. "Study on synthesis and magnetism of nano-hematite, nano-magnetite and nano-maghemite with different crystal morphologies." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/85525405426568850014.
Повний текст джерела國立成功大學
地球科學系
102
The objective of this study is to investigate the magnetic properties of nano-hematite, nano-magnetite, and nano-maghemite with morphologies of nano-particle, nano-rod, nano-tube, and nano-ring. Four crystal morphologies of nano-hematite are synthesized by a hydrothermal method. Nano-magnetite is prepared via nano-hematite by using carbon reduction method. Nano-maghemite is obtained by oxidation of nano-magnetite. The particle-shaped nano-hematite has a granular morphology with aparticle size of 45~85 nm; the nano-rod is 50~100 nm in width and 250~350 nm in length; nano-tube has a inner-diameter of 40~85 nm width and 150~300 nm length; nano-ring shows a inner-diameter of 20~45 nm and outer-diameter of 70~100 nm. The particle size and morphology of nano-magnetite and nano-maghemite are almost the same as nano-hematite. It exhibits that all nano-hematites have a weak ferro-magnetism with multi-domains, however, all nano-magnetites and nano-maghemites are ferri-magnetic with pseudo-single-domain measured by superconducting quantum interference device magnetometer. The spatial distribution of magnetism are characterized by magnetic force microscopy (MFM). The MFM phase images show bright and dark areas, implying ferro-magnetic domains for nano-magnetite and nano-maghemite. Moreover, it reveals a complicated magnetic arrangement for nano-magnetite and nano-maghemite with crystal shapes of rod, tube and ring. Nano-magnetite and nano-maghemite with particle-shape both have a single-domain. This suggests the crystal structure and morphology have an impact on magnetic properties. The MFM technique could be applied in the explaination of paleomagnetism and environmental implications of fault zones.
CHANG, CHEN LUN, and 張禎倫. "Preparation and charactenzation of magnetism nano particles with photo catalytic activity." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/92788377830809239181.
Повний текст джерела萬能科技大學
材料科學與工程研究所
101
There are two works in our research. The first one is prepare Fe3O4 Nanoparticles with superparamagnetism by using precipitation method. The effects on the characteristics of NPs by changing prepared parameters are investigated. The second one is utilize sol gel method to prepare various Fe3O4-SiO2-TiO2 Nanoparticles (F.S.T. NPs). The F.S.T. NPs were encapsulated with high stability SiO2 and photo catalyst TiO2 respectively. The effects on the characteristics of F.S.T. NPs by changing prepared parameters are also investigated. The morphologies, sizes, constructions and magnetisms of NPs and F.S.T. NPs were determined with Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), Energy Dispersive Microscopy (EDS), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Superconducting Quantum Interference Device (SQUID) respectively. The results of experiments described as following: The Fe3O4 NPs all display superparamagnetism in this task. They have the smallest particle size when prepared parameter is pH 12, 85 ℃ and 700 rpm. Its range of particle size located at 6~8nm. The Fe3O4 NPs used as the core material, to form the F.S NPs with core-shell construction via adding appropriate amount of deionized water, ethanol, catalyst and precursor. Then TiO2 encapsulates on the surface of F.S NPs. The F.S.T. NPs possess superparamagnetism and photo catalyst are prepared successfully.
Chen, Yung-Sheng, and 陳永昇. "Microstructure and Magnetism Properties of Nano-sized Iron Oxide Contented Glass Ceramics." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/29123835623622470939.
Повний текст джерела義守大學
材料科學與工程學系
92
The effect of iron oxide(Fe2O3)adding into the glass-ceramics, Li2O-Fe2O3-MnO2-CaO-P2O5-SiO2(LFMCPS), on the crystalline phase transition, microstructures, the grain size of iron oxide phases, and magnetic properties were systematically studied in this thesis. The exothermic peak in DTA measurements for the bulk sample, is about 100℃ different from that for the powder sample illustrates that a surface nucleation process is undertaken in the LFMCPS glass ceramics system. In parallel, the X-ray diffraction pattern proves that the exothermic peak can be resulted form the formation of lithium silicate. After the heat treatment at 850℃ for 4 hours, crystalline phases of LiMn2O4, β-wollastonite(β-CaSiO3), lithium silicate(Li2SiO3), Ca(Mn, Ca)Si2O6, and Li2Ca4Si4O13 were found in all LFMCPS glass-ceramics specimen. However, the (Li, Mn)Ferrite phase was found in the 4wt% Fe2O3 LFMCPS and the Li2FeMn3O8 phase was formed addition to the (Li, Mn)Ferrite as the content of Fe2O3 increased to 8wt%. The microstructure studied by TEM indicates that the (Li, Mn)Ferrite particles dispersed in the matrix of the β-wollastonite. The grain size of (Li, Mn)Ferrite particles smaller than 100nm with an average size of 40nm is found in the 4wt% Fe2O3 LFMCPS glass-ceramics, but the grain size distribution of the (Li, Mn)Ferrite becomes wider ranging from 1μm to 5nm. as the content of Fe2O3 increased to 8 wt%. Based on the experimental results from SQUID and ESR spectrum, the LFMCPS glass-ceramic with 4wt% Fe2O3 exhibits mixed superparamagnetic and ferromagnetic behaviors, but the glass-ceramic with 8 wt %Fe2O3 exhibits ferromagnetic behavior. The superparamagnetic behavior can be attributed to those (Li, Mn)Ferrite with grain size smaller than 40nm, but the ferromagnetic behavior can be attributed to those (Li, Mn)Ferrite of larger grain size.
Weng, Yung-Jin, and 翁永進. "Development of Magnetism-assisted Micro-Imprinting Process for Replication of Nano/Micro-Structures." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/86095087077073228218.
Повний текст джерела國立臺灣大學
機械工程學研究所
97
Micro-nano structural components are the key components to be applied in future instrumentation for digital optoelectronics, telecommunications, flat panel displays, and bio-medicine. The conventional micro-component production technology requires a rigid mold of complicated manufacturing processes, expensive precision equipment, high temperature, and high pressure cooling processes. Therefore, the process has disadvantages, such as time-consuming, costly, and limited in visualization and controllability. This study aimed to develop a micro-nano structural imprinting processing technology of low temperature, low pressure, and rapid prototyping magnetic soft mold. It first integrated the micro-electro-mechanical process, laser processing/gas micro-thermo imprinting micro-structural manufacturing process, Anodic Aluminum Oxide (AAO) method, and nano oxidation technology to produce micro-nano structural patterns. Then, it employed PDMS composite magnetic materials to create a micro-nano structural magnetic soft mold of appropriate structural strength and flexibility by casting mold, and then prepared polymer materials. In the initial stage, it discussed the imprint forming of micro structural reproduction, using gas-assisted powder imprinting micro-forming technology. Then, it employed self-developed magnetic-assisted imprinting processing technology (including electromagnetic controllable imprinting process and electromagnetic UV imprinting process) to discuss the production and detection of magnetic-assisted imprinting processes for micro-nano structural components. Finally, it developed a magnetic roller imprinting process equipment, and successfully produced magnetic rollers, while analyzing and exploring key manufacturing technologies. The main research contents included discussion on micro-nano structural mold processing technology and its applications, analysis and exploration on gas-assisted powder imprinting micro-forming technology, discussion on magnetic-assisted micro-nano structural imprinting process, discussion on micro-nano component detection analysis and development of related processing procedures, and discussion and development of magnetic-assisted roller micro imprinting processing equipment. This study successfully established the integrated technological platform of micro-electro-mechanical processing procedures, laser processing/gas micro-thermo imprinting of micro structure processing procedures, AAO method, nanooxidation processing procedures to prepare micro-nano structural molds supplemented with PDMS composite magnetic material casting imprinting film, and micro nano magnetic soft mold imprinting reproduction, according to magnetic-assisted imprinting processing procedure/magnetic roller imprinting processing procedure. This method is innovative and creative in terms of processing procedures, and has advantages of simple, fast, inexpensive, and available for mass production, as well as providing a better alternative in the reproduction of micro structural components, contributing to the upgrading of the science, and technological industry of micro nano systems.
Yi-PingYu and 尤奕馮. "Effects of raw materials on synthesis and magnetism of iron oxide nano-minerals." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/74905073993279529984.
Повний текст джерелаChiou, Yen-Lin, and 邱彥霖. "Influence of oxygen on the interfacial magnetism of nano-scale Co/Ge (111) ultrathin films." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/31190376607612670298.
Повний текст джерела東海大學
物理學系
93
The main purpose of this research is to study the influences of oxygen exposure on the magnetic properties of Co/Ge(111) ultrathin films in the ultra high vacuum (UHV), and this topic has been attacked using surface magneto-optic Kerr effect (SMOKE) technique for magnetic measurement and Auger electron spectroscopy (AES) for compositional analysis. No magnetic hysteresis loop on the polar configuration is found for Co/Ge(111) films with oxygen exposure. On the longitudinal configuration, the coercivity enhances drastically, but the remanence Kerr intensity reduces slightly with increasing the oxygen exposure time. Besides, no exchange bias phenomenon is observed for Co/Ge(111) films with oxygen exposure after cooling in the magnetic field of 400 Oe to 125 K. From Auger electron spectroscopy, it is found that no oxygen adsorption occurs on either Ge(111) surface or CoGe compound interfaces in ultra high vacuum environment. As the thickness of Co films increases above 6 monolayers, pure cobalt islands form on the surface and the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. From the depth profiling measurements, it is shown that oxygen always distributes on the topmost layers of the film, suggesting that oxygen plays a role as a surfactant. The adsorbed oxygen influences the electronic density of states of Co and leads to the changes of the magnetic properties. The appearance of the O/Co/Ge interface could modify the stress anisotropy, resulting in an increase of the coercivity of ultrathin Co/Ge(111) film.