Дисертації з теми "Magnetic properties of material"
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1
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.
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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.
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3
Björkman, Torbjörn. "Magnetic and Structural Properties of f-electron Systems from First Principles Theory." Uppsala : Acta Universitatis Upsaliensis, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-109639.
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Sandy, I. M. "Solvent induced transitions and magnetic properties of 1-D conductors." Thesis, Cranfield University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233338.
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5
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.
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Rata, Doru Gabriel. "Investigation of material properties by NMR in low and high magnetic fields." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981069592.
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Petrov, Andrii. "Brain Magnetic Resonance Elastography based on Rayleigh damping material model." Thesis, University of Canterbury. Mechanical Engineering, 2013. http://hdl.handle.net/10092/7901.
Повний текст джерелаАнотація:
Magnetic Resonance Elastography (MRE) is an emerging medical imaging modality that allows quantification of the mechanical properties of biological tissues in vivo. MRE typically involves time-harmonic tissue excitation followed by the displacement
measurements within the tissue obtained by phase-contrast Magnetic Resonance Imaging (MRI) techniques. MRE is believed to have great potential in the detection of wide variety of pathologies, diseases and cancer formations, especially tumors.
This thesis concentrates on a thorough assessment and full rheological evaluation of the Rayleigh damping (RD) material model applied to MRE. The feasibility of the RD model to accurately reconstruct viscoelastic and damping properties was
assessed. The goal is to obtain accurate quantitative estimates of the mechanical properties for the in vivo healthy brain via the subzone optimization based nonlinear image reconstruction algorithm.
The RD model allows reconstruction of not only stiffness distribution of the tissue, but also energy attenuation mechanisms proportionally related to both elastic and inertial effects. The latter allows calculation of the concomitant damping properties of the material. The initial hypothesis behind this research is that accurate reconstruction of the Rayleigh damping parameters may bring additional diagnostic potential with regards to differentiation of various tissue types and more accurate characterisation of certain pathological diseases based on different energy absorbing mechanisms. Therefore, the RD model offers reconstruction of three additional material properties that might be of clinical diagnostic merit and can enhance characterisation of cancer tumors within the brain.
A pneumatic-based actuator was specifically developed for in vivo human brain MRE experiments. Performance of the actuator was investigated and the results showed that the actuator produces average displacement in the range of 300 µmicrons and is well suited for generation of shear waves if applied to the human head. Unique features of the the actuator are patient comfort and safety, MRI compatibility, flexible design and good displacement characteristics.
In this research, a 3D finite element (FE) subzone-based non-linear reconstruction algorithm using the RD material model has been applied and rigorously assessed to investigate the performance of elastographic based reconstruction to accurately recover mechanical properties and a concomitant damping behaviour of the material. A number of experiments were performed on a variety of homogenous and heterogeneous tissue-simulating damping phantoms comprising a set of materials that mimic range of mechanical properties expected in the brain. The result showed consistent effect of a poor reconstruction accuracy of the RD parameters which suggested the nonidentifiable nature of the RD model.
A structural model identifiability analysis further supported the nonidentifiabilty of the RD parameters at a single frequency. Therefore, two approaches were developed to overcome the fundamental identifiability issue. The first one involved application of multiple frequencies over a broad range. The second one was based on parametrisation techniques, where one of the damping parameters was globally defined throughout the reconstruction domain allowing reconstruction of the two remaining parameters.
Based on the findings of this research, multi-frequency (MF) elastography was performed on the tissue-simulating phantoms to investigate improvement of the elastographic reconstruction accuracy. Dispersion characteristics of the materials as well as RD changes across different frequencies in various materials were also studied. Simultaneous multi-frequency inversion was undertaken where two models were evaluated: a zero-order model and a power-law model. Furthermore, parametric-based RD reconstruction was carried out to evaluate enhancement of accurate identification of the reconstructed parameters. The results showed that parametric-based RD reconstruction, compared to MF-based RD results, allowed better material characterisation on the reconstructed shear modulus image. Also, significant improvement in material differentiation on the remaining damping parameter image was also observed if the fixed damping parameter was adjusted appropriately.
In application to in vivo brain imaging, six repetitive MRE examinations of the in vivo healthy brain demonstrated promising ability of the RD MRE to resolve local variations in mechanical properties of different brain tissue types. Preliminary results to date show that reconstructed real shear modulus and overall damping levels correlate well with the brain anatomical features. Quantified shear stiffness estimates for white and gray matter were found to be 3 kPa and 2.1 kPa, respectively. Due to the non-identifiability of the model at a single frequency, reconstructed RD based parameters limit any physical meaning. Therefore, MF-based and parametric-based cerebral RD elastography was also performed.
8
Sun, Weizhen. "Microstructure-based FE Modeling and Measurements of Magnetic Properties of Polymer Matrix-Metal Composites." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/74946.
Повний текст джерелаАнотація:
An increasing need for smaller, higher-power-density devices is driving the development of more advanced topologies for use in power architectures. The challenge, however, is to reduce the size of the passive components in circuit boards (e.g., the inductors), which are typically the most bulky. There are two ways to approach this problem. The first is to redesign the flux in the inductor in order to minimize its size; the second is to optimize the magnetic properties of the constituent magnetic materials, which include permeability, density, resistivity, core loss density, saturation magnetization value, fluidity, sintering temperature, and others. Compared to altering the nature of solid magnetic materials to reduce space constraints, modifying the magnetic composite is preferred.
The most popular candidates for use in magnetic composites are magnetic powders and polymer composites. In particular, when metal alloys are chosen as magnetic powders they have high initial permeability, high saturation magnetization values, but low electrical resistivity. Since polymers can serve as insulation materials, mixing metal alloys with polymers will increase electrical resistivity. The most common metal alloy used is nickel-iron (permalloy) and Metglas.
Since existing modeling methods are limited in (a) that multiphasic composites cannot be utilized and (b) the volume fraction of magnetic particles must be low, this investigation was designed to utilize FE (finite element) simulation to analyze how magnetic properties change with the distribution of permalloy powder or Metglas flakes in composites. The primary magnetic properties of interest in this study are permeability and core loss density. Furthermore two kinds of magnetic composites were utilized in this investigation: a benzocyclobutene (BCB) matrix-permalloy and a benzocyclobutene (BCB) matrix-permalloy-based amorphous alloy (Metglas 2705M) material.
In our FE simulations, a BCB matrix-permalloy composite was utilized in a body-centered cubic model with half-diameter smaller particles serving as padding. The composite was placed in a uniform magnetic field surrounded by a material whose relative permeability was equal to zero in simulation. In comparison to experimental results, our model was able to predict permeability of composites with volume fraction higher than 52%. It must be noted, however, that although our model was able to predict permeability with only 10% off, it was less effective with respect to core loss density findings. The FE model also showed that permeability will increase with an increasing volume fraction of magnetic particles in the composite. To modify the properties of the composite material, the model of the BCB matrix-permalloy-Metglas composite followed model simulations up to the point at which flakes were inserted in BCB matrix-permalloy composite. The thickness of flakes was found to be an important factor in influencing resulting magnetic properties. Specifically, when the thickness of flakes decreased to quarter size at the same volume fraction, the permeability increased by 15%, while core loss density decreased to a quarter of the original value. The analysis described herein of the important relationship between magnetic properties and the composites is expected to aid in the development and design of new magnetic composite materials.Master of Science
9
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.
Повний текст джерелаАнотація:
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
10
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.
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11
Gill, T. G. "Modifying the electronic properties and magnetic interactions of the two-dimensional material silicene." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1532889/.
Повний текст джерелаАнотація:
As the pursuit for more powerful electronic devices progresses, individual components have had to be produced at ever smaller dimensions. Today, conventional technologies are at the edge of feasibility as they approach a fundamental limit at the atomic scale. Much research is aimed at overcoming the barrier to atomic scale devices, and indeed some of the explosion of interest into two-dimensional materials over the past decade has its roots in this goal. Graphene, the first atomically thin two-dimensional material, has since been followed by a growing number of intriguing materials with a wide variety of interesting properties, many of which may prove useful in technological devices. One of these two-dimensional materials is silicene, the silicon analogue to graphene that shares many of its properties. Moreover, owing to it being made of silicon, it may be more easily integrated into existing industrial processes. In this thesis, silicene grown upon conductive zirconium diboride is investigated by scanning tunnelling microscopy and spectroscopy. It is found that the structural and electronic properties of epitaxial silicene can be fine-tuned by depositing small amounts of silicon on its surface. However, with continued silicon deposition a significant change is observed: the additional silicon leads to the formation of a layered metallic silicon nanostructure that could be utilised as an atomically precise metallic contact to silicene. Beyond this, the magnetic interactions of individual cobalt atoms on the silicene surface are investigated and it is found that the combination of the semiconducting silicene surface with the metallic zirconium surface yields an unusual spatially distributed Kondo effect. When cobalt atoms are in close proximity to one another on the silicene surface, they exhibit an incredibly strong indirect exchange (RKKY) interaction even at significant separations above 1 nm. The results in this thesis highlight the rich array of phenomena that can manifest in two-dimensional materials and point towards potential future developments for atomic scale electronic and spintronic devices.
12
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.
Повний текст джерелаАнотація:
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.
13
顧若愚 and Ruoyu Gu. "Physical properties of some magnetic systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31240173.
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Gu, Ruoyu. "Physical properties of some magnetic systems /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21981942.
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15
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.
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16
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.
Повний текст джерелаАнотація:
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).
17
Krings, Andreas. "Iron Losses in Electrical Machines - Influence of Material Properties, Manufacturing Processes, and Inverter Operation." Doctoral thesis, KTH, Elektrisk energiomvandling, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145243.
Повний текст джерелаАнотація:
As the major electricity consumer, electrical machines play a key role for global energy savings. Machine manufacturers put considerable efforts into the development of more efficient electrical machines for loss reduction and higher power density achievements. A consolidated knowledge of the occurring losses in electrical machines is a basic requirement for efficiency improvements. This thesis deals with iron losses in electrical machines. The major focus is on the influences of the stator core magnetic material due to the machine manufacturing process, temperature influences, and the impact of inverter operation. The first part of the thesis gives an overview of typical losses in electrical machines, with focus put on iron losses. Typical models for predicting iron losses in magnetic materials are presented in a comprehensive literature study. A broad comparison of magnetic materials and the introduction of a new material selection tool conclude this part. Next to the typically used silicon-iron lamination alloys for electrical machines, this thesis investigates also cobalt-iron and nickel-iron lamination sheets. These materials have superior magnetic properties in terms of saturation magnetization and hysteresis losses compared to silicon-iron alloys. The second and major part of the thesis introduces the developed measurement system of this project and presents experimental iron loss investigations. Influences due to machine manufacturing changes are studied, including punching, stacking and welding effects. Furthermore, the effect of pulse-width modulation schemes on the iron losses and machine performance is examined experimentally and with finite-element method simulations. For nickel-iron lamination sheets, a special focus is put on the temperature dependency, since the magnetic characteristics and iron losses change considerably with increasing temperature. Furthermore, thermal stress-relief processes (annealing) are examined for cobalt-iron and nickel-iron alloys by magnetic measurements and microscopic analysis. A thermal method for local iron loss measurements is presented in the last part of the thesis, together with experimental validation on an outer-rotor permanent magnet synchronous machine.QC 20140516
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Soliz, Jennifer Rose. "Investigating the Structural, Magnetic, and Electrical Properties for Novel Magnetic Materials." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1354733145.
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Calvo, de la Rosa Jaume. "Mechanical and functional properties in magnetic materials." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667865.
Повний текст джерелаАнотація:
This doctoral Thesis has been focused on the preparation of magnetic materials by different methods, the characterization of their structural characteristics, and the understanding of their mechanical and magnetic properties. Furthermore, a big effort has been paid to investigate the frequency-dependent functional properties of different materials, which are increasingly demanded in novel technological applications. Moreover, this work presents this characterization in a wide range of frequencies, from the kHz to the THz.
In the first chapter, the reader will find an introduction to the topic and the state of the art of those materials that have been synthesized and developed in this Thesis. Then, the general goals of our research are described.
Chapter II provides all the needed fundamental theory to accomplish with the previously stated goals. The concepts exposed here will be used later in the following chapters where the results will be shown and discussed. Moreover, this chapter does not only pretend to give the essential notions used in the following chapter, but we also aim to provide a useful guide to anyone who starts working on this field.
All the materials, devices, software, and experimental conditions used in this Thesis are described in Chapter III. Here, we describe these aspects in detail in order to allow an agile discussion in the following chapters.
The first experimental chapter is Chapter IV, where the synthesis of copper ferrite nanoparticles by mean of sol-gel and co-precipitation is described. The sol-gel process is optimized through of design of experiments (DoE) approach. The results of the mechanical and magnetic characterization of solid pellets fabricated with the previously synthesized nanoparticles are also shown in this chapter. Finally, by using statistical methods a direct experimental correlation between the mechanical and magnetic properties is found in this material.
Another material, a carbon nanotube–based nanocomposite, is studied in Chapter V. This novel material is first structurally characterized in order to understand its magnetic properties. A big effort is paid on the study of the magnetic relaxation of this material, which has not been previously reported as far as we know.
The investigation of soft magnetic materials (SMM) and composites (SMC) can be found in Chapter VI. The actual SMCs are first structurally and magnetically characterized. Their magnetic properties in the kHz and MHz frequency range are also investigated, showing the better performance of the SMC at high frequencies. In the second part of the chapter, the development on new SMC’s formulations is described. The developed materials are potentially useful for applications in the kHz and MHz frequency range.
The frequency is raised in Chapter VII. Terahertz time-domain spectroscopy (THz-TDS) is used to investigate the optical and dielectric properties of two different semiconductor oxides from 180 GHz to 3 THz. The signal processing and the interpretation of the effect that different characteristics of the sample may have on the observed properties are discussed. In this chapter, magnetic materials are not investigated because the Fresnel
model – which is the base of this technique - assumes a non-magnetic response of the material.
The work described in Chapter VIII is completely different from the previous ones. In this case, we investigate the manipulation of the magnetic moments by using surface acoustic waves (SAWs). The experiments done in this chapter lead to interesting observation about the potentiality of the use of SAWs to accelerate the magnetic moment reversal in magnetic nanoparticles.Esta Tesis Doctoral se centra en el estudio de materiales magnéticos en su conjunto, tanto desde la síntesis hasta sus propiedades mecánicas y funcionales finales. Además, ha habido un especial interés en el estudio de las propiedades funcionales en un amplio rango frecuencial. De este modo, en el primer capítulo, el lector puede encontrar una introducción al campo de investigación, así como también el estado del arte de aquellos materiales que se han sintetizado y desarrollado en esta Tesis. Por otro lado, en el Capítulo II se aportan todos los conceptos teóricos necesarios para el siguiente desarrollo de la Tesis. Además, los materiales, dispositivos, software y condiciones experimentales utilizados durante el desarrollo de esta investigación están descritos en el Capítulo III. El Capítulo IV es la primera parte experimental de la Tesis, y en la que se describe la síntesis de nanopartículas de ferrita de cobre vía sol-gel y coprecipitación. Además, se estudian las propiedades magnéticas y mecánicas en bulk, y se analiza su correlación empírica. El Capítulo V está dedicado al estudio de un nuevo material: un nanocompuesto magnético basado en nanotubos de carbono. Inicialmente se caracteriza química y estructuralmente para después centrarse en las propiedades magnéticas. Se realiza, además, un detallado estudio de su relajación magnética. Por otro lado, en el Capítulo VI, se investigan materiales magnéticos blandos. Inicialmente se analizan los materiales actualmente utilizados, mientras que en una segunda parte se desarrollan nuevas formulaciones con interesantes propiedades tecnológicas. En el Capítulo VII se presenta el estudio de las propiedades ópticas y dieléctricas en el rango de los THz. Se describe detalladamente el método, análisis de señal, y efecto de las características físicas de la muestra sobre la medida. Finalmente, también se propone un método para cuantificar el efecto de la porosidad de las muestras. Por último, el Capítulo VIII se investiga la manipulación del momento magnético mediante estímulos mecánicos como las ondas acústicas superficiales (SAW, en inglés). Se observa una clara variación experimental con la aplicación de las SAWs, y se relaciona matemáticamente esta variación con la frecuencia y potencia de las SAWs.
20
Scott, Robert William James. "Magnetic properties of thiogermanate open-framework materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ34035.pdf.
Повний текст джерела
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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.
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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.
Повний текст джерелаАнотація:
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
23
Hao, Yaowu 1969. "Magnetic properties of lithographically patterned thin film magnetic elements for magnetic random access memory applications." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29970.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.Includes bibliographical references (p. 133-139).
Interference lithography, together with ion beam etching or lift-off processes, has been utilized to produce large area periodic rectangular patterns. Single layer Co, NiFe, and multilayer Co/Cu/NiFe pseudo spin valve films have been patterned into series of element arrays with different sizes. With the aim of assessing the behavior of future magnetic random access memory (MRAM) devices, the magnetic properties of the patterned elements, including magnetization switching mechanisms, switching field distribution, magnetic thermal stability, and magnetostatic interactions, have been studied using magnetic force microscopy (MFM), SQUID magnetometer, alternating gradient magnetometer (AGM) and vibrating sample magnetometer (VSM). The measured results have been compared with the theoretical shape anisotropy theory to try finding a guideline for controlling magnetic properties of patterned elements.
by Yaowu Hao.
Ph.D.
24
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.
Повний текст джерелаАнотація:
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.
25
Jung, Wonjoon. "Magnetic properties of small multi-layered rings." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42135.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references.
Thin film rings can be an alternative geometry of magnetic memory cells, in which data bits are stored by the chirality of the flux-closed or 'vortex' state of the ring. The absence of the stray field in the vortex state is advantageous of high density data storage. Elliptical rings with 3 / 2 pm major / minor diameter and widths of 300 nm above were fabricated from multi-layer thin film structures such as the ferromagnetic-antiferromagnetic exchange bias bilayer or giant magnetoresistance (GMR) spin valve structure, and their magnetic and magnetoelectric properties were investigated. Exchange-biased elliptical rings show an interplay between shape anisotropy and exchange anisotropy. When both the exchange bias and applied field are oriented along the major axis, an elliptical ring shows a shifted hysteresis loop and strong in-plane anisotropy. The switching behavior and vortex state stability of the rings are strongly dependent on the pinning direction and applied field direction relative to the major axis of the ellipse. It has proven difficult to control the vortex chirality in a simple manner. A model is described that predicts the vortex chirality of an elliptical magnetic ring as a function of the direction of the applied field and of the exchange bias, based on the change in the energy of the system as the domain walls move. Experimental measurements of the chirality in Co and Co / IrMn magnetic rings with a 3.2 pm major axis are in excellent agreement with the model.
(cont.) The vortex circulation direction can therefore be tailored with an appropriate combination of the applied field direction and exchange bias direction with respect to the major axis. NiFe / Cu / Co / IrMn spin valve elliptical rings with 3.2 / 1.9 pm major / minor diameter and the width of 340 - 370 nm were fabricated and the magnetoresistance (MR) of the rings were measured with applying an in-plane field. Spin valve rings show asymmetric MR curves with three different MR states. Minor loop MR measurements, which give rise to switching of only the free layer of the spin valve ring, demonstrate that an individual control of the vortex chirality in each ferromagnetic layer is possible in a ring-shaped multilayered structure, such as a spin valve ring.
by Wonjoon Jung.
Ph.D.
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Zadik, Ruth Helen. "Structural, electronic and magnetic properties of fulleride materials." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/11187/.
Повний текст джерелаАнотація:
This thesis outlines new research findings into the solid-state properties of selected alkali- and alkaline-earth-intercalated fullerides, focusing on their structural, electronic and magnetic properties at ambient and non-ambient temperatures and pressures, primarily employing synchrotron X-ray powder diffraction and SQUID magnetometry. Understanding the relationship between superconducting, neighbouring insulating and normal metallic states above Tc in unconventional superconductors is fundamentally important. Highly expanded fcc Cs3C60 behaves very differently to underexpanded A3C60 alkali fullerides such as K3C60 and Rb3C60. Whilst superconductivity in the latter seems well described by conventional Bardeen-Cooper-Schrieffer (BCS) theory, Cs3C60, a Mott-Jahn-Teller insulator under ambient pressure, exhibits distinctly non-BCS type superconductivity upon pressurisation. The intermediate regime adjacent to the Mott boundary, where strong electronic correlations are prominent, was hitherto only studied through physical pressurisation of Cs3C60 to tune the intermolecular spacing. This thesis reports the solid-state synthesis of fcc-rich RbxCs3−xC60 (0.25 ≤ x ≤ 2) bulk superconducting materials, with excellent stoichiometry control, and the effects on the electronic properties in situ of tuning intermolecular separation by varying temperature, physical and chemical pressurisation via adjusting the cation dopant ratio. It is shown that the Mott boundary can be traversed at ambient pressure upon cooling, and the metal-insulator crossover temperature tuned by chemical and physical pressurisation. A15 Cs3C60 orders antiferromagnetically below 46 K. Previous studies found no evidence of symmetry lowering or discontinuous structural changes upon magnetic ordering, despite theoretical predictions to the contrary. This issue is addressed with the first systematic ultrahigh-resolution investigation of its structural evolution with temperature, evidencing a transition to a rhombohedral phase below TN. The structural properties of A15 Cs3C60 and Ba3C60 in situ upon pressurisation are described, extending previous work on A15 Cs3C60. This first study of the effects of compression on the latter system reveals a pressure-induced structural transition to a hitherto unreported monoclinic phase.
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Singley, Edward Jason. "Infrared properties of novel electronic and magnetic materials /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2002. http://wwwlib.umi.com/cr/ucsd/fullcit?p3061624.
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Akamatsu, Hirofumi. "Magnetic Properties of Amorphous Oxides and Related Materials." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/77993.
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Khosrowbeygi, Borchalooei Abolfazi. "A new free-wave technique for measuring material dielectric and magnetic properties at millimetre wavelengths." Thesis, University College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265341.
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Tang, Cheng. "Computational exploration of two-dimensional materials with novel electronic, optical and magnetic properties." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/212532/1/Cheng_Tang_Thesis.pdf.
Повний текст джерелаАнотація:
This project was a step forward in discovering new two-dimensional (2D) structures for electronic and spintronic applications. This work comprehensively investigates seven intriguing 2D structures with novel electronic, optical and magnetic properties on the basis of the global structural search and first-principles calculations. These findings not only highlight the promising materials platforms for advanced nanodevices but also provide the theoretical guides for designing multifunctional 2D materials.
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Lu, Cong. "Epitaxial growth and intrinsic magnetic properties of magnetic thin films on semiconductor materials." Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/9987/.
Повний текст джерелаАнотація:
Spin electronics, or spintronics, is an emergent interdisciplinary area whereby the spin degree of freedom in electronic devices is employed. One of the most important topics of spintronics is to develop magnetic/semiconductor hybrid materials for the next generation spin devices such as Spin-FET. This dissertation investigates the magnetic properties of magnetic thin films deposited on semiconductor substrate. Fe and Ni films have been deposited onto GaAs substrate with different substrate treatment. Both single and poly crystalline samples were developed during the process, and the magnetic properties were compared to explore the differences. The origin of a uniaxial magnetic anisotropy (UMA) from the crystal symmetry of the bcc Fe, observed in Fe/GaAs (100) has been investigated. Another major work for this thesis is the Artemis TR-ARPES (time resolved – angular resolved photoemission spectroscopy) project in Rutherford Appleton Laboratory. Successful MBE growth was achieved for the first time during the Artemis TR-ARPES project, followed by static and time-resolved MOKE, and time-resolved photoemission measurements. Preliminary time-resolved photoemission spectroscopy measurements has been performed on the single crystal Fe samples, which is the world first result in term of the study of the time-dependent valence band structures using direct photoemission technique from a metallic material. The research finally extended to the CoFeB film on GaAs substrate. The discovery of uniaxial magnetic anisotropy of this amorphous film make it one of the hottest topic in research. XMCD measurements were conducted and the results went through a series of calculations gives an indication of the relation between magnetic moment to the anisotropy. TEM inspections offers a clear look at the interface of the samples.
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Lees, Joan Anne. "Modelling the magnetic properties of natural and environmental materials." Thesis, Coventry University, 1994. http://curve.coventry.ac.uk/open/items/aa273a60-0c0d-a613-81b9-b95cc2ec3fdd/1.
Повний текст джерелаАнотація:
Magnetic properties have been used to characterize natural and environmental materials. An evaluation of magnetic properties, for the modelling of sources of materials and minerals, has been completed. A methodological framework has been developed for the application of magnetic techniques to studies involving the quantification of sources of materials and minerals in any environment. the framework includes the idntification of sources using magnetic reconnaissance and multi-variate statistical classification techniques. magnetic measurements used are susceptibility (both field and laboratory), remanence and magnetization measurements. the linear additivity of magnetic measurements, and classification and linear modelling techniques, ahve been tested using datea for artificial laboratory mixtures and hypothetical mixing experimentrs. The limitations of using magnetic properties with these statistical and mathematical techniques are defined. the famework allows for hte testing of suitabililty of manetic modelling techniques in any sourceing study.
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Saureu, Artesona Sergi. "From mononuclear to dinuclear : magnetic properties of transition metals complexes." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/386451.
Повний текст джерелаАнотація:
En les darreres dècades, el món de la tecnologia i el desenvolupament de nous aparells electrònics s'han convertit en vitals per la nostra societat. Considerant la creixent demanda per la interpretació de resultats experimentals, la millora dels mètodes teòrics i el creixement dels recursos computacionals ens han permés un millor enteniment del comportament magnètic en sistemes amb metalls de transició. L'objectiu d'aquesta tesi és contribuir en aquest camp d'investigació amb l'estudi de materials magnètics utilitzant eines computacionals (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), i en alguns casos, combinant-ho amb resultats experimentals. La primera part (Capítols 3 i 4) inclou l'estudi dels estats electronics de complexes de spin-crossover de Fe(II) i Fe(III) combinant la teoria funcional de la densitat (DFT i TD-DFT) amb mètodes multiconfiguracionals (CASSCF, CASPT2). A més a més, utilitzant la mateixa combinació, hem descrit el fenomen LIESST en complexes de Fe(III). La segona part (Cap. 5 i 6) exposa l'estudi de les propietats magnètiques associades a l'acoblament magnètic utilitzant mètodes variacionals (DDCI, DDCI-2), en un complex de Fe(IV) i un complex bimetàl·lic [MnCr]-oxalat, y com els canvis estructurals afecten a aquest acoblament. Altrament, hem fet un rigurós anàlisi de l'estructura electrònica del complex de Fe(IV) per proporcionar més informació en la descripció més adequada del sistema.En las últimas décadas, el mundo de la tecnologia y el desarrollo de nuevos aparatos electrónicos se han convertido en vitales para nuestra sociedad. Considerando la creciente demanda para la interpretación de resultados experimentales, la mejora de los métodos teóricos y el crecimiento de los recursos computacionales nos han permitido un mejor entendimiento de los comportamientos magnéticos en los sistemas con metales de transición. El objetivo de esta tesis es contribuir a este campo de investigación con el estudio de materiales magnéticos usando herramientas computacionales (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), y en algunos casos, combinando con resultados experimentales. La primera parte (Capítulo 3 y 4) incluye el estudio de los estados electrónicos de los complejos de spin-crossover de Fe(II) y Fe(III) combinando la teoria funcional de la densidad (DFT y TD-DFT) con métodos multiconfiguracionales (CASSCF, CASPT2). Además, usando la misma combinación, hemos descrito el fenómeno LIESST en complejos de Fe(III). La segunda parte (Cap. 5 y 6) expone el estudio de las propiedades magnéticas asociadas al acoplamiento magnético utilizando metodos variacionales (DDCI, DDCI-2), en un complejo de Fe(IV) y un complejo bimetálico [MnCr]-oxalato, y como los cambios estructurales afectan a ese acoplamiento. Por otra parte, hemos hecho un riguroso analisis de la estructura electrónica del complejo de Fe(IV) para aportar la información para la descripción mas adecuada del sistema.
Over the last decades the world of technology and the development of new devices have become vital for our society. Considering the growing demand for interpretation of experimental observations, the improvement of theoretical methods and the increasing of the computational resources has allowed us to deepen the understanding of magnetic beahvior of metal transitions architectures. The aim of this thesis is to contribute to this research field with the study of magnetic materials by using computational tools (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), and in some cases combining it with experimental results. The first part (Chapters 3 and 4) includes the study of the electronic states of Fe(II) and Fe(III) spin-crossover complexes combining the density functional theory (DFT and TD-DFT) with multiconfigurational methodologies (CASSCF, CASPT2). In addition, we have described the LIESST phenomenon in Fe(III) using the same combination. The second part (Chapters 5 and 6) exposes the study of the magnetic properties related to the magnetic coupling using variational methods (DDCI, DDCI-2) of a Fe(IV) complex and bimetallic [MnCr] oxalate-based complexes and how changes can influence to the coupling. Moreover, a rigorous analysis of the electronic structure of the Fe(IV) system has been performed to provide more information about the most adequate description of the system in terms of intuitive chemical concepts.
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Black, Serra Ashley Phillip. "New oxynitride materials with luminescent, magnetic and catalytic properties." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/405378.
Повний текст джерелаАнотація:
En les darreres dècades els oxinitrurs han rebut un interès creixent degut al vast rang d'aplicacions en els quals han mostrat una aplicabilitat potencial. Destaquen les seves propietats com fotocatalitzadors actius en el visible en processos de fotòlisi d'aigua, pigments inorgànics no tòxics, fòsfors per a LEDs (light emitting diodes) de llum blanca, materials amb magneto resistència colossal i materials dielèctrics o ferroelèctrics.
En aquesta tesi presentem la síntesi i caracterització de dos nous fòsfors amb potencial aplicació en tecnologia LED de llum blanca. Els oxinitrursilicats LaSrSiO3N i LaBaSiO3N quan són activats amb Eu2+ emeten llum de color vermell ataronjat sota excitació amb radiació blava o UV. La solució sòlida Sr2-xLaxSiO4-xNx (0 ≤ x ≤ 1) es pot obtenir per la substitució concomitant de Sr2+ per La3+ i O2- per N3- en l’òxid Sr2SiO4. Mitjançant el control de la composició, es pot modificar el color de l'emissió des del grog (x = 0.2) fins a vermell ataronjat (x = 1) quan es dopa amb Eu2+ i des del blau verdós (x = 0.2) fins taronja groguenc (x = 1) quan es dopa amb Ce3+.
D'altra banda, aquesta tesi també ha tingut com a objectiu la síntesi i estudi de nous oxinitrurs amb estructura de perovskita extenent el rang d’aquest grup de compostos als metall de transició Cr i Hf.
Les perovskites LnCrO3-xNx amb Ln = La, Pr, Nd i continguts de nitrogen fins x = 0.59 van ser sintetitzats per mitjà de la amonòlisis dels precursors LnCrO4. La substitució d'oxigen per nitrogen indueix l'oxidació de Cr3+ a Cr4+ com a mecanisme de compensació de càrrega i les conseqüències que comporta sobre les propietats magnètiques han sigut investigades. El dopatge amb forats en les perovskites LnCrO3 produït mitjançant la substitució dels anions O2- per N3- suprimeix l'ordre magnètic però menys dràsticament que quan és induït per la substitució catiònica de Ln3+ per M2+ (M = Ca, Sr ).
Finalment, presentem la síntesi, caracterització estructural i l'estudi de les propietats elèctriques i fotocatalítiques dels nous oxinitrurs amb estructura de perovskita de hafni LnHfO2N (Ln = La, Pr, Nd, Sm) i del compost anàleg LaZrO2N. Aquests materials cristal·litzen en una estructura ròmbica de tipus GdFeO3 i presenten band gaps entre 3.4 i 2.8 eV. L'evolució d'H2 i O2 produïda sota la il·luminació amb radiació d'un llum de Xenó de 300 W va demostrar que les perovsquites de hafni tenen els potencials de reducció i oxidació adequats per dur a terme dissociació de la molècula d'aigua en presència dels convenients agents de sacrifici. Les mesures de permitivitat dielèctrica i resistivitat elèctrica van mostrar que els compostos LnHfO2N (Ln = La, Pr, Nd, Sm) són aïllants elèctrics amb constants dielèctriques entre 16 i 30 a temperatura ambient.In recent years oxynitride materials have received increasing attention because of their emerging applications as photocatalysts, phosphors, pigments, dielectrics and magnetic materials. This thesis reports the synthesis and characterization of two new oxynitride phosphors with potential application in warm white light LED technologies. The new compounds LaSrSiO3N and LaBaSiO3N activated with Eu2+ are orange-red light-emitting luminescent materials under excitation in the UV-blue range. We also report that the solid solution Sr2-xLaxSiO4-xNx (0≤ x ≤1), can be obtained by concomitant substitution of Sr2+ by La3+ and O2- by N3- in Sr2SiO4. By controlling the composition the emission colours can be tuned from yellow (x = 0.2) to orange-red (x = 1) for Eu2+ phosphors and from blue-green (x = 0.2) to orange-yellow (x = 1) in Ce3+ doped samples. On the other hand, this thesis has been directed towards the synthesis and study of new oxynitride perovskites extending the range of this group of compounds to the transition metals Cr and Hf. LnCrO3-xNx perovskites with Ln = La, Pr and Nd and nitrogen contents up to x = 0.59 have been synthesised through ammonolysis of LnCrO4 precursors. Nitride substitution induces oxidation of Cr3+ to Cr4+ as the mechanism of charge compensation and the consequences of this on magnetic ordering transitions have been studied. Hole-doping through O2-/N3- anion substitution suppresses magnetic order but far less drastically than Ln3+/M2+ (M = Ca, Sr) cation substitutions. Finally, we show the synthesis, structure, electrical and photocatalytic properties of new hafnium oxynitride perovskites LnHfO2N where Ln= La, Pr, Nd and Sm, and the previously reported analogous compound LaZrO2N. They crystallize in the orthorhombic GdFeO3-type superstructure and show band gaps between 3.4 and 2.8 eV. The time course of O2 and H2 evolution under Xenon lamp 300 W irradiation showed that the hafnium perovskites have the adequate oxidation and reduction potential to conduct the overall water splitting reaction in presence of a sacrificial agent. Dielectric and resistivity measurements showed that both Hf and Zr perovskite oxynitrides are electric insulators with dielectric constants between 16 and 30 at room temperature.
35
Gu, Ziyan. "Local magnetic susceptometry : visualizing functional properties of novel materials /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-265.
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36
Margiolaki, Irene. "Structural, magnetic and dynamic properties of fullerene based materials." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288785.
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Parmar, Baljit Singh. "The preparation and properties of nanocrystalline soft magnetic materials." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284381.
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Milford, Gabrielle Helen. "Moessbauer spectroscopic studies of the magnetic and structural properties of novel nanophase magnetic materials." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343589.
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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.
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Broddefalk, Arvid. "Magnetic properties of transition metal compounds and superlattices." Doctoral thesis, Uppsala University, Department of Materials Science, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-535.
Повний текст джерелаАнотація:
Magnetic properties of selected compounds and superlattices have been experimentally studied using SQUID (superconducting quantum interference device) and VSM (vibrating sample magnetometer) magnetometry, neutron diffraction and Mössbauer spectroscopy measurements combined with theoretical ab initio calculations.
The magnetic compounds (Fe1-xMx)3P, M=Co or Mn have been studied extensively. It was found that Co can substitute Fe up to x=0.37. Increasing the Co content leads to a reduction of the Curie temperature and the magnetic moment per metal atom. Mn can substitute Fe up to x=0.25 while Fe can be substituted into Mn3P to 1-x=0.33. On the iron rich side, the drop in Curie temperature and magnetic moment when increasing the Mn content is more rapid than for Co substitution. On the manganese rich side an antiferromagnetic arrangement with small magnetic moments was found.
The interlayer exchange coupling and the magnetocrystalline anisotropy energy of Fe/V superlattices were studied. The coupling strength was found to vary with the thickness of the iron layers. To describe the in-plane four-fold anisotropy, the inclusion of surface terms proved necessary.
The in-plane four fold anisotropy was also studied in a series of Fe/Co superlattices, where the thickness of the Co layers was kept thin so that the bcc structure could be stabilized. Only for samples with a large amount of iron, the easy axis was found to be [100]. The easy axis of bulk bcc Co was therefor suggested to be [111].
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Supplee, William Wagner. "Structural, magnetic, and optical properties of orthoferrite thin films." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/44813.
Повний текст джерелаАнотація:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (leaves 41-43).
Pulsed laser deposition was used to create thin films of Ce-Fe-O and Y-Fe-O systems. Deposition temperature and ambient oxygen pressure were varied systematically between samples to determine which deposition conditions were most favorable to the formation of cerium/yttrium orthoferrite. The structure and composition of each film were then determined using X-ray diffraction and wavelength dispersive spectroscopy respectively. In addition, the magnetic and optical properties of the yttrium films were characterized to determine the suitability of these materials as Faraday isolators at A=1550 nm. Results show that orthoferrite crystal structures in these systems are not stable in the temperature and oxygen ranges tested. It was also found that increasing oxygen pressure caused exponential decay in the deposition rate. Most films were amorphous, exhibiting a paramagnetic M-H plot and a Verdet coefficient between 0.37 and 0.89 deg cm-1 Gauss-1
by William Wagner Supplee, Jr.
S.B.
42
Krueger, Elizabeth A. S. B. Massachusetts Institute of Technology. "Characterization of Kenyan obsidian through analysis of magnetic properties." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/89968.
Повний текст джерелаАнотація:
Thesis: S.B. in Archaeology and Materials, Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 46-49).
Obsidian is known to have been used for tool making in Kenya since the Early Stone Age, appearing as early as 974 thousand years ago (Durkee and Brown, in press). Past research has shown that the study of obsidian artifacts, and the determination of their provenance, can be very useful in reconstructing past civilizations and analyzing the spread of technology and trade. A number of different analytical techniques have previously been utilized to characterize obsidian sources for such studies, including magnetic analysis. This thesis reports the results of a preliminary study to explore the potential of utilizing magnetic analysis for the characterization of obsidian sources in Kenya. A total of 192 samples from 23 localities, belonging to 6 broadly defined petrologically distinct source groups, were analyzed using a vibrating sample magnetometer to test saturation magnetization (Ms), remanence magnetization (Mr), and coercivity (Hc). Comparing the ratio of Mr/Ms with Hc allowed clear differentiation among three of the analyzed obsidian sources (Groups 14, 19, and 29 from Merrick and Brown 1984a). The magnetic signatures reveal clues about the microscopic Fe mineral grains present in the samples, suggesting that magnetic characterization also has the potential to provide additional value as a supplementary technique to chemical analysis. Based on these preliminary results, it is proposed that future studies could examine the temperature dependence of the magnetic properties of obsidian to provide more complete characterization of the obsidian sources.
by Elizabeth A. Krueger.
S.B. in Archaeology and Materials
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Пазуха, Ірина Михайлівна, Ирина Михайловна Пазуха, Iryna Mykhailivna Pazukha, and K. S. Levchenko. "Magnetoresistive Properties of Py/Ag/Co Pseudo Spin-valves." Thesis, Sumy State University, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67956.
Повний текст джерелаАнотація:
The pseudo spin-valve (PSV) structures based on soft magnetic permalloy Ni80Fe20 (Py) and hard magnetic Co, separated by a layer of nonmagnetic material (Ag) belong to the pseudo spin-valve structures, in which independent magnetization reversal of magnetic layers is gained by diverse coercive forces of magnetic layers.
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ATZORI, MATTEO. "Anilate-based Functional Molecular Materials with Conducting and Magnetic Properties." Doctoral thesis, Università degli Studi di Cagliari, 2015. http://hdl.handle.net/11584/266558.
Повний текст джерелаАнотація:
This work reports on the design, synthesis and characterization of novel anilate-based
functional molecular materials showing magnetic and conducting properties.
The family of anilate ligands comprises several derivatives obtained by introducing various
substituents (H, F, Cl, Br, I, CN, Me, NO2, etc.) at the 3 and 6 positions of a common 2,5-dihyroxy-
1,4-benzoquinone framework. Their electronic/structural features, coordination modes and
ability to mediate magnetic exchange interactions between coordinated metal centers make
them suitable candidates for the preparation of the above-mentioned materials.
In Chapter 1, the syntheses of novel anilate-based ligands (anilate = An) having thiophene (Th),
3,4-ethylenedioxy-thiophene (EDOT), or Cl/CN as substituents are presented, along with their
crystal structures, the investigation of the emission (Cl/CN derivative) or charge-transfer (Th,
EDOT derivatives) properties and preliminary coordination chemistry studies.
Chapter 2 reports on a general synthetic strategy to achieve rationally designed tris-chelated
octahedral paramagnetic metal complexes, based on the combination of CrIII and FeIII as metal
ions with chloranilate, bromanilate, iodanilate, hydranilate and chlorcyananilate as ligands.
The crystal structure analyses, spectroscopical and electrochemical features, density functional
theory calculations, and the magnetic properties of these metal complexes of general formula
[A]3[MIII(X2An)3] (A = (n-Bu)4N+, (Ph)4P+; MIII = Cr, Fe; X = Cl, Br, I, H, Cl/CN) are described.
In Chapter 3 a novel class of molecule-based ferrimagnets formulated as [A][MnIIMIII(X2An)3] (A
= [H3O(phz)3]+, (n-Bu)4N+; MIII = Cr, Fe; X = Cl, Br, I, H), obtained according to the “complex-asligand”
approach by combining MnII metal ions with the [M(X2An)3]3- molecular building blocks
described in Chapter 2, is reported. The crystal structures and the magnetic properties for
these compounds are described, and the structure/properties correlation observed between
the ordering temperature values and the electron density on the ligand ring, associated with
the electron withdrawing properties of the X substituents, is particularly highlighted.
Chapter 4 reports on the structural diversity and the physical properties of three new
paramagnetic molecular conductors obtained combining the BEDT-TTF organic donor and the
[Fe(Cl2An)3]3- metal complex as conducting and magnetic building blocks, respectively. The
correlation between the crystal structure and conductivity behavior is reported.
Finally, in Chapter 5, the crystal structures and the physical properties of a complete series of
isostructural chiral molecular conductors obtained by combining the TM-BEDT-TTF organic
donor in its (S,S,S,S) and (R,R,R,R) enantiopure forms, or their racemic mixture (rac), with 2D
heterobimetallic anionic layers obtained in situ by association of tris(chloranilato)ferrate(III)
metal complexes and potassium cations are described.
As far as the framework of the thesis is concerned, this work is organized as follows. Part I
contains a general introduction on molecular materials, the state of the art and the aim of the
work. Part II contains the obtained results and their discussion divided in 5 Chapters whose
content has been summarized above. Part III contains the conclusions and the perspectives for
this work. Finally, Part IV contains 5 Appendixes where additional information (basic principles
of conductivity and magnetism, details on the electrocrystallization technique, etc.) are given.
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Karimi, Roman [Verfasser], and Martin [Akademischer Betreuer] Dressel. "New permanent magnetic materials : efficient search, microstructure and magnetic properties / Roman Karimi ; Betreuer: Martin Dressel." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1176521527/34.
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Hudson, Guy Frederick, and Guy Frederick Hudson. "Surface chemistry of magnetic oxides and ferrites and their interaction with selected components of magnetic inks." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184919.
Повний текст джерелаАнотація:
Studies to compare and elucidate some of the surface chemical characteristics of chromium dioxide and barium ferrite magnetic particles have been performed. These investigations primarily involved using the technique of flow microcalorimetry to look at the interaction of molecular probes (pyridine, 4-nitrophenol) and various components present in a magnetic ink (dispersants and model binder compounds) with the particles. The interactions were measured in terms of heats of adsorption and adsorption density. Ancillary experiments using FTIR and XPS were also performed. Both electrophoretic measurements and calorimetric studies showed that stabilized CrO₂ was less acidic than un-stabilized CrO₂. Similar measurements showed that un-doped barium ferrite was more acidic than Co and Ti doped barium ferrite. The interactions of dispersants and model binder components with barium ferrite were found to be very exothermic; heats of interaction of greater than -20 kcal/mole were not uncommon. Subsequent analysis of barium ferrite particles treated with dispersants and binder compounds using FTIR and XPS suggested that these compounds formed chemical complexes on the surface of the ferrite particles.
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Nicolas, Ubrig. "Optical properties of carbon based materials in high magnetic fields." Phd thesis, Université Paul Sabatier - Toulouse III, 2011. http://tel.archives-ouvertes.fr/tel-00646148.
Повний текст джерелаАнотація:
La découverte des nanotubes de carbone, il y a maintenant une vingtaine d'années, a été un des moteurs de la recherche des nanotechnologies. Ces particules illustrent l'amalgame entre le monde macroscopique et le monde appelé nano. Cette discipline a également relancée la recherche sur le graphite et le carbone en général, qui atteint un nouveau sommet avec la découverte du graphène, une monocouche de graphite. Rapidement la physique des nanotubes et du graphène ont suscité l'intérêt d'être étudié sous champ magnétique avec la découverte de l'effet Aharonov-Bohm dans les nanotubes ou l'effet hall quantique dans le graphène. Cette thèse a pour but d'approfondir la connaissance des propriétés optiques des nanotubes, du graphène et du graphite sous champ magnétique intense. Pour cela nous nous interesserons dans un premier temps à la problématique des excitons sombres. Nous étudierons ensuite les propriétés magnétiques et dynamiques des tubes. La famille métallique est paramagnétique le long de son axe et diamagnétique perpendiculaire à celui-ci. La famille semiconductrice est diamagnétique par rapport à ces deux orientations mais la valeur perpendiculaire est plus élevée. De ce fait tous les nanotubes vont s'aligner parallèlement à un champ magnétique appliqué. Nous utiliserons des méthodes de spectroscopie optique pour étudier ce phénomène. La deuxième partie de la thèse consistera à examiner les propriétés optiques du graphène et du graphite et plus précisément les transitions entre niveaux de Landau sous champs intenses. La particularité du graphène est que ses porteurs de charge se comportent comme des particules relativistes avec une masse nulle. Les niveaux de Landau se trouvent modifiés avec une dépendance en racine du champ magnétique, par rapport aux systèmes deux dimensionels classiques, où l'on retrouve une dépendance linéaire comme pour l'électron libre par exemple. Ceci nous entrainera également à reéxaminer les propriétés du graphite et d'approfondir les connaissances, notamment à champ très élevé, sur ce matériau à priori bien connu et étudié dans le passé.
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Belk, Nathan. "Electronic transport and magnetic properties of disordered high-Tc materials." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10745.
Повний текст джерела
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Ubrig, Nicolas. "Optical properties of carbon based materials in high magnetic fields." Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1627/.
Повний текст джерелаАнотація:
La découverte des nanotubes de carbone, il y a maintenant une vingtaine d'années, a été un des moteurs de la recherche des nanotechnologies. Ces particules illustrent l'amalgame entre le monde macroscopique et le monde appelé nano. Cette discipline a également relancée la recherche sur le graphite et le carbone en général, qui atteint un nouveau sommet avec la découverte du graphène, une monocouche de graphite. Rapidement la physique des nanotubes et du graphène ont suscité l'intérêt d'être étudié sous champ magnétique avec la découverte de l'effet Aharonov-Bohm dans les nanotubes ou l'effet hall quantique dans le graphène. Cette thèse a pour but d'approfondir la connaissance des propriétés optiques des nanotubes, du graphène et du graphite sous champ magnétique intense. Pour cela nous nous interesserons dans un premier temps à la problématique des excitons sombres. Nous étudierons ensuite les propriétés magnétiques et dynamiques des tubes. La famille métallique est paramagnétique le long de son axe et diamagnétique perpendiculaire à celui-ci. La famille semiconductrice est diamagnétique par rapport à ces deux orientations mais la valeur perpendiculaire est plus élevée. De ce fait tous les nanotubes vont s'aligner parallèlement à un champ magnétique appliqué. Nous utiliserons des méthodes de spectroscopie optique pour étudier ce phénomène. La deuxième partie de la thèse consistera à examiner les propriétés optiques du graphène et du graphite et plus précisément les transitions entre niveaux de Landau sous champs intenses. La particularité du graphène est que ses porteurs de charge se comportent comme des particules relativistes avec une masse nulle. Les niveaux de Landau se trouvent modifiés avec une dépendance en racine du champ magnétique, par rapport aux systèmes deux dimensionels classiques, où l'on retrouve une dépendance linéaire comme pour l'électron libre par exemple. Ceci nous entrainera également à reéxaminer les propriétés du graphite et d'approfondir les connaissances, notamment à champ très élevé, sur ce matériau à priori bien connu et étudié dans le passéCarbon nanotubes are unique nano-objects with highly anisotropic electrical, magnetic and optical properties. In the past years the physics of carbon nanotubes made important steps toward the comprehension of its various complex physical properties. The optical response of nanotubes is driven by excitons. Of the sixteen possible exciton states only one decays radiatively. However a magnetic field can brighten one of the dark states. The aim of the first part of this thesis investigates the issue of the brightening of dark excitons. In the second part we use the magnetic properties of single walled carbon nanotubes to investigate their dynamic alignment in a pulsed magnetic field. Semiconducting tubes are diamagnetic both along and perpendicular to their long axis but the magnitude of the perpendicular susceptibility is higher. Metallic tubes are paramagnetic along their long axis and diamagnetic perpendicular to it. This constrains SWNT to align parallel to a magnetic field. Our data will be analysed with the aid of a theoretical model based on rotational diffusion of rigid rods. In the third part we study the magneto-optical properties of epitaxially grown multi-layer graphene. The Landau levels of graphene are different from standard two dimensional electron gases. They show a sqrt{B}dependence due to the relativistic nature of their charge carriers. We measure the system at high fields and high energies to probe the limit of massless Dirac fermions. The discovery of massless relativistic particles in graphene, a mono-layer of graphite, has completely renewed the interest in graphite. As a matter of fact graphite the optical properties of graphite are best described by bi-layer graphene. We show that the magneto-transmission experiments on thin graphite are in very good agreement with an effective bi-layer model. In addition we observe a non-predicted double structure in the graphene-like transitions which is not reported before
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Atzori, Matteo. "Anilate-based Functional Molecular Materials with Conducting and Magnetic Properties." Thesis, Angers, 2015. http://www.theses.fr/2015ANGE0009/document.
Повний текст джерелаАнотація:
Ce travail de thèse explore la capacité des ligands anilates d’être employés pour la préparation de nouveaux matériaux moléculaires fonctionnels avec des propriétés magnétiques et de conduction électrique. Les anilates, qui sont les dérivés du 2,5-dihydroxy-1,4- benzoquinone substitués sur les positions 3 et 6, ont été sélectionnés comme ligands puisque leurs caractéristiques électroniques et structurales, leurs modalités de coordination et leur capacité de médiation des interactions de super-échange magnétique en font d’excellents ligands pour la préparation de ces matériaux. Plusieurs ligands anilates ont été utilisés pour le design et la préparation d'une nouvelle classe de complexes paramagnétiques octaédriques tris-chélates de formule générale [MIII(X2An)3]3- (MIII = Cr, Fe; X = Cl, Br, I, H, Cl/CN, An = C6O4 2- = anilate). Ces complexes métalliques paramagnétiques ont été complètement caractérisés et utilisés comme briques moléculaires pour la préparation de i) une nouvelle classe de ferriaimants moléculaires, dans laquelle la modification des substituants sur le ligand permet de modifier les interactions entre les centres métalliques, et, par conséquent, les propriétés magnétiques, ii) des conducteurs paramagnétiques moléculaires obtenus par combinaison avec le donneur organique BEDT-TTF, iii) une série de conducteurs moléculaires chiraux obtenus par combinaison du donneur organique TM-BEDT-TTF avec des couches hétéro-bimétalliques anioniques obtenues par association in situ de complexes tris(chloranilate)ferrate(III) et des ions potassium. En outre, ont été synthétisés de nouveaux dérivés anilates avec des propriétés electroactives et de luminescence, afin de démontrer la capacité du motif anilate d’être fonctionnalisé avec différents substituants comme porteurs de propriétés physiques spécifiquesThis work explores the potential of anilate-based ligands in the synthesis of new rational designed functional molecular materials exhibiting improved magnetic and conducting properties. Anilates, namely 3,6-disubstitued 2,5-dihyroxy-1,4- benzoquinones in their dianionic form, have been selected as ligands since their electronic/structural features, coordination modes and ability to mediate magnetic exchange interactions between coordinated metal centers make them potential candidates for the preparation of theabove-mentioned materials. Various anilate derivatives have been used for the preparation of a family of rationally designed tris-chelated octahedral paramagnetic metal complexes of general formula [MIII(X2An)3]3- (MIII = Cr, Fe; X = Cl, Br, I, H, Cl/CN, An = C6O4 2- = anilate). These paramagnetic metal complexes have been thoroughly characterized and used, in turn, as molecular building blocks for the preparation of i) a family of molecule-based magnets, where subtle changes in the nature of the substituents on the anilate moiety were employed as “adjusting screws” in tuning the magnitude of the magnetic interaction between the metals, and thus, the magnetic properties, ii) hybrid paramagnetic molecular conductors in combination with the BEDT-TTF organic donor, iii) a complete series of isostructural chiral molecular conductors obtained by combining the TMBEDT- TTF chiral donor with 2D heterobimetallic anionic layers obtained in situ by the self-assembling of tris (chloranilato)ferrate(III) metal complexes and potassium cations.Moreover, novel anilate derivatives showing electroactive and luminescent properties have been further synthesized, highlighting the versatility of the anilate moiety to be functionalized with suitable substituents carrying selected physical properties