Dissertations / Theses: 'Magnetic transition'

1

Felton, Solveig. "Tunable Magnetic Properties of Transition Metal Compounds." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5939.

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2

Stanley, Daniel C. "MAGNETIC DAMPING IN FE3O4 THROUGH THE VERWEY TRANSITION FOR VARIABLE AG THICKNESSES." Miami University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=miami1376500586.

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3

Niyongabo, Prime. "Second-Order Phase Transition in Magnetic and non-Magnetic ZnO." Thesis, University of Pretoria, 2014. http://hdl.handle.net/2263/46050.

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4

Aus, Martin J. "Magnetic properties of nanocrystalline transition metals." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq38299.pdf.

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5

Avalos, Ovando Oscar Rodrigo. "Magnetic Interactions in Transition Metal Dichalcogenides." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540818398439166.

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6

Chilton, Nicholas Frederick. "Magnetic anisotropy of transition metal complexes." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/magnetic-anisotropy-of-transition-metal-complexes(64b34057-8a7a-44db-a89a-22a233fdefb5).html.

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The study of magnetic anisotropy in molecular systems permeates the physical sciences and finds application in areas as diverse as biomedical imaging and quantum information processing. The ability to understand and subsequently to design improved agents requires a detailed knowledge of their fundamental operation. This work outlines the background theory of the electronic structure of magnetic molecules and provides examples, for elements across the Periodic Table, of how it may be employed to aid in the understanding of magnetically anisotropic molecules. The magnetic anisotropies of a series of dimetallic NiII2 complexes and a RuIII2MnII triangle are determined through multi-frequency Electron Paramagnetic Resonance (EPR) spectroscopy and ab initio calculations. The magnetic anisotropy of the former is found to be on the same order of magnitude as the isotropic exchange interactions, while that of the latter is found to be caused by large antisymmetric exchange interactions involving the RuIII ions. An intuitive electrostatic strategy for the prediction of the magnetic anisotropy of DyIII complexes is presented, allowing facile determination of magnetic anisotropy for low symmetry molecules. Through the presentation of the first near-linear pseudo-two-coordinate 4f-block complex, a new family of DyIII complexes with unprecedented Single Molecule Magnet (SMM) properties is proposed. Design criteria for such species are elucidated and show that in general any two-coordinate complex of DyIII is an attractive synthetic target. The exchange interaction between two DyIII ions is directly measured with multi-frequency EPR spectroscopy, explaining the quenching of the slow magnetic relaxation in the pure species compared to the SMM properties of the diluted form. The interpretation of this complex system was achieved with supporting ab initio calculations.

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7

Muxworthy, Adrian R. "Stability of magnetic remanence in multidomain magnetite." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:bc70e665-4c54-4ab5-98fa-d43ccecd07a1.

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If a rock is to retain a geologically meaningful magnetic record of its history, it is essential that it contains magnetic minerals which are capable of carrying stable magnetic remanence. Of the natural occurring magnetic minerals, magnetite is the most important because of its abundance and strong magnetic signature. The stability, i.e., the resistance to demagnetisation or reorientation, of magnetic remanence is related to grain size; in smaller grains the magnetic moments align to have single domain (SD) structures, in larger grains complex magnetic patterns are formed (multidomain (MD)). “Classical” domain theory predicts that SD remanence is stable, whilst MD remanence is not. However experimental evidence has shown that both SD and MD grains can have stable remanences. In this thesis the origin of stable MD remanence is examined. There are two opposing theories; one suggests that the stability is due to independent SD-like structures, the other postulates that the stability is due to metastable MD structure. A series of experiments were designed to examine the stability using a selection of characterised synthetic and natural samples. Low-stress hydrothermal recrystallised samples where grown for this study. For the first time, the stability of thermoremanence induced in hydrothermal crystals to cooling was examined. The results agree with previous observations for crushed and natural magnetites, and support kinematic models. The behaviour of SIRM and thermoremanences in MD magnetite to low-temperature cooling to below the crystallographic Verwey transition at 120-124 K (T_v) and the cubic magnetocrystalline anisotropy isotropic point (T_k) at 130 K was investigated. On cooling through T_v, SIRM was observed to decrease and demagnetise, however thermoremanence was found to display a large increase in the magnetisation at T_v, which was partially re- versible on warming. The size of the anomaly is shown to be dependent on the temperature at which the thermoremanence is acquired, internal stress and grain size. The anomaly is attributed to the large increase in the magnetocrystalline anisotropy which occurs on cooling through T_v . It is postulated that low-temperature cycling demagnetisation is due to kinematic processes which occur on cooling between room temperature and T_k. Characterisation of low-temperature treated remanence and partially alternating field demagnetised remanence, suggest that the stable remanence is multidomain. Low-temperature cooling of remanence in single sub-micron crystals was simulated using micromagnetic models. The models predict the observed anomaly for thermoremanence on cooling through T_v, and also the relative behaviour of SIRM and thermoremanence. The single domain threshold was calculated for the low-temperature phase of magnetite, and was found to be 0.14 microns, compared to 0.07 microns at room temperature.

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8

Liu, Mingde. "Magnetization-steps spectroscopy in dilute magnetic semiconductors and in molecular magnetism /." Thesis, Connect to Dissertations & Theses @ Tufts University, 1998.

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Thesis (Ph.D.)--Tufts University, 1998 .
Adviser: Yaacov Shapira. Submitted to the Dept. of Physics. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;

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9

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.

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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 (Fe_1-xM_x)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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10

Lounis, Samir. "Theory of magnetic transition metal nanoclusters on surfaces." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=984500766.

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11

Mills, Gordon. "Structural and magnetic studies of transition metal alloys." Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238776.

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12

Lucas, Alun James. "Nuclear magnetic resonance studies of transition metal hydrides." Thesis, University of Warwick, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282531.

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13

Wang, Xiaobin. "Studies on dynamic thermal reversal and transition jitter in magnetic materials /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3099914.

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14

Xu, Ming. "Critical current density and time-dependent magnetization of the high transition temperature superconductors." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/30033.

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15

Bieringer, Mario. "Magnetic frustration in transition metal oxides with triangular, tetrahedral and square planar magnetic sublattices." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0029/NQ66253.pdf.

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16

Hargreaves, Joe. "The Verwey transition : neutron scattering studies of the vibrational and magnetic excitations in magnetite." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505388.

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The Verwey transition in magnetite is a remarkable and challenging phenomenon which is still not understood despite many years of intense research. When the temperature is lowered below the transition temperature (Tv = 121 K) there is a sudden drop in the electrical conductivity and the structure- changes from cubic above to monoclinic below. The importance of this phase transition goes further than just this simple material. Magnetite stands as a model system in many areas of the physical sciences, but is probably most known for its use in the theory of 'metal-insulator' transitions, that are known to occur in many of the transition metal oxides. For a long time it was thought that the mechanism responsible for this transition was ionic charge ordering of the iron atoms. This model has since been proven to be incorrect and new models with partial charge ordering have largely taken its place. This work is concerned with using the neutron as a probe to study both the vibrational and magnetic excitations within magnetite and offers insight into the lattice dynamics around the phase transition. The transverse acoustic phonons have been intensively studied and interesting broadening effects observed. Furthermore the entire spin wave spectrum has been observed, with the top mode (known as (1)2) and a direction other than [1 0 0] reported for the ftrst time. From the work presented here it is suggested that the structural phase transition in magnetite is better understood using a band type model where both phases of magnetite (above and below) are in fact semiconducting. The broadening effects of the phonons are described by the presence of an anharmonic potential above the transition temperature and the sudden drop in the electrical conductivity is explained by the widening of the band gap below the transition.

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17

Gök, Şafak. "Electrical and magnetic investigations on transition metal implanted GaAs." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983511020.

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18

Dube, Paul A. "Properties of magnetic transition metal-bromide graphite intercalation compounds /." *McMaster only, 2002.

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19

Ghosh, Sadhan. "Charge induced tunable magnetic properties in transition metal alloys." Karlsruhe : Forschungszentrum Karlsruhe, 2008. http://d-nb.info/989599701/34.

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20

Senn, Mark Stephen. "Charge, orbital and magnetic ordering in transition metal oxides." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7828.

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Neutron and x-ray diffraction has been used to study charge, orbital and magnetic ordering in some transition metal oxides. The long standing controversy regarding the nature of the ground state (Verwey structure) of the canonical charge ordered material magnetite (Fe3O4) has been resolved by x-ray single crystal diffraction studies on an almost single domain sample at 90 K. The Verwey structure is confirmed to have Cc symmetry with 56 unique sites in the asymmetric unit. Charge ordering is shown to be a useful first approximation to describe the nature of the ground state, and the conjecture that Verwey made in 1939 has finally been confirmed. However, three-site distortions which couple to the orbital ordering of the Fe2+ ordered states (trimerons) are shown to provide a more complete description of the low temperature structure. Trimerons explain the rather continuous distribution of the valence states observed in magnetite below Tv, anomalous shortening of Fe-Fe distances and the off-centre distortions resulting in ferroelectricity. DFT+U electronic structure calculations on the experimental coordinates support the conclusion of this crystallographic study, with the highest electron densities calculated for those Fe-Fe distances predicated to participate in the trimeron bonds. The 6H-perovskites of the type Ba3ARu2O9 have been reinvestigated by high resolution neutron and x-ray power diffraction. The charge ordered state of Ba3NaRu2O9 has been characterised at 110 K (P2/c, a =5.84001(2) Å, b = 10.22197(4) Å, c = 14.48497(6) Å, β = 90.2627(3) °) and shown to consist of a structure with near integer charge ordering of Ru5+ 2O9 / Ru6+ 2O9 dimers. The ground state has been shown to be very sensitive to external perturbations, with a novel melting of charge ordering observed under x-ray irradiation below 40 K (C2/c, a =5.84470(2) Å, b = 10.17706(3) Å, c = 14.45866(5) Å, β = 90.2151(3)-° at 10 K). High pressure studies reveal that the Ru-Ru intra-dimer distance may dictate the response of the system to pressure. Empirical trends in the Ba3ARu2O9 series of compounds have shown that change in ‘chemical pressure’ in these systems may be rationalised in terms of Coulomb’s law. In A = La and Y the magnetic ordering is shown to be FM within the Ru2O9 dimers (1.4(2) μB and 0.5(1) μB, respectively per Ru), representing the first case of intra dimer FM coupling reported in a system containing face-sharing RuO6 octahedra . The overall AFM coupling of the dimers implies an as yet unobserved breaking of the parent symmetry. In A = Nd, a complex competition between the crystal field effect of Nd3+ and the magnetic ordering of the Ru2O9 FM moments has been observed, leading first vi to FM order of Nd at 25 K (1.56(7) μB) followed by ordering of Ru moments (0.5(1) μB) and a spin reorientation transition of Nd moments at 18 K. In A = Ca, the formation of a singlet ground state is observed in Ru2O9 rather than the expected AFM coupling and below 100 K Ba3CaRu2O9 is diamagnetic. All five systems indicate that the Ru2O9 dimer is the physically significant unit in these systems when considering structural trends and the ordering of charge, spin and orbital degrees of freedom.

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21

Seo, Jiwon. "Electronic and magnetic properties of transition metal oxide heterostructures." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611390.

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22

Jassim, Ishmaeel Khalil. "Magnetic and lattice interaction in 3D transition metal compounds." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/31919.

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The importance and nature of magnetic and lattice degrees of freedom and their interaction in transition metal magnets has been investigated. Two different alloy systems in which the magnetic 3D electrons either had localised or itinerant characteristics were chosen. As an example of localised behaviour, Heusler alloys in which the magnetic moment was confined to Mn atoms were chosen, e.g. Pd2MnIn. The manganese atoms are separated by more than 4.6Å. These materials provide a good approximation to a Heisenberg system, having long-range interactions.

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23

Zhou, Shengqiang. "Transition metal implanted ZnO: a correlation between structure and magnetism." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1209998012687-36583.

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Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carriermediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.

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24

Tucker, Nigel Paul. "Magnetic structure of Gd thin-film surfaces." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364156.

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25

Zhou, Shengqiang. "Transition metal implanted ZnO: a correlation between structure and magnetism." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23718.

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Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carriermediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.

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26

Attfield, J. P. "The structural and magnetic properties of some transition metal compounds." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379913.

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27

Knee, Christopher Sebastian. "Synthesis, structure and magnetic properties of complex metal oxides." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299519.

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28

Lindley, E. J. "Neutron scattering studies of transition metal alloys." Thesis, University of Southampton, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355332.

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29

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.

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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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Stampe, Patricia A. "Superconducting, magnetic and transport properties of several transition metal systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23669.pdf.

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31

Wijngaard, Jan Hendrik. "Magnetic and magneto-optical properties of some transition metal compounds." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 1990. http://irs.ub.rug.nl/ppn/297971859.

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32

Warren, Paul. "Neutron scattering studies of materials near the magnetic phase transition." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6261/.

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Metals on the verge or just in the weakly magnetic state offer a unique testing ground for current theories of itinerant magnetism. Three investigations of such systems using neutron scattering are outlined in this work. TiBe(_2) is of interest since the random substitution of copperat Be atom sites expands the lattice allowing one to cross the threshold from an incipient to a weakly magnetic state. Small angle neutron scattering studies of spin density fluctuations in TiBe(_1.5) Cu(_0.5) have shown that a single phenomonological model is sufficient to describe the collected integrated intensities above and below the magnetic phase transition temperature. Observations below the transition temperature may be attributed to scattering from damped spin waves. Polarised neutron diffraction studies of a single crystal of ZrFe(_2) are in contradiction with reported band structure calculations of a strong ferrimagnetic ground state. The magnetic distribution in real space around the Fe ions is highly spherical and the form factor closely follows that of free Fe ions in reciprocal space. A small angle neutron scattering investigation of the helical spin wave density wave in MnSi below the magnetic phase transition and spin density fluctuations in the paramagnetic regime under hydrostatic pressure has been performed.

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33

Bingham, Stephen John. "Magnetic circular dichroism and electron paramagnetic resonance of transition ions." Thesis, University of East Anglia, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357179.

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34

Liu, Hui-Ping. "Magnetic ordering and crystal structure in selected transition-metal compounds /." Uppsala : Acta Universitatis Upsaliensis, 1999. http://catalogue.bnf.fr/ark:/12148/cb402057270.

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35

Papadopoulos, Konstantinos. "Investigation of magnetic order in nickel-5d transition metal systems." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-383009.

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Double perovskite materials exhibit alterations in magnetic order through manipulation oftheir crystal structure. Certain ultra thin metallic bilayers can create an exotic magnetic stateof confined spin textures called skyrmions. In both cases, new atomic arrangements leadto new electrical and magnetic properties. The following work comprises two studies, bothof which examine the magnetic properties of transition metals in either powder or thin filmsamples. The first part is dedicated to a series of muon spin rotation and relaxation (muSR)experiments on a LaSrNiReO6, double perovskite, powder sample. In the muSR technique, aspin polarized muon beam is focused onto a powder envelope in low pressure and temperatureconditions. The spins of the implanted muons evolve depending on the intrinsic or externallyapplied magnetic field according to Larmor precession. The measurement is based onthe detection of decay positrons that carry this precession information on their preferreddecay directions. Measurements that were realized in wTF, ZF and LF setups, reveal asecond transition to magnetic order at Tc ≃ 22K, below a transition that was observed at T =261K from magnetic susceptibility measurements. The experimental results point to threemagnetic phases, paramagnetic for T > 261K, dilute ferrimagnetic for 22 < T < 261K and amagnetically ordered state for T < 22K, that may implicate ferro- and antiferromagnetismfrom Ni sublattices and Ni-Re interactions. The second part follows an attempt to produce and characterize ultra thin bilayer filmsfor the observation of interfacial chiral structures and skyrmions. Co/Fe/MgO (100) andW/Ni/Cu (100) bilayers were grown with magnetron sputter deposition in various layerthicknesses and their structure was determined by X-ray reflectometry (XRR). The XRRscans presented a relatively thick-layered Co/Fe/MgO film, while extremely thin and roughW/Ni/Cu bilayers, for the purposes of studying films with broken interfacial inversionsymmetry. This study was concluded with indicative magneto-transport measurements thatalso point to the reconfiguration of the growth procedure.

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36

Mole, Richard Adam. "Investigation into the magnetic properties of transition metal hydroxy squarates." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614078.

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37

Lago, Jorge. "Magnetic ordering and dynamics of two transition metal oxide systems." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670216.

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38

Saureu, Artesona Sergi. "From mononuclear to dinuclear: magnetic properties of transition metal complexes." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/386451.

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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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39

Ranmohotti, Kulugammana G. S. "Synthesis, structure and magnetic properties of oxy-anion based magnetic solids containing transition metal oxide nanostructures." Connect to this title online, 2008. http://etd.lib.clemson.edu/documents/1233347528/.

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40

Bailey, Tony. "Studies of the magnetic properties and microstructures of two rare earth-transition metal type magnetic alloys." Thesis, University of Birmingham, 1985. http://etheses.bham.ac.uk//id/eprint/196/.

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An investigation into the optimisation of magnetic properties of two types of magnetic alloys based on Sm(Co,Cu,Fe,Zr)_z (z = 7.4) and Nd₁₅Fe₇₇B₈ has been carried out. The optimum heat treatment which gave the best magnetic properties for the Sm(Co,Cu,Fe,Zr)_z alloy depended primarily on the sintering and solid solution temperatures. After quenching the alloy from the solid solution temperature, and then ageing isothermally, it was found that the intrinsic coercivity, microhardness and electrical resistance changed with ageing time, and the ageing temperature also affected the rate of these changes. The magnetic properties of specimens produced from the Nd-Fe-B type alloy were also shown to be affected by different heat treatments. The microhardness, microstructure and intrinsic coercivity were affected by an isothermal ageing treatment and the temperature of the treatment. Two routes were used for powder preparation 1n the production of the sintered specimens: i. Mechanical ball milling of crushed ingot material. ii. Hydrogenation followed by ball milling. It was found that higher energy products were achieved in the ball milled material for the two alloys investigated. Two reasons for this were proposed: i. The hydrogenated and ball milled powder had a larger size than the ball milled only powder. ii. The surfaces of the hydrogenated powder were highly reactive in air and some oxidation of the surfaces occurred. Optical and electron microscope studies showed that the variations in the ageing behaviour of both the alloys was concurrent with subtle differences in the microstructure between the samples aged at different isothermal ageing temperatures.

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41

Aldous, David W. "The solvothermal synthesis of early transition metal fluorides." Thesis, University of St Andrews, 2008. http://hdl.handle.net/10023/578.

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In this thesis, 60 crystal structures which have been synthesised by the solvothermal method are reported, with 57 of them representing novel materials. The remaining three materials have previously been reported but have been made by a new and milder method of synthesis. Ti, Zr, Hf, V, Nb, Ta and Mo have all been used to make fluoride or oxyfluoride materials at temperatures ranging from 60C to 200C. Both inorganic and organic moieties ("templates") have been used to direct the formation of the (oxy)fluoride materials, usually as an anionic species. These materials have then been studied for their magnetic properties, where relevant. Initially, 10 vanadium-based compounds were made at 100C using a range of templates. Through variations in water content, temperature and cation ratio, a further 19 compounds were synthesised. The inorganic species in these structures ranged from monomers, to dimers, tetramers and chains, to infinite 2D sheets. A family of vanadium compounds has been synthesised, with piperazine as a template, which shows an increase in covalent connectivity through the increase of the reaction temperature, with a decrease in oxidation state as a result. These materials are also interrelated through the use of a "Y" shaped motif in their structural composition. Through a change in cation content a novel trigonal chain compound (related to the structure of CsCrF₄) has been synthesised with piperazine which possibly shows strong geometric frustration. Vanadium oxyfluoride analogues of (VO)₂P₂O₇ have been made, which show interesting magnetic properties with a range of different templates, ranging from alkali metal cations to the bulky protonated template trans 1,2 bis (4-pyridyl) ethene. The best fits to the magnetic susceptibility data are obtained with an antiferromagnetic Heisenberg chain model. Nine molybdenum-based structures have also been synthesised, with five of the structures being made through changes in the temperature and cation ratio of the reactions. An example of this is the formation of tetrameric units with ammonium, through the condensation of monomers as a result of an increase in the reaction temperature. A further 22 structures have also been made with metals, M = Ti, Zr, Hf, Nb and Ta. These structures have a tendency to form isolated polyhedral units under the conditions studied in this work. Several examples of isolated [MF₆][superscript n-] and [MF₇][superscript n-] monomers are reported and also one example of a trans-connected [TiOF₄]²⁻ infinite chain structure.

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Kummari, Venkata Chandra Sekhar. "A New Approach for Transition Metal Free Magnetic Sic: Defect Induced Magnetism After Self-ion Implantation." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc271849/.

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SiC has become an attractive wide bandgap semiconductor due to its unique physical and electronic properties and is widely used in high temperature, high frequency, high power and radiation resistant applications. SiC has been used as an alternative to Si in harsh environments such as in the oil industry, nuclear power systems, aeronautical, and space applications. SiC is also known for its polytypism and among them 3C-SiC, 4H-SiC and 6H-SiC are the most common polytypes used for research purposes. Among these polytypes 4H-SiC is gaining importance due to its easy commercial availability with a large bandgap of 3.26 eV at room temperature. Controlled creation of defects in materials is an approach to modify the electronic properties in a way that new functionality may result. SiC is a promising candidate for defect-induced magnetism on which spintronic devices could be developed. The defects considered are of room temperature stable vacancy types, eliminating the need for magnetic impurities, which easily diffuse at room temperature. Impurity free vacancy type defects can be created by implanting the host atoms of silicon or carbon. The implantation fluence determines the defect density, which is a critical parameter for defect induced magnetism. Therefore, we have studied the influence of low fluence low energy silicon and carbon implantation on the creation of defects in n-type 4H-SiC. The characterization of the defects in these implanted samples was performed using the techniques, RBS-channeling and Raman spectroscopy. We have also utilized these characterization techniques to analyze defects created in much deeper layers of the SiC due to implantation of high energy nitrogen ions. The experimentally determined depths of the Si damage peaks due to low energy (60 keV) Si and C ions with low fluences (< 1015 cm-2) are consistent with the SRIM-2011 simulations. From RBS-C Si sub-lattice measurements for different fluences (1.1×1014 cm-2 to 3.2×1014 cm-2) of Si implantation in 4H-SiC, the Si vacancy density is estimated to range from 1.29×1022 cm-3 to 4.57×1022 cm-2, corresponding to average vacancy distances of 4.26 Å to 2.79 Å at the damage peak (50±5 nm). Similarly, for C implanted fluences (1.85×1014 cm-2 to 1×1015 cm-2), the Si vacancy density varies from 1.37×1022 cm-3 to 4.22×1022 cm-3 with the average vacancy distances from 4.17 Å to 2.87 Å at the damage peak (110±10 nm). From the Raman spectroscopy, the implantation-induced lattice disorders calculated along the c-axis (LO mode) and perpendicular to c-axis (TO mode) in 4H-SiC are found to be similar. Furthermore, the results obtained from SQUID measurements in C implanted n-type 4H-SiC sample with fluences ranging from 1×1012 to 1.7×1016 ions/cm2 have been discussed. The implanted samples showed diamagnetism similar to the unimplanted sample. To date, to our best of knowledge, no experimental work has been reported on investigating defect induced magnetism for self-ion implantation in n-type 4H-SiC. These first reports of experimental results can provide useful information in future studies for a better understanding of self-ion implantation in SiC-based DMS.

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43

Beeck, Torben [Verfasser]. "Small, Size-Selected and Deposited Clusters on Magnetic and Non-Magnetic 3d Transition Metal Surfaces / Torben Beeck." München : Verlag Dr. Hut, 2015. http://d-nb.info/1074063503/34.

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44

Saleem, Muhammad. "Study of magnetic features of Nd₂Fe₁₄B through the spin reorientation transition by magnetic force microscopy." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/61353.

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Nd₂Fe₁₄B is one of the high performance permanent magnets that has appeared as an appealing compound for commercial applications. The understanding of its macroscopic magnetic properties through the study of its magnetic domain structures has received great attention. In this study, we use magnetic force microscopy (MFM) to image the magnetic features as a function of temperature through the spin-reorientation transition temperature (TSR ∼ 135 K) of a Nd₂Fe₁₄B single crystal. We observe a pronounced change in the anisotropy of the magnetic features upon cooling from 170 K to 100 K. Our autocorrelation analysis of the MFM images reveals an increase in the four-fold component of the anisotropy below TSR. The magnetic feature size is estimated from the two-fold and four-fold components and found to be between 4.5 µm and 6 µm below TSR. We observe an average magnetic feature size around 5 µm above the spin reorientation transition. The complexity in the geometry of magnetic features is studied from the fractal dimension (FD) analysis. Higher values of FD below TSR indicate that the magnetic features possess more rugged boundaries. Average values of FD increase from 1.17 ± 0.05 for T > TSR to 1.29 ± 0.04 for T < TSR.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

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45

Cairns, Melissa Ann. "Weak Anchoring Effects on Magnetic Field Induced Transitions of a Cholesteric Liquid Crystal Filmwith Negative Magnetic Anisotropy." Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1563550315014445.

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46

Ghosh, Sadhan [Verfasser]. "Charge induced tunable magnetic properties in transition metal alloys / Sadhan Ghosh." Karlsruhe : Forschungszentrum Karlsruhe, 2008. http://d-nb.info/989599701/34.

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47

Krätschmer, Wolfgang [Verfasser]. "Nuclear Magnetic Resonance in Strongly Correlated Transition–Metal Oxides / Wolfgang Krätschmer." München : Verlag Dr. Hut, 2014. http://d-nb.info/1047037092/34.

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48

Tabookht, Zahra. "Theoretical study of magnetic and conducting properties of transition metal nanowires." Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/52798.

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En la presente tesis doctoral se ha realizado un estudio computacional de las propiedades electrónicas de sistemas basados en cadenas metálicas monodimensionales de la familia de los llamados nanowires, concretamente su magnetismo y conductividad. Estas cadenas lineales se sustentan gracias a los ligandos orgánicos que se organizan a su alrededor, cuyo número de sitios de unión determina la nuclearidad de la cadena. Para estas moléculas, llamadas cadenas metálicas extendidas, se han calculado los parámetros de acoplamiento magnético con el método CASPT2. El uso del Hamiltoniano de Heisenberg estándar para los sistemas M3(dpa)4Cl2 cuando hay dos electrones no desapareados en cada centro, ha sido examinado mediante el cálculo del valor de λ mediante cálculos DFT. Las diferentes conductividades eléctricas observadas en las cadenas MMX [Ni2(dta)4I]∞ y [Pt2(dta)4I]∞ (dta = CH3CS2) y sus estados de ordenación de carga han sido analizados con parámetros de estructura electrónica extraídos a partir de cálculos DFT periódicos y de correlación combinados con la teoría del Hamiltoniano efectivo.
In the present thesis, magnetic and conducting properties of systems, one-dimensional chains of the family of so-called nanowires, have been studied computationally. These linear chains are supported by organic ligands surrounding the metal backbone where the number of binding sites determines the nuclearity of the chain. For these molecules, also called extended metal atom chains, magnetic coupling parameters have been calculated with the CASPT2 method. The use of standard Heisenberg Hamiltonian for systems M3(dpa)4Cl2 when two unpaired electrons are localized on each magnetic center has been examined by calculating the value of λ from DFT calculations. The different electrical conductivities observed in MMX chains [Ni2(dta)4I]∞ and [Pt2(dta)4I]∞ (dta = CH3CS2) and the charge ordering state have been analyzed with DFT periodic calculations and also through the comparison of extracted electronic structure parameters from ab initio calculations combined with the effective Hamiltonian theory.

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Sullivan, Matthew C. "The normal-superconducting phase transition of YBCO in zero magnetic field." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/226.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Košuth, Michal. "Magnetic properties of transition metal surfaces and GaAs-Fe heterogeneous systems." Berlin Logos, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=3049391&prov=M&dok_var=1&dok_ext=htm.

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Dissertations / Theses on the topic 'Magnetic transition'

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