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1
Yokoyama, Koji. "Muon probes of spin-polarized electrons in GaAs". Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=104&did=1907186881&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270484411&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Includes bibliographical references (leaves 121-123). Issued in print and online. Available via ProQuest Digital Dissertations.
2
Kuwahara, M., T. Morino, T. Nakanishi, S. Okumi, M. Yamamoto, M. Miyamoto, N. Yamamoto i in. "Spin-Polarized Electrons Extracted from GaAs Tips using Field Emission". American Institite of Physics, 2007. http://hdl.handle.net/2237/11993.
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Löffler, Wolfgang. "Electrical preparation of spin-polarized electrons in semiconductor quantum dots". [S.l. : s.n.], 2008. http://digbib.ubka.uni-karlsruhe.de/volltexte/1000008367.
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Went, Michael Ray, i n/a. "Scattering of Spin Polarized Electrons from Heavy Atoms: Krypton and Rubidium". Griffith University. School of Science, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040220.134142.
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This thesis presents a set of measurements of spin asymmetries from the heavy atoms krypton and rubidium. These investigations allow examination of the spin orbit interaction for electron scattering from the target atoms. These measurements utilise spin polarized electrons in a crossed beam experiment to measure the Sherman function from krypton and the A2 parameter from the 52P state of rubidium. The measurements utilise a new spin polarized electron energy spectrometer which is designed to operate in the 20-200 eV range. The apparatus consists of a standard gallium arsenide polarized electron source, a 180 degrees hemispherical electron analyser to detect scattered electrons and a Mott detector to measure electron polarization. A series of measurements of the elastic Sherman function were performed on krypton at incident electron energies of 20, 50, 60, 65, 100, 150 and 200 eV. Scattered electrons are measured over an angular range of 30-130 degrees. These measurements are compared with calculations of the Sherman function which are obtained by solution of the Dirac-Fock equations. These calculations include potentials to account for dynamic polarization and loss of flux into inelastic channels. At the energies 50, 60 and 65 eV, experimental agreement with theory is seen to be extremely dependent on the theoretical model used. Measurement of the A2 parameter from the combined 52P1/2,3/2 state of rubidium are performed at an incident energy of 20 eV. The scattered electrons are measured over an angular range of 30-110 degrees. This measurement represents the first such measurement of this parameter for rubidium. Agreement with preliminary calculations performed using the R-matrix technique are good and are expected to improve with further theoretical development.
5
Went, Michael Ray. "Scattering of Spin Polarized Electrons from Heavy Atoms: Krypton and Rubidium". Thesis, Griffith University, 2003. http://hdl.handle.net/10072/365606.
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This thesis presents a set of measurements of spin asymmetries from the heavy atoms krypton and rubidium. These investigations allow examination of the spin orbit interaction for electron scattering from the target atoms. These measurements utilise spin polarized electrons in a crossed beam experiment to measure the Sherman function from krypton and the A2 parameter from the 52P state of rubidium. The measurements utilise a new spin polarized electron energy spectrometer which is designed to operate in the 20-200 eV range. The apparatus consists of a standard gallium arsenide polarized electron source, a 180 degrees hemispherical electron analyser to detect scattered electrons and a Mott detector to measure electron polarization. A series of measurements of the elastic Sherman function were performed on krypton at incident electron energies of 20, 50, 60, 65, 100, 150 and 200 eV. Scattered electrons are measured over an angular range of 30-130 degrees. These measurements are compared with calculations of the Sherman function which are obtained by solution of the Dirac-Fock equations. These calculations include potentials to account for dynamic polarization and loss of flux into inelastic channels. At the energies 50, 60 and 65 eV, experimental agreement with theory is seen to be extremely dependent on the theoretical model used. Measurement of the A2 parameter from the combined 52P1/2,3/2 state of rubidium are performed at an incident energy of 20 eV. The scattered electrons are measured over an angular range of 30-110 degrees. This measurement represents the first such measurement of this parameter for rubidium. Agreement with preliminary calculations performed using the R-matrix technique are good and are expected to improve with further theoretical development.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Science
Full Text
6
Hansen, Jens-Ole 1965. "A measurement of spin-dependent asymmetries in quasielastic scattering of polarized electrons from polarized helium-3". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32634.
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Taborelli, Mauro. "Magnetism of epitaxial thin films and single-crystal surfaces studied with spin-polarized secondary electrons /". [S.l.] : [s.n.], 1988. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=8545.
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Nakamura, Katsuro. "Longitudinal Double-Spin Asymmetry of Electrons from Heavy Flavor Decays in Polarized p+p Collisions at √s =200 GeV". 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/175120.
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Allen, William D. "Aspects of spin polarised transport". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368082.
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Gröbli, Jean-Claude. "Spin filter and highly polarized electron sources /". [S.l.] : [s.n.], 1995. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=11148.
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Hatton, D. C. "Spin polarized electron scattering at ferromagnetic interfaces". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603854.
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Sadeghzadeh, Kayvan. "Spin polarised Fermi gases". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610744.
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Allenspach, Rolf Allenspach Rolf Allenspach Rolf Allenspach Rolf. "Magnetic characterization at surfaces by spin polarized electron spectroscopies /". [S.l.] : [s.n.], 1985. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=7952.
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Buckle, S. J. "Molecular field effects in electron spin polarized atomic deuterium". Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372071.
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Mohamad, Haidar Jawad. "Ultrafast optical measurements of spin-polarized electron dynamics in nanostructured magnetic materials". Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18425.
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At present, electronic devices depend upon electric charge to transfer and record information. However, such devices are approaching a scaling limit due to Joule heating. Spintronics offers a solution by exploiting the spin rather than the charge of the electron, since the propagation of spin current can in principle occur without dissipation. Immediate applications lie in magnetic random access memory and novel media for hard disk recording. Within this thesis, the Magneto-optical Kerr effect (MOKE) has been used to measure the static and dynamic magnetic properties of a number of different thin film samples that are of interest for spintronic applications. A femtosecond laser has been used to perform time-resolved MOKE (TRMOKE) and time resolved reflectivity (TRR) measurements simultaneously, which probe the spin and charge dynamics respectively. Measurements have been performed upon a continuous thin film of CrO2 that is known to be half-metallic in bulk form, and a series of YIG/Cu/Ni81Fe19 based structures that are expected to exhibit the spin Seebeck effect (SSE). Chemical vapour deposition (CVD) was used to fabricate the continuous CrO2 thin film on a (100)-oriented TiO2 substrate. Precessional magnetisation dynamics were studied by means of the TRMOKE technique. The dependence of the precession frequency and the effective damping parameter upon the static applied magnetic field were investigated. The precession frequency exhibited a minimum at the hard axis saturation field as expected. However precession was also observed for fields greater than the hard axis saturation value, perhaps suggesting the presence of a twisted magnetic state within the film. TRMOKE and TRR measurements were performed upon the YIG/Cu/Ni81Fe19 based structures for different values of the pump fluence and applied magnetic field. For fixed pump fluence and varying applied field, the frequency of precession is well described by a numerical solution of the Landau-Lifshitz equation for the Ni81Fe19 (permalloy, Py) layer. The frequency, amplitude, damping, phase and chirp of the precessional oscillations was extracted from measurements made with a field of 3 kOe applied at 2.8° from the normal to the sample plane, in a configuration designed to maximise any spin transfer torque (STT) generated by the SSE. The oscillation parameters extracted for trilayer samples and a Py reference sample were found to be very similar. Features indicative of STT predicted by simulations were not observed. This suggests that either the YIG/Cu interface was unable to efficiently transmit spin current within the samples studied here, or else that the STT generated by means of the SSE is too small to be of practical use.
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Okumi, Shoji, Naoto Yamamoto, Kuniaki Tamagaki, Atsushi Mano, Ryosuke Sakai, Masahiro Yamamoto, Makoto Kuwahara i in. "Development of the New Type Polarized Electron Source for SPLEEM". American Institite of Physics, 2007. http://hdl.handle.net/2237/11990.
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Kato, Takashi, Yasuhito Ishikawa, Hiroyoshi Itoh i Jun-ichiro Inoue. "Intrinsic anisotropic magnetoresistance in spin-polarized two-dimensional electron gas with Rashba spin-orbit interaction". American Physical Society, 2008. http://hdl.handle.net/2237/11252.
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Pramanik, Sandipan. "Spin Polarized Transport in Nanoscale Devices". VCU Scholars Compass, 2006. http://scholarscompass.vcu.edu/etd/1092.
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The ultimate goal in the rapidly burgeoning field of spintronics is to realize semiconductor-based devices that utilize the spin degree of freedom of a single charge carrier (electron or hole) or an ensemble of such carriers to achieve novel and/or enhanced device functionalities such as spin based light emitting devices, spin transistors and femto-Tesla magnetic field sensors. These devices share a common feature: they all rely on controlled transport of spins in semiconductors. A prototypical spintronic device has a transistor-like configuration in which a semiconducting channel is sandwiched between two contacts (source and drain) with a gate electrode sitting on top of the channel. Unlike conventional charge-based transistors, the source electrode of a spin transistor is a ferromagnetic (or half-metallic) material which injects spin polarized electrons in the channel. During transit, the spin polarizations of the electrons are controllably rotated by a gate electric field mediated spin-orbit coupling effect. The drain contact is ferromagnetic (or half-metallic) as well and the transmission probability of an electron through this drain electrode depends on the relative orientation of electron spin polarization and the (fixed) magnetization of the drain. When the spins of the electrons are parallel to the drain magnetization, they are transmitted by the drain resulting in a large device current (ON state of spin FET). However, these electrons will be completely blocked if their spins are antiparallel to the drain magnetization, and ideally, in this situation device current will be zero (OFF state of spinFET). Thus, if we vary the gate voltage, we can modulate the channel current by controlling the spin orientations of the electrons with respect to the drain magnetization. This is how transistor action is realized (Datta-Das model). However, during transport, electrons' velocities change randomly with time due to scattering and hence different electrons experience different spin-orbit magnetic fields. As a result, even though all electrons start their journey with identical spin orientations, soon after injection spins of different electrons point along different directions in space. This randomization of initial spin polarization is referred to as spin relaxation and this is detrimental to the spintronic devices. In particular, for Datta-Das transistor, this will lead to inefficient gate control and large leakage current in the OFF state of the spinFET. The aim of this work is to understand various spin relaxation processes that are operative in semiconductor nanostructures and to indicate possible ways of minimizing them. The theoretical aspect of this work (Chapters 2-5) focuses on the D'yakonov-Perel' process of spin relaxation in a semiconductor quantum wire. This process of spin relaxation occurs because during transport electron spin precesses like a spinning top about the spin-orbit magnetic field. We show that the conventional drift-diffusion model of spin transport, which has been used extensively in literature, completely breaks down in case of a quantum confined system (e.g. a quantum wire). Our approach employs a semi-classical model which couples the spin density matrix evolution with the Boltzmann transport equation. Using this model we have thoroughly studied spin relaxation in a semiconductor quantum wire and identified several inconsistencies of the drift-diffusion formalism.The experimental side of this work (Chapters 6-8) deals with two different issues: (a) performing spin transport experiments in order to extract spin relaxation length and time in various materials (e.g. Cu, Alq3) under one-dimensional confinement, and (b) measurement of the ensemble spin dephasing time in self-assembled cadmium sulfide quantum dots using electron spin resonance technique. The spin transport experiment, as described in Chapter 7 of this dissertation, shows that the spin relaxation time in organic semiconductor (Alq3) is extremely long, approaching a few seconds at low temperatures. Alq3 is the chemical formula of tris- 8 hydroxy-quinoline aluminum, which is a small molecular weight organic semiconductor. This material is extensively used in organic display industry as the electron transport and emission layer in green organic light emitting diodes. The long spin relaxation time in Alq3 makes it an ideal platform for spintronics. This also indicates that it may be possible to realize spin based organic light emitting diodes which will have much higher internal quantum efficiency than their conventional non-spin counterparts. From spin transport experiments mentioned above we have also identified Elliott-Yafet mode as the dominant spin relaxation mechanism operative in organic semiconductors. Electron spin resonance experiment performed on self-assembled quantum dots (Chapter 8) allows us to determine the ensemble spin dephasing time (or transverse spin relaxation time) of electrons confined in these systems. In quantum dots electrons are strongly localized in space. Surprisingly, the ensemble spin dephasing time shows an increasing trend as we increase temperature. The most likely explanation for this phenomenon is that spin dephasing in quantum dots (unlike quantum wells and wires) is dominated by nuclear hyperfine interaction, which weakens progressively with temperature. We hope that our work, which elaborates on all of the above mentioned topics in great detail, will be a significant contribution towards the current state of knowledge of subtle spin-based issues operative in nanoscale device structures, and will ultimately lead to realization of novel nano-spintronic devices.
19
Bebb, Andrew M. "Synchrotron radiation studies of spin-polarised electron momentum density distributions". Thesis, University of Warwick, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404845.
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Djeghloul, Fatima Zohra. "Study of organic semiconductor / ferromagnet interfaces by spin-polarized electron scattering and photoemission". Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-01062352.
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I studied organic semiconductor/ferromagnet interfaces by characterizing them by spin-polarized electron scattering and photoemission spectroscopy experiments. In the first part, a completely unexpected behaviour of the spin-dependent electron reflection properties of these interfaces is observed. In fact, sub-monolayer coverage of the organic molecules makes the electron reflection amplitude independent of the spin, i.e. both the reflectivity and the reflection phase become independent of the spin orientation of the incident electrons. Although I am not able at the moment to identify the cause of this phenomenon, I show that it is a very general phenomenon which is independent of the energy of the primary electrons, the choice of the ferromagnetic substrate, the choice of the organic molecule, and of the orientation of the initial spin polarization. It is not due to a change of the surface magnetization, a depolarization of the primary electrons, or a direct interaction of the molecules with the ferromagnetic substrate. Moreover, theory does not predict so far the experimental results and further research is required to unveil the physics behind these observations. In the second part of my thesis, spin-resolved photoemission experiments have been performed at the synchrotron SOLEIL. The main result is the observation of a highly spin-polarized molecule-induced electronic state close to the Fermi level. Measurements as a function of the organic layer thickness allow us to determine the interfacial character of this electronic state. Finally, these results are compared with theoretical calculations performed at the institute.
21
Pravica, Luka. "Polarised electron studies of spin-dependent interactions in zinc and krypton atoms". University of Western Australia. School of Physics, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0063.
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[Truncated abstract.] An apparatus has been built, tested and characterised with greatly increased precision and accuracy to enable spin-polarised electron impact explorations of angular momentum effects in atoms. A combination of experimental, computational and interpretative studies has revealed new phenomena. In zinc the polarisation of the radiated photons from excited and ionised-with-excited atoms was measured in terms of integrated Stokes parameters (P1, P2 and P3) and related to electron exchange and spin-orbit interaction using normalised state multipoles.
22
Schofield, Debra Mary. "Development of spin-polarised scanning tunnelling microscopy for the study of spin electronic materials". Thesis, University of York, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442379.
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Dörr, Kathrin. "Ferromagnetic manganites: spin-polarized conduction and competing interactions". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1193676987929-14995.
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Electronic properties of solids are vitally important for modern technology, one may think of microelectronics, magnetic data storage, communication technologies and others. Sometimes, it seems possible to postpone the step of fundamental understanding when starting the application of a new material. However, lasting success and discovery of principally new approaches is based on it ...
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Lindebaum, Stephan [Verfasser], Jürgen [Akademischer Betreuer] König i Wolfgang [Akademischer Betreuer] Belzig. "Spin-Polarized Transport in Single-Electron Spin-Valve Transistors / Stephan Lindebaum. Gutachter: Wolfgang Belzig. Betreuer: Jürgen König". Duisburg, 2012. http://d-nb.info/1036115887/34.
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Dörr, Kathrin. "Ferromagnetic manganites: spin-polarized conduction and competing interactions". Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A23959.
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Electronic properties of solids are vitally important for modern technology, one may think of microelectronics, magnetic data storage, communication technologies and others. Sometimes, it seems possible to postpone the step of fundamental understanding when starting the application of a new material. However, lasting success and discovery of principally new approaches is based on it ...
26
Zhou, Haosheng. "Theory of the magnetic resonance spectrum of spin-polarized hydrogen gas". Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26678.
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The Green's function method is applied to investigate the magnetic spin resonance spectra of three-dimensional and two-dimensional spin-polarized quantum gases.
The Hartree-Fock approximation is employed to calculate the one-particle Green's function of the atoms, then this one-particle Green's function is used for the calculation of the vertex part of the Green's function. Such a combination yields a self-consistent result. The absorption spectra are obtained from the calculation of the susceptibility in terms of the two-particle Green's function (bubble diagram). Some general expressions for the dispersion relation, for the effective mass of a spin wave, and for the dipolar frequency shift are given in the calculation.
In order to estimate the shift of the electron-spin-resonance (ESR) frequency, the effective dipole-dipole interactions among the hydrogen atoms are included in the calculation. These effective interactions are deduced from the ladder approximation, and hence are characterized by the scattering amplitude. The scattering amplitude is calculated numerically. The result shows that the theoretical value of the shift is smaller than the experimentally observed value by about 35%.Science, Faculty of
Physics and Astronomy, Department of
Graduate
27
Allsworth, Max Daniel. "The effect of spin-polarised electrons on superconductivity in a ferromagnet superconductor bilayer". Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273991.
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Phillips, Lee Charles. "Spintronic devices with highly spin-polarised manganite electrodes and graphene channels". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610490.
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Haidar, Mohammad. "Role of surfaces in magnetization dynamics and spin polarized transport : a spin wave study". Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00869643.
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In this thesis, the interplay between electron transport and magnetization dynamics is explored in order to access to fundamental properties of ferromag- netic metal thin films. With the aim of extracting the influence of the electron surface scattering on the spin-dependent resistivities, thickness series of permal-loy (Ni80Fe20) films were grown and studied. In addition to standard electrical and magnetic measurements, a detailed study of the propagation of spin waves along these films was performed. Resorting to the current-induced spin-wave Doppler shift technique, the degree of spin-polarization of the electrical current was extracted. This degree of spin-polarization was found to decrease when the film thickness decreases, which suggests that the film surfaces contribute to the spin dependent resistivities and tend to depolarize the electrical current.
30
Inoue, Jun-ichiro, Takashi Kato, Yasuhito Ishikawa i Hiroyoshi Itoh. "Vertex Corrections to the Anomalous Hall Effect in Spin-Polarized Two-Dimensional Electron Gases with a Rashba Spin-Orbit Interaction". The American Physical Society, 2006. http://hdl.handle.net/2237/7131.
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Seemann, Klaus Michael. "Spin polarized electron transport and the anomalous Hall effect in L10-ordered epitaxial Fe-alloys". Thesis, University of Leeds, 2009. http://etheses.whiterose.ac.uk/115/.
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Two epitaxial ferromagnets FePd and its isoelectronic partner FePt, which order in the well known face-centered tetragonal L10-phase, have been fabricated to (a) evaluate the current spin polarization in the ballistic and in the diffusive electron transport regime, (b) to elucidate whether there is a discrepancy in the current spin polarizations depending on the transport regime, how high this discrepancy is, and finally (c) how the spin-orbit scattering strength changes by replacing Pd by Pt. These are questions of fundamental importance in the field of electron transport studies in magnetic materials, in the recent years known as spintronics. The study began with experimental investigations on the structural, magnetic, and electron transport properties of a L10-ordered epitaxial iron-platinum (FePt) alloy layer fabricated by magnetron-sputtering on a single-crystal MgO(001) substrate. At all temperatures ranging from 2 K to 258 K, a diffusive spin current polarization of > 80% was found. To study the ballistic transport regime, point-contact Andreev-reflection measurements at 4.2 K were performed and a value for the ballistic current spin polarization of ∼ 42% was obtained (which compares very well with that of a polycrystalline thin film of elemental Fe). This discrepancy is attributed to a difference in the characteristic scattering times for oppositely spin-polarized electrons, such scattering times influencing the diffusive but not the ballistic current spin polarization. One of the main parameters in the L10-phase ferromagnets is the degree of crystallographic long range ordering. To investigate the influence of the long range ordering on the current spin-polarization, epitaxial FePd magnetic thin films of varying degrees of L10-phase chemical order were used. By quantitatively accounting for changes in micromagnetism through simulation and magnetic force microscopy, it is shown within the Levy-Zhang spin-mistracking theory of domain wall resistance, that this is connected to a change in the average degree of spin-dependence at the scattering centers that control the diffusive transport in this system, suggesting a possible means of producing highly spin-polarized currents in the diffusive electron transport regime. Finally, both materials L10-FePd and -FePt were investigated with respect to the anomalous Hall effect as a consequence of spin-orbit scattering. A linear dependence between transverse and longitudinal resistivity in epitaxial L10- ordered FePd and FePt films due to the anomalous Hall effect (AHE) has been observed. In ordered ferromagnets such a linear relation may be anticipated due to the skew-scattering mechanism; the absence of an additional quadratic term suggests that side-jump scattering, which is dominant in less well ordered material, has been effectively suppressed. One finds that on exchanging Pd for the heavier, though isoelectronic Pt, the skew-scattering deflection angle in an individual electronic scattering event dramatically increases from 17 to 49 mrad. This increase corresponds well to a Z3/2 dependence of the atomic spin-orbit interaction energy, contrary to commonly assumed Z4 dependence.
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Junior, Jaime Duarte. "Método autoconsistente de primeiros princípios spin polarizado de espaço direto". Universidade de São Paulo, 1991. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-08112013-154808/.
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Neste trabalho, apresentamos um metodo baseado no formalismo lmto-asa (combinacao linear de orbitais muffin-tin na aproximacao de esfera atomica) e no metodo de recorrencia, que possibilita calculos autoconsistentes de primeiros principios com polarizacao de spin no espaco direto. Para testar o metodo, calculamos a estrutura eletronica dos sistemas FENI IND.5 (ferromagnetico) e FEMN (antiferromagnetico). Os resultados mostraram boa concordancia com os obtidos por outros metodos. A fim de ilustrar o metodo aplicado a um sistema nao-periodico, calculamos a estrutura eletronica e a distribuicao local de momentos magneticos para um sistema constituido de uma impureza substitucional de FE numa matriz CU. Nossos resultados para momento magnetico e densidade de estados local para o sitio de impureza, concordam bem com resultados via metodo kkr-funcao de gren e experimentais, da literatura. O metodo aqui descrito e bastante flexivel e e muito util na obtencao de momentos magneticos locais em sistemas complexosIn this work we present an approach based on the linear muffin-tin orbital (LMTO) formalism in the atomic sphere approximation (ASA) and on the recursion method which allows us to perform first principies calculations in real space. To test the method, we obtain the electronic structure of ferromagnetic FeNi3 e antiferromagnetic FeMn. The results compare well with those obtained by others methods. To illustrate the scheme applied to a non-periodic system, we calculate the electronic structure and local magnetic moments for a substitutional impurity of Fe in a Cu host. Our results for the magnetic moment and local density of states at the Fe site, agree well with KKR-Green functions and experimental results in the literature. The scheme described here is extremely flexible and is very useful to obtain local distribuition of magnetic moments in complex metallic systems.
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Choi, Deung jang. "Kondo effect and detection of a spin-polarized current in a quantum point contact". Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE029/document.
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L'effet Kondo observé dans des objets individuels constitue un système modèle pour l’étude de corrélations électroniques. Ces dernières jouent un rôle moteur dans le domaine émergent de l'électronique de spin (ou spintronique) où l’utilisation d’atomes issus des terres rares et des métaux de transition est incontournable. Dans ce contexte, l’étude de l'interaction d’une impureté Kondo avec des électrodes ferromagnétiques ou avec d’autres impuretés magnétiques peut donc s’avérer fondamental pour la spintronique. L’effet Kondo est sensible à son environnement magnétique car en présence d’interactions magnétiques la résonance ASK se dédouble. Dans une certaine mesure, la résonance ASK agit comme un niveau atomique discret doublement dégénérée qui subit un dédoublement Zeeman en présence d'un champ magnétique ou plus généralement d’un champ magnétique effectif. Inversement, la détection d'un dédoublement Zeeman indique l'existence d'un champ magnétique. Dans une boîte quantique, le couplage de la boîte avec les deux électrodes est faible en général et la largeur de la résonance ASK est donc de l'ordre de quelques meV. Beaucoup d’études de l’effet Kondo en présence d’interactions magnétiques ont été menées sur les boîtes quantiques, grâce notamment au contrôle qui peut être exercé sur la résonance ASK, mais aussi grâce au faible élargissement de la résonance qui peut alors être dédoublée avec un champ magnétique de l’ordre de 10 Tesla ou moins. A ces études, s’ajoutent de nombreux travaux similaires menés avec des dispositifs tels des jonctions cassées comprenant une molécule individuelle jouant le rôle de l’impureté magnétique. En revanche, peu d’études de ce type ont été consacrées aux atomes individuels. Cela est dû à l’hybridation plus marquée entre l'impureté atomique et la surface comparée aux boîtes quantiques, qui entraine une largeur typique de 10 meV ou plus pour la résonance ASK. Un champ magnétique d'environ 100 T ou plus est alors nécessaire afin de dédoubler la résonance et donc en pratique difficile à mettre en oeuvre. Cette thèse est consacrée précisément à l’étude de l'interaction entre une impureté Kondo individuel et son environnement magnétique à l’aide d’un STM. Une nouvelle stratégie est adoptée ici par rapport aux études antérieures de ce genre. Tout d'abord, nous éliminons la barrière tunnel en établissons un contact pointe-atome. Nous formons ainsi un point de contact quantique comprenant une seule impureté Kondo. Deuxièmement, nous utilisons des pointes ferromagnétiques. Le contact pointe-atome permet de sonder l'influence du ferromagnétisme sur l'impureté Kondo vial’observation de la résonance ASK. La géométrie de contact permet tout particulièrement de produire une densité de courant polarisé en spin suffisamment élevée pour qu’elle entraîne un dédoublement de la résonance ASK. Ce dédoublement constitue la première observation à l’échelle atomique d’un phénomène connu sous le nom d’accumulation de spin, laquelle se trouve être une propriété fondamentale de la spintroniqueThe Kondo effect of these single objects represents a model system to study electron correlations, which are nowadays of importance in relation to the emerging field of spin electronics, also known as spintronics, where chemical elements with partially filled d or f shells play a central role. Also of particular interest to spintronics is the interaction of single Kondo impurities with ferromagnetic leads or with other magnetic impurities. A Kondo impurity is in fact sensitive to its magnetic environment as the ASK resonance is usually split into two resonances in the presence of magnetic interactions. To some extent, the ASK resonance acts as a two-fold degenerate energy level of an atom which undergoes a Zeeman splitting in the presence of an effective magnetic field. Conversely, the detection of a Zeeman splitting indicates the existence of a magnetic field. In a QD, the coupling of the QD to the two leads is very weak in general, and the Kondo resonance is in the range of a few meV. Many studies focusing on magnetic interaction have been carried out on QDs, due to the high control that can be extended to the ASK resonance and its low energy range, allowing to split the resonance with a magnetic field of 10 T. Similar work has also been carried out in single-molecule or lithographically-defined devices. Although STM is an ideal tool to study the Kondo effect of single atoms, there is still a strong lack of experimental studies concerning atoms in the presence of magnetic interactions. This is partly due to the stronger impurity-metal hybridization compared to QDs, which places the ASK width in the range of 10 meV. An effective magnetic field of 100 T would be needed to split the resonance. The present Thesis is devoted precisely at studying the interaction between a single Kondo impurity with its magnetic environment through STM. A new strategy is adopted herecompared to former studies of this kind. Firstly, we contact a single-magnetic atom on a surface with a STM tip thereby eliminating the vacuum barrier. Secondly, we use ferromagnetic tips. The contact with a single atom allows probing the influence of ferromagnetism on the Kondo impurity i. e. its ASK resonance. But most importantly, the contact geometry produces sufficiently high current densities compared to the tunneling regime, so that the ASK resonance becomes sensitive to the presence of a spin-polarized current. This constitutes the first atomic scale detection of a spin-polarized current with a single Kondo impurity
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Bowles, Cameron Michael Albert, i cameronbowles@hotmail com. "Pushing the boundaries of condensed matter electron momentum spectroscopy". The Australian National University. Research School of Physical Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20080409.193948.
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An electron momentum spectrometer at the Australian National University has been used to study various aspects of different solid state systems. EMS is a transmission mode technique and involves the collision of the incident electron with a bound electron, after which both electrons are ejected and measured in coincidence. Through well defined reaction kinematics the complete valence
spectral momentum density A(ɛ,q) can be measured. The spectrometer has been used to measure the spectral momentum
densities (spectral functions) of single crystal targets, as well as targets in disordered states. A new spin polarised electron source was constructed and implemented in the ANU spectrometer, which was used to measure spin dependent features of ferromagnetic samples.¶
This thesis is divided into seven chapters, the first chapter is an introduction into the field of electron momentum spectroscopy, highlighting what has been measured before and how the technique has progressed to its present state. Some comparisons to other experimental techniques will be made.¶
The second chapter describes the ANU EMS spectrometer in detail. The technique requires some technical and advanced equipment that is often used in novel ways. The production of thin (20 nm) free standing targets will be detailed, along with the experimental chamber and electronics used to run the apparatus and collect data. The determination of the energy and momentum resolution of the experiment is also described.¶
The third chapter will detail the design and construction of the new spin polarised electron source. The results of commissioning and characterizing the new source will be presented.¶
Chapters four through six will present the measured results. The fourth chapter will detail the single crystalline measurements for the group eleven noble metals (Cu, Ag and Au). Each sample was measured along three high symmetry directions and compared to a DFT calculation using the LDA and a FP-LMTO basis. The fifth chapter will include the results from samples that were in disordered states, a measurement which is unique to the EMS technique. The polycrystalline and amorphous states of the Si and Ge semiconductors are presented and conclusions are made to the degree of difference in the results and to which theoretical approach to the unique amorphous state of the semiconductors best matches the EMS results. The sixth chapter includes results of ferromagnetic iron, measured using the spin polarised electron source. The spectrometer was used to measure spin-polarised electron-energy-loss-spectroscopy (SPEELS) and magnetic electron-Compton profiles. A theoretical investigation is also presented in chapter six which details the advancements required in the spin polarised electron gun to measure an accurate spin-polarised EMS spectra of a ferromagnetic Fe sample.¶
Chapter 7 includes the summary of all the results presented and conclusions reached from the comparison of the measured EMS spectra and various theoretical calculations. A discussion is presented about the future directions and possibilities of the EMS technique.
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Yuan, Junhua Filippone Bradley. "Progress towards a high precision measurement of the neutron spin--electron angular correlation in polarized neutron beta decay with ultra-cold neutrons /". Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-01302006-153024.
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Jenkins, Anne Ceri. "Applications of spin-polarised relativistic scattering theory to the calculation of the electronic properties of heavy metals and alloys". Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321408.
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Dutta, Chiranjib. "MEASUREMENT OF SINGLE-TARGET SPIN ASYMMETRIES IN THE ELECTROPRODUCTION OF NEGATIVE PIONS IN THE SEMI-INCLUSIVE DEEP INELASTIC REACTION n↑(e,éπ¯)X ON A TRANSVERSELY POLARIZED 3He TARGET". UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/29.
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The experiment E06010 measured the target single spin asymmetry (SSA) in the semiinclusive deep inelastic (SIDIS) n↑(e,éπ¯)X reaction with a transversely polarized 3He target as an effective neutron target. This is the very first independent measurement of the neutron SSA, following the measurements at HERMES and COMPASS on the proton and the deuteron. The experiment acquired data in Hall A at Jefferson Laboratory with a continuous electron beam of energy 5.9 GeV, probing the valence quark region, with x = 0.13→0.41, at Q2 = 1.31→3.1 GeV2. The two contributing mechanisms to the measured asymmetry, viz, the Collins effect and the Sivers effect can be realized through the variation of the asymmetry as a function of the Collins and Sivers angles. The neutron Collins and Sivers moments, associated with the azimuthal angular modulations, are extracted from the measured asymmetry for the very first time and are presented in this thesis. The kinematics of this experiment is comparable to the HERMES proton measurement. However, the COMPASS measurements on deuteron and proton are in the low-x region. The results of this experiment are crucial as the first step toward the extraction of quark transversity and Sivers distribution functions in SIDIS. With the existing results on proton and deuteron, these new results on neutron will provide powerful constraints on the transversity and Sivers distributions of both the u and d-quarks in the valence region.
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Grenier, Philippe. "Etude des fonctions de structure en spin du nucleon : l'experience e143 au slac". Clermont-Ferrand 2, 1995. http://www.theses.fr/1995CLF21720.
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Cette these decrit l'experience e143 de diffusion profondement inelastique d'electrons de 29 gev sur des cibles de nh#3 et nd#3 polarisees. Elle s'est deroulee aupres de l'accelerateur de stanford, en californie, et son but etait de mesurer les fonctions de structure polarisees g#1 et g#2 sur le proton et le deuton. Ces fonctions de structure permettent de tester la regle de somme de bjrken, regle fondamentale de la chromodynamique quantique. Elles nous renseignent egalement sur la structure en spin du nucleon et, en particulier, elles permettent d'acceder a la fraction du spin du nucleon portee par les quarks. Experimentalement, on determine les fonctions de structure par la mesure d'asymetries en sections efficaces. Nous obtenons pour le premier moment de g#1, pour le proton et le deuton, des valeurs qui se situent de deux a trois deviations standards en dessous des predictions d'ellis et jaffe, mais nos resultats confirment la validite de la regle de somme de bjrken et permettent d'estimer a environ 30% la contribution des quarks au spin du nucleon. Nos resultats sur g#2 semblent etre bien decrits par l'expression de wandzura et wilczek
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Bombor, Dirk. "Transportmessungen an Supraleitenden Eisenpniktiden und Heusler-Verbindungen". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-160515.
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In dieser Arbeit werden Resultate elektronischer Transportmessungen von supraleitenden Eisenpniktiden und ferromagnetischen Heusler-Verbindungen diskutiert. Die Eisenpniktide sind eine neuartige Klassen von Hochtemperatursupraleitern, deren Eigenschaften sich aus einem Zusammenspiel von Supraleitung und Magnetismus ergeben. Während die sogenannten 122-Pniktide Antiferromagnetismus aufweisen und unter Dotierung in einen supraleitenden Zustand übergehen, konnte in dotiertem LiFeAs Ferromagnetismus beobachtet werden. Undotiert hingegen zeigt dieses Material interessante supraleitende Eigenschaften. Die Heusler-Verbindungen sind u.a. durch ihren Ferromagnetismus bekannt. Das hier untersuchte Co2FeSi ist einer der stärksten Ferromagnete. Der in diesem Material vorhergesagte vollständig spinpolarisierte elektronische Transport, d.h. alle Leitungselektronen besitzen den gleichen Spin, konnte nachgewiesen werden. Die hier genannten Eigenschaften können exzellent mit der Methode der elektronischen Transportmessungen untersucht werden. Deren Ergebnisse aus Messungen an Einkristallen werden in dieser Arbeit diskutiertIn this work, results of electronic transport measurements are discussed for superconducting iron pnictides as well as for ferromagnetic Heusler compounds. The iron pnictides are a recently discovered class of high temperature superconductors where magnetism might play a crucial role. While the 122-pnictides show antiferromagnetism and migrate to the superconducting state upon doping, ferromagnetism has been observed in doped LiFeAs. On the other hand, in the undoped state this material shows interesting superconducting properties. Among other propierties, Heusler compounds are well known due to their ferromagnetism. Co2FeSi, which was investigated in this work, is one of the strongest ferromagnets. Beside this, one predicts this compound to be a half-metallic ferromagnet with completely spin polarized electronic transport where all conducting electrons have the same spin. The here addressed properties can well be investigated with the method of electronic transport measurements, whose results on single crystals are discussed in this work
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ACHILLI, SIMONA. "Spectral properties of adsorbates on metal surfaces via the embedding method". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/10827.
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Adsorbates on metal surfaces have attracted recently the scientific interest both from a fundamental point of view (quantum confinement) and in perspective of application in technology. In particular the electronic properties of such reduced symmetry systems are strictly related to their low dimensionality. An accurate theoretical description of their spectral properties has necessarily to deal with the absence of periodicity that characterizes these systems in one (thin films) or more (adatoms) directions. The embedding method allows to overcome this drawback considering a really infinite system both on vacuum and bulk side. In this thesis the ab initio spectral properties of single adatoms (alkali-metal atom and Ba) on Cu(111) and thin overlayers (K/Cu(111), Bi/Cu(100), O/Fe(100)) are analyzed, also in comparison with experimental results. The capabilities of the theoretical method adopted allow to evidence the role of the substrate band structure on the adsorbates induced electronic states. In particular the aspects related to the resonant charge transfer from the adsorbate's states to the bulk continuum are analyzed. This process represents an elastic decay channel for the surface electronic states and contributes to the elastic lifetime, that we can estimate according to the description of a continuous substrate band structure. The results presented for single adatoms evidence the blockade effect that a surface projected energy gap of the substrate produces on the resonant charge transfer. On the other hand the results relative to the overlayer allows to analyze the complex hybridization mechanism between surface features and substrate states in different points of the surface Brillouin zone.
In addition the theoretical description of the electronic properties of overlayers on metal surfaces is devoted in this thesis also to the simulation of experimental findings, namely STM and STS images and photoemission spectra, showing the predictive character of the theoretical approach used.
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Hasch, Delia. "Messung der polarisierten Strukturfunktion g1(x, Q 2) des Protons mit dem HERMES-Experiment". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 1999. http://dx.doi.org/10.18452/14523.
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Die vorliegende Arbeit beschreibt die Messung der polarisierten Strukturfunktion g1p des Protons in der polarisationsabh"angigen tief inelastischen Positron-Proton-Streuung bei einer Schwerpunktenergie von 7.5 GeV. Die Analyse umfasst die 1997 mit dem Hermes-Experiment am Hera-Positronring aufgezeichneten Daten der Streuung polarisierter Positronen der Energie 27.6 GeV an einem polarisierten Wasserstofftarget. Aus den Z"ahlraten der inklusiv nachgewiesenen, selektierten Positronen f"ur die parallele und die antiparallele Ausrichtung der Spinvektoren von Strahlteilchen und Targetatomen wurde die Streuquerschnitts- Asymmetrie der Positron-Proton-Streuung bestimmt. In verschiedenen Korrekturverfahren wurden Untergrundprozesse, Spektrometereinfl"usse sowie Strahlungskorrekturen ber"ucksichtigt. Die Untergrundkorrekturen wurden aus den Daten, die Spektrometerkorrekturen aus einer Monte-Carlo- Simulation ermittelt. Die Abh"angigkeit der Monte-Carlo- und Strahlungskorrekturen von der gew"ahlten Modell-Asymmetrie zur Beschreibung der polarisationsabh"angigen Effekte wurde durch die Anwendung eines iterativen Verfahrens minimiert. Aus der vollst"andig korrigierten Streuquerschnitts-Asymmetrie wurde die Asymmetrie g1/F1 im kinematischen Bereich 0.021 < x < 0.85 und Q2 > 0.8 GeV^2 mit einer systematischen Unsicherheit von etwa 8% bei einer statistischen Genauigkeit von 6% bis 20%, ansteigend f"ur abnehmende x-Werte, bestimmt. Die aus g1/F1 berechnete polarisierte Strukturfunktion g1p(x,Q2) wird, unter der Annahme einer von q2 unabh"angigen Asymmetry g1/F1, zu einem festen Wert Q2_0 entwickelt. Ihr erstes Moment im gemessenen x-Bereich betr"agt int_{0.021}^{0.85} dx g1p(x,Q2_0) = 0.122 =- 0.003 (stat) =- 0.010 (sys) at Q2_0 = 2.5 GeV^2. Der Vergleich mit den Werten des SMC-Experimentes am CERN und des E143-Experimentes am SLAC f"ur das erste Moment von g1p wurde unter Anwendung des gleichen Integrationsschemas f"ur den jeweils gemeinsam gemessenen x-Bereich sowie f"ur gleiche Q2_0 Werte durchgef"uhrt. Das Ergebnis der vorliegenden Analyse befindet sich, bezogen auf die statistische Genauigkeit der Messungen, in "Ubereinstimmung innerhalb von 0.6 bzw. 1.2 Standardabweichungen mit den Resultaten des E143- bzw. SMC-Experimentes. Durch Extrapolation der Strukturfunktion auf den gesamten x-Bereich [0,1] wird das erste Moment zu \int_{0}^{1} dx g1p(x,Q2_0) = 0.132 +- 0.003 (stat) +- 0.010 (sys) +- 0.006 (extr) bestimmt, wobei der zus"atzliche Fehler die Unsicherheit in der Extrapolation x -> 0 wiedergibt. Die Interpretation der vorliegenden Messung im Rahmen des Quark-Parton-Modells unter Ber"ucksichtigung von QCD-Korrekturen der Ordnung O(alphaS^3) ergibt einen Beitrag der Quarks zum Gesamtspin des Nukleons von (30 +- 10)% f"ur Q2_0 = 2.5 GeV^2. Dieses Ergebnis entspricht einer Abweichung von der Ellis-Jaffe-Vorhersage um 2.5 Standardabweichungen, bezogen auf den angegebenen Gesamtfehler, und f"uhrt im Kontext des Quark-Parton-Modells zur Interpretation negativ polarisierter Strange-Seequarks mit einem Beitrag von (-9 +- 4)% f"ur Q2_0 = 2.5 GeV^2. Von verschiedenen Gruppen werden aus QCD-Analysen unterschiedlicher Datens"atze Beitr"age der Quarks zum Nukleonspin von 19% bis 44% angegeben. Unter Hinzunahme der Hermes-Messung der polarisierten Neutronstrukturfunktion g1n wurde der Wert der fundamentalen Bjorken-Summenregel f"ur Q2_0 = 2.5 GeV^2 bestimmt. Dieser Wert befindet sich, bei einer auf den Gesamtfehler bezogenen Genauigkeit von 13%, innerhalb von 0.5 Standardabweichungen in "Ubereinstimmung mit der theoretischen Vorhersage, berechnet unter Ber"ucksichtigung von QCD-Korrekturen der Ordnung O(\alphaS^3).The subject of this thesis is the measurement of the polarised structure function g1p of the proton in deeply inelastic positron-proton-scattering at a centre of mass energy of 7.5 GeV. The data used in the analysis were recorded during the 1997 running period of the Hermes experiment using a longitudinally nuclear polarised hydrogen target in the 27.6 GeV Hera polarised positron storage ring. The cross section asymmetry of positron-proton-scattering has been measured by counting the number of inclusively reconstructed and selected positrons with target spin vector parallel or antiparallel to the beam spin direction. Background processes, spectrometer effects, and radiative corrections have been taken into account by applying different correction procedures. Here background corrections were determined from data while spectrometer corrections were computed from Monte Carlo simulation. The dependence of Monte Carlo and radiative corrections on the model asymmetry chosen to describe polarisation dependent effects has been minimised by applying an iterative procedure. From the fully corrected cross section asymmetry the asymmetry g1/F1 has been computed in the kinematic region 0.021 < x < 0.85 and Q2 > 0.8 GeV^2 with a systematic uncertainty of 8% and a statistical accuracy of 6% to 20%, raising for decreasing x values. The polarised structure function g1p(x,Q2), determined from the asymmetry g1/F1 , was evoluted to a common Q2_0 value assuming g1/F1 to be independent of Q2. Its first moment evaluated in the measured x region is int_{0.021}^{0.85} dx g1p(x,Q2_0) = 0.122 =- 0.003 (stat) =- 0.010 (sys) at Q2_0 = 2.5 GeV^2. This result has been compared with those from E143 at SLAC and from SMC at CERN, both calculated with the same integration scheme and for the kinematic range of Hermes. With respect to the statistical uncertainties the agreement is better than 0.6 and 1.2 standard deviations, respectively. Extrapolation over the entire x range [0,1] yield for the first moment\int_{0}^{1} dx g1p(x,Q2_0) = 0.132 +- 0.003 (stat) +- 0.010 (sys) +- 0.006 (extr) where the additional error gives the uncertainty in the extrapolation x -> 0. The interpretation of this measurement in the framework of the quark parton model taking QCD corrections of the order O(alphaS^3) into account results in a contribution of the quarks to the total nucleon spin of (30 +- 10)% at Q2_0 = 2.5 GeV^2. This result corresponds to a deviation from the Ellis-Jaffe prediction by 2.5 standard deviation regarding the given total uncertainty. Within the quark parton model the deviation can be interpreted as negative polarisation of the strange sea quarks with a contribution of (-9 +- 4)% at Q2_0 = 2.5 GeV^2. Different groups give contributions of the quarks to the nucleon spin of 19% to 44% which were obtained from QCD analyses of various data sets. The fundamental Bjorken sum rule has been determined at Q2_0 = 2.5 GeV^2 using the Hermes measurement of the polarised neutron structure function g1n. With respect to the experimental accuracy of 13 %, the result agrees within 0.5 standard deviation with the theoretical prediction taking QCD corrections of the order O(alphaS^3) into account.
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Giacomoni, Laurence. "De la magnétorésistance géante à la magnétorésistance tunnel de multicouches magnétiques métalliques et métal/isolant". Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10156.
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Les etudes presentees dans ce memoire concernent le transport d'electrons polarises en spin dans les multicouches magnetiques et les effets qui en decoulent : la magnetoresistance geante dans les systemes metalliques et la magnetoresistance tunnel dans les systemes metal/oxyde. La magnetoresistance geante de multicouches nife/cu est etudiee dans les deux geometries de courant (planaire et perpendiculaire aux interfaces). Dans ces systemes, l'insertion de fines couches de co aux interfaces a pour effet de modifier le couplage indirect entre couches magnetiques successives et entraine une augmentation de l'amplitude de magnetoresistance. Parallelement, une etude de la variation angulaire de la resistance perpendiculaire a ete menee dans des vannes de spin a base de femn. Elle permet de confirmer le role predominant des electrons de caractere s et du mecanisme de diffusion dependante du spin dans le phenomene de magnetoresistance geante. L'effet tunnel d'electrons polarises en spin a ete etudie a la fois experimentalement et theoriquement. Les premiers resultats de caracterisations structurale, magnetique et de transport de multicouches discontinues (co/zro#2)#n sont presentes en fonction de l'epaisseur des couches magnetiques et des traitements thermiques. D'un point de vue theorique, nous avons etudie la magnetoresistance de jonctions magnetiques planaires de la forme mom' (m, m'=metaux ferromagnetiques, o=barriere d'oxyde) : introduction de couches antireflet selectives en spin aux interfaces et influence des epaisseurs des electrodes magnetiques.
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Yan, Zeyin. "Reconstruction de densité d'impulsion et détermination de la matrice densité réduite à un électron". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC001/document.
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La diffraction des rayons X à haute résolution (XRD) et celle des neutrons polarisés (PND) sont couramment utilisées pour modéliser les densités de charge et de spin dans l'espace des positions. Par ailleurs, la diffusion Compton et diffusion Compton magnétiques sont utilisées pour observer les plus diffus des électrons appariés et non appariés, en fournissant les profils Compton directionnels de charge (DCPs) et les profils Compton magnétique directionnels (DMCPs). Il est possible d'utiliser plusieurs DCPs et DMCPs non équivalents pour reconstituer la densité d'impulsion à deux ou trois dimensions. Puisque toutes ces techniques décrivent les mêmes électrons dans différentes représentations, nous nous concentrons sur l'association de la densité d'impulsion, reconstituée par DCPs (DMCPs) avec la densité de charge et spin, telle que déterminée à parties données XRD (PND).La confrontation théorie-experience, ou --plus rarement-- entre différentes techniques expérimentales, requièrent généralement les representations des densités reconstruites dans les espaces des positions et des impulsions. Le défi que pose la comparaison des résultats obtenus par calculs ab-initio et par des approches expérimentales (dans le cas de Nit(SMe)Ph) montre la nécessité de combiner plusieurs expériences et celle d'améliorer les modèles sur lesquels reposent les approches théoriques. Nous montrons que, dans le cas d'une densité de probabilité de présence d'électrons résolue en spin, une approche simple de type Hartree-Fock ou DFT ne suffit pas. Dans le cas de YTiO3, une analyse conjointe des espaces position et impulsion (PND & MCS) met en évidence un possible couplage ferromagnétique selon Ti--O1-Ti. Pour cela, une densité magnétique de "super-position" est proposée et s'avère permettre une vérification aisée de la cohérence entre densité de charge (spin) et densité de 'impulsion déterminées expérimentalement, sans la nécessité d'une étape ab-initio. Pour aller plus loin, un modèle "de Ti isolé", basé sur des coefficients orbitaux affinés par PND, souligne l'importance du couplage cohérent métal-oxygène nécessaire à rendre compte des observations dans l'espace des impulsions.La matrice densité réduite à un électron (1-RDM) est proposée comme socle de base permettant de systématiquement combiner les espaces des positions et des impulsions. Pour reconstruire cette 1-RDM à partir d'un calcul ab-initio périodique, une approche "cluster" est proposée. Il devient alors possible d'obtenir la 1-RDM théorique résolue en spin sur des chemins de liaison chimique particuliers. Ceci nous permet notamment de clarifier la différence entre les couplages Ti--O1--Ti et Ti-O2--Ti. Il est montré que l'importance des contributions du terme d'interaction entre les atomes (de métal et d'oxygène) est différente selon que l'on considère une représentation des propriétés dans l'espace des positions ou des impulsions. Ceci est clairement observé dans les liaisons chimiques métal-oxygène et peut être illustré par une analyse séparant les contributions par orbitales. Les grandeurs decrivant les électrons dans l'espace des phases comme la fonction de Moyal peuvent également être déterminées par cette construction en "cluster". Ceci peut revêtir un intérêt particulier si la technique de diffusion Compton aux positions de Bragg pouvait être généralisée. Les premiers résultats d'un affinement de modèle simple de 1-RDM résolu en spin sont exposés. Le modèle respecte la N-représentabilité et est adapté pour plusieurs données expérimentales (telles que XRD, PND, CS, MCS ou XMD). Le potentiel de ce modèle n'est pas limité à une analyse en spin mais son usage est ici circonscrit à la description des électrons non appariés, ses limites sont identifiées et des voies d'amélioration future sont proposéesHigh resolution X-ray diffraction (XRD) and polarized neutron diffraction (PND) are commonly used to model charge and spin densities in position space. Additionally, Compton scattering (CS) and magnetic Compton scattering (MCS) are the main techniques to observe the most diffuse electrons and unpaired electrons by providing the “Directional Compton Profiles" (DCPs) and ”Directional magnetic Compton Profiles" (DMCPs), respectively. A set of such DCPs (DMCPs) can be used to reconstruct two-dimensional or three-dimensional electron momentum density. Since all these techniques describe the same electrons in different space representations, we concentrate on associating the electron momentum density reconstructed from DCPs (resp. DMCPs) with electron density refined using XRD (resp. PND) data.The confrontation between theory and experiment, or between different experiments, providing several sets of experimental data, is generally obtained from the reconstructed electron densities and compared with theoretical results in position and momentum spaces. The challenge of comparing the results obtained by ab-initio computations and experimental approaches (in the Nit(SMe)Ph case) shows the necessity of a multiple experiments joint refinement and also the improvement of theoretical computation models. It proves that, in the case of a spin resolved electron density, a mere Hartree-Fock or DFT approach is not sufficient. In the YTiO3 case, a joint analysis of position and momentum spaces (PND & MCS) highlights the possible ferromagnetic pathway along Ti--O1--Ti. Therefore, a “super-position" spin density is proposed and proves to allow cross-checking the coherence between experimental electron densities in posittion and momentum spaces, without having recourse to ab initio results. Furthermore, an ”isolated Ti model" based on PND refined orbital coefficients emphasizes the importance of metal-oxygen coherent coupling to properly account for observations in momentum space.A one-electron reduced density matrix (1-RDM) approach is proposed as a fundamental basis for systematically combining position and momentum spaces. To reconstruct 1-RDM from a periodic ab initio computation, an "iterative cluster" approach is proposed. On this basis, it becomes possible to obtain a theoretical spin resolved 1-RDM along specific chemical bonding paths. It allows a clarification of the difference between Ti--O1--Ti and Ti--O2--Ti spin couplings in YTiO3. It shows that interaction contributions between atoms (metal and oxygen atoms) are different depending on whether the property is represented in position or momentum spaces. This is clearly observed in metal-oxygen chemical bonds and can be illustrated by an orbital resolved contribution analysis. Quantities for electron descriptions in phase space, such as the Moyal function, can also be determinerd by this "cluster model", which might be of particular interest if Compton scattering in Bragg positions could be generalized. The preliminary results of a simple spin resolved 1-RDM refinement model are exposed. The model respects the N-representability and is adapted for various experimental data (e.g.: XRD, PND, CS, MCS, XMD etc.). The potential of this model is not limited to a spin analysis but its use is limited here to the unpaired electrons description. The limitations of this model are analysed and possible improvements in the future are also proposed
44
Jones, Cathleen Elaine. "A measurement of the spin-dependent asymmetry in quasielastic scattering of polarized electrons from polarized ^3He". Thesis, 1992. https://thesis.library.caltech.edu/6686/1/Jones_ce_1992.pdf.
Pełny tekst źródłaStreszczenie:
The results of a measurement of the spin-dependent asymmetry in inclusive quasielastic scattering of polarized electrons from polarized ^3He are reported. The experiment was run at the MIT-Bates Linear Accelerator Center using a beam of longitudinally polarized electrons at an incident energy of 574 MeV. Scattered electrons were detected independently in two spectrometers, with one measurement sensitive to the spin-dependent transverse quasielastic response function, R_(T'), at Q^2 = 0.20 (GeV/c)^2 and the other sensitive to the spin-dependent interference response function, R(TL'), at Q^2 = 0.16 (GeV/c)^2. The asymmetry in the elastic kinematic region was also measured at a scattering angle of 44°. The target was gaseous ^3He polarized through optical pumping of metastable 2^3S atoms, with the polarization transferred to the ground state atoms through metastability exchange collisions. The target, the first of its kind to be used for an electron scattering experiment, is described in detail.
The analysis of the helicity dependent cross section data and the extraction of the quasielastic asymmetry are discussed. The measured quasielastic asymmetries are compared to theories that model the spin-dependent properties of ^3He as being dominated by the electromagnetic properties of the neutron, and are found to agree with the models. A value of the neutron electric form factor at Q^2 = 0.16 (GeV/c)^2 is extracted from the measured asymmetry sensitive to R_(TL'), demonstrating a new technique for accessing information about the neutron.
45
Löffler, Wolfgang [Verfasser]. "Electrical preparation of spin-polarized electrons in semiconductor quantum dots / von Wolfgang Löffler". 2008. http://d-nb.info/994895925/34.
Pełny tekst źródła
46
Rutherford, George Henry. "An intense source of spin-polarized electrons based on an optically-pumped flowing helium afterglow". Thesis, 1989. http://hdl.handle.net/1911/13388.
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The optimization of an optically-pumped, flowing helium afterglow for use as a high-current dc polarized electron source with high electron spin polarization is described. The atomic electron spins of He (2$\sp3\rm S\sb1$) metastable atoms created by a microwave discharge are aligned in the presence of a weak magnetic field by circularly polarized radiation from a recently developed LNA laser. The polarized outer 2s electrons are liberated in spin-conserving Penning ionization reactions with CO$\sb2$ and are extracted from the flow tube for polarization analysis. Polarizations approaching 90% were obtained at currents below.1 $\mu$A, falling gradually to 70% at 20 $\mu$A. Comparisons with other sources, chiefly photoemission from GaAs, suggest that for most applications requiring dc currents less than 50 $\mu$A, the flowing afterglow source is superior. Possible future improvements to the present source are also discussed.
47
Guite, Chinkhanlun. "Experimental Studies Of Electron Spin Dynamics In Semiconductors Using A Novel Radio Frequency Detection Technique". Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2458.
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A novel experimental setup has been realized to measure weak magnetic moments which can be modulated at radio frequencies (~1–5 MHz). Using an optimized radio-frequency (RF) pickup coil and lock-in amplifier, an experimental sensitivity of 10 -15 Am2 corresponding to 10 -18 emu has been demonstrated with a one second time constant. The detection limit at room temperature is 9.3 10 -16 Am2/√Hz limited by Johnson noise of the coil. In order to demonstrate the sensitivity of this technique it was used to electrically detect the polarized spins in semiconductors in zero applied magnetic fields. For example in GaAs, the magnetic moment due to a small number (~ 7 x 108) of spin polarized electrons generated by polarization modulated optical radiation was detected.
Spin polarization was generated by optical injection using circularly polarized light which is modulated rapidly using an electro-optic cell. The modulated spin polarization generates a weak time-varying magnetic field which is detected by the sensitive radio-frequency coil. Using a radio-frequency lock-in amplifier, clear signals were obtained for bulk GaAs and Ge samples from which an optical spin orientation efficiency of ~ 10–20% could be determined for Ge at 1342 nm excitation wavelength at 127 K. In the presence of a small external magnetic field, the signal decayed according to the Hanle Effect, from which a spin lifetime of 4.6 ± 1.0 ns for electrons in bulk Ge at 127 K was extracted. The spin dynamics in n-Ge was further explored and the temperature dependence of the spin lifetime was plotted for a temperature range of about 90 K to 180 K. The temperature dependence of the optical pumping efficiency was also measured though no quantitative conclusions could be derived.
The signals observed for semi-insulating GaAs, n-GaAs, GaSb and CdTe which are direct gap semiconductors are much larger than expected (almost two orders of magnitude). An attempt was made to explain this unexpected behavior of these direct gap semiconductors using the spin hall effect.
48
Guite, Chinkhanlun. "Experimental Studies Of Electron Spin Dynamics In Semiconductors Using A Novel Radio Frequency Detection Technique". Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2458.
Pełny tekst źródłaStreszczenie:
A novel experimental setup has been realized to measure weak magnetic moments which can be modulated at radio frequencies (~1–5 MHz). Using an optimized radio-frequency (RF) pickup coil and lock-in amplifier, an experimental sensitivity of 10 -15 Am2 corresponding to 10 -18 emu has been demonstrated with a one second time constant. The detection limit at room temperature is 9.3 10 -16 Am2/√Hz limited by Johnson noise of the coil. In order to demonstrate the sensitivity of this technique it was used to electrically detect the polarized spins in semiconductors in zero applied magnetic fields. For example in GaAs, the magnetic moment due to a small number (~ 7 x 108) of spin polarized electrons generated by polarization modulated optical radiation was detected.
Spin polarization was generated by optical injection using circularly polarized light which is modulated rapidly using an electro-optic cell. The modulated spin polarization generates a weak time-varying magnetic field which is detected by the sensitive radio-frequency coil. Using a radio-frequency lock-in amplifier, clear signals were obtained for bulk GaAs and Ge samples from which an optical spin orientation efficiency of ~ 10–20% could be determined for Ge at 1342 nm excitation wavelength at 127 K. In the presence of a small external magnetic field, the signal decayed according to the Hanle Effect, from which a spin lifetime of 4.6 ± 1.0 ns for electrons in bulk Ge at 127 K was extracted. The spin dynamics in n-Ge was further explored and the temperature dependence of the spin lifetime was plotted for a temperature range of about 90 K to 180 K. The temperature dependence of the optical pumping efficiency was also measured though no quantitative conclusions could be derived.
The signals observed for semi-insulating GaAs, n-GaAs, GaSb and CdTe which are direct gap semiconductors are much larger than expected (almost two orders of magnitude). An attempt was made to explain this unexpected behavior of these direct gap semiconductors using the spin hall effect.
49
Pradeep, A. V. "Development of a Spin-Polarized Low Energy Electron Diffraction System and Investigation on Spin-Orbit and Exchange Interactions on Ir(100) and Ultrathin Fe(100) Grown on Ir(100)". Thesis, 2016. http://etd.iisc.ac.in/handle/2005/3202.
Pełny tekst źródłaStreszczenie:
Spin-polarized electron beam has not yet been produced from an unpolarized electron beam using Stern-Gerlach type spin filter, because of the Lorentz force and Heisenberg uncertainty principle. At present, electron spin detectors and filters work on the basis of spin-dependent scattering of an electron beam from crystal surfaces. Single channel efficiencies of all the spin detectors for electrons are orders of magnitudes lower than the ideal one. Specular reflection type spin-polarized low energy electron diffraction (SPLEED)-spin detectors are having higher single channel efficiencies compared to the conventional Mott detectors. Moreover, multichannel detection can be realized from specular reflection type SPLEED-spin detectors. They have higher effective efficiency than the ideal spin detector. In order to develop specular reflection type spin filter, it is important to develop a spin-polarized low energy electron diffraction system. In addition, SPLEED system allows us to study the spin-orbit and exchange scattering at crystal surfaces.
The general direction of the thesis has been the development of spin-polarized low energy electron diffraction (SPLEED) system. This system has been used to investigate the spin-orbit interactions on Ir(100) surface and exchange interactions of Fe grown on Ir(100). The thesis is organized into chapters as follows.
Chapter 1 introduce the reader to some of the basic concepts of polarized electrons and the evolution of spin-polarized electron sources and detectors. Sources of polarized electrons are discussed with emphasis on photocathodes such as GaAs and strained GaAs. Widely used spin detector is the Mott detector which works in the higher energy range. The working principle of the Mott detector is discussed. Commonly used spin detector in the lower energy range is the LEED detector. The concept of the LEED detector is also discussed. Working principle and recent developments of specular reflection type SPLEED spin filters are introduced. Evolution of electron spin detector is discussed towards the end of the chapter.
Chapter 2 discusses about the two instruments designed and developed during the course of the thesis. The first one is a spin-polarized low energy electron diffraction system working in the reflected electron pulse counting mode in UHV. This system is capable of measuring spin asymmetries due to spin-orbit interaction and exchange interaction. This instrument is useful in understanding structure and magnetism at surfaces as well as helps to develop new spin polarimeter based on SPLEED by evaluating spin asymmetries from different surfaces. All instruments connected to SPLEED system, measurement protocol and controlling software are discussed with some details. Along with this, standard characterization tools such as X-ray diffraction and magneto-optic Kerr effect measurements are discussed. The second instrument is a novel quadratic magneto-optic Kerr effect measurement system using permanent magnets, which is simple, compact and cost-effective. We have used rotating field method to extract QMOKE component in saturation. So there is no need for precise real-time measurement of magnitude and direction of the magnetic field as in the case of vector magnet. This instrument can easily quantify QMOKE coefficients for ferrimagnetic and ferromagnetic thin films and single crystals.
Chapter 3 discusses SPLEED experiments carried out on Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. The surface structure and surface preparation techniques are discussed. The stability of the Ir(100)-(1×5)-Hex surface is evaluated by monitoring the spin asymmetry as the function of time. Within 25 hours after the surface preparation, the profile of the spin asymmetry and the reflected electron count for Ir(100)-(1×5)-Hex surface resembles that of hydrogen adsorbed Ir(100)-(1×5)-H surface. The electron energy-angle of incidence landscape of reflectivity, spin asymmetry and figure of merit are recorded for Ir(100)-(1×2+2×1)-O surface. Many wide regions with a large figure of merit are identified in the E- landscape.
Chapter 4 reports SPLEED experiments carried out on Ir(100)-(1×5)-H surface. The comparison between asymmetries evaluated for the Ir(100)-(1×5)-Hex surface after 25 hours and Ir(100)-(1×5)-H surface suggests that Ir(100)-(1×5)-Hex surface is transforming to Ir(100)-(1×5)-H surface, in 25 hours. This can be due to the adsorption of more than four Langmuir of residual hydrogen during this time. The energy-angle landscape of reflectivity, asymmetry and figure of merit are recorded for Ir(100)-(1×5)-H surface in an energy range 20 eV to 100 eV and angle range 10 to 60 . Many regions are identified as the working point for specular reflection type spin filter based on SPLEED. The surface structure and surface preparation techniques are discussed. The stability of the surface is also evaluated.
Chapter 5 investigates the growth and magnetic properties of Fe(100) film on Ir(100)-(1×1), Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. LEED, MEED, LMOKE and QMOKE studies were presented. The growth is found to be layer-by-layer at least up to 20 monolayers (ML) at room temperature. At higher deposition temperature, the MEED oscillations disappear around 3-5 ML. Magnetic anisotropy of the Fe(100) film grown on Ir(100)-(1×2+2×1)-O surfaces is evaluated using LMOKE measurement using Kerr microscope. Simultaneous in-situ LMOKE and MEED measurements were carried out during the deposition. Ferromagnetic ordering with an in-plane easy axis starts above 4.5 ML at room temperature. The Kerr rotation normalized by thickness is evaluated in the pseudomorphic regime and strain relaxed regime. The probing depth of the MOKE is found to be around 14 nm in Fe(100)/Ir(100). An antisymmetric component is observed in the re-magnetization loop measured using MOKE. This antisymmetric loop arises due to the quadratic magneto-optic coupling which is separated by symmetrization and antisymmetrization procedure. The observed quadratic magneto-optic coupling suggests that the analysis based on the assumption that the magneto-optic coupling is linear in magnetization has to be modified. In order to quantify the quadratic magneto-optic coupling parameters, a QMOKE measurement system is developed and measurements were carried out.
Chapter 6 discusses SPLEED experiments carried out on various thicknesses of Fe(100) film. Fe(100) films grown on Ir(100) substrate with the thickness less than or equal to 4 ML is not ferromagnetic with in-plane easy axis at room temperature. The non-zero exchange asymmetry observed for 5 ML and above indicates the presence of ferromagnetic ordering. A difference in the profile of exchange asymmetry is observed between pseudomorphic and strain relaxed regime. Large spin-orbit asymmetry is observed for 1 ML and 2 ML Fe(100) which is unexpected from a low atomic number (Z) material. The reason for large spin-orbit asymmetry is still unknown. The energy-angle landscape of reflectivity, exchange asymmetry, spin-orbit asymmetry and figure of merit were evaluated for 21 ML of Fe(100). Many working points were identified for different types multichannel spin filter based on exchange interaction
Finally, the various results are summarized and a broad outlook is given.
50
Pradeep, A. V. "Development of a Spin-Polarized Low Energy Electron Diffraction System and Investigation on Spin-Orbit and Exchange Interactions on Ir(100) and Ultrathin Fe(100) Grown on Ir(100)". Thesis, 2016. http://hdl.handle.net/2005/3202.
Pełny tekst źródłaStreszczenie:
Spin-polarized electron beam has not yet been produced from an unpolarized electron beam using Stern-Gerlach type spin filter, because of the Lorentz force and Heisenberg uncertainty principle. At present, electron spin detectors and filters work on the basis of spin-dependent scattering of an electron beam from crystal surfaces. Single channel efficiencies of all the spin detectors for electrons are orders of magnitudes lower than the ideal one. Specular reflection type spin-polarized low energy electron diffraction (SPLEED)-spin detectors are having higher single channel efficiencies compared to the conventional Mott detectors. Moreover, multichannel detection can be realized from specular reflection type SPLEED-spin detectors. They have higher effective efficiency than the ideal spin detector. In order to develop specular reflection type spin filter, it is important to develop a spin-polarized low energy electron diffraction system. In addition, SPLEED system allows us to study the spin-orbit and exchange scattering at crystal surfaces.
The general direction of the thesis has been the development of spin-polarized low energy electron diffraction (SPLEED) system. This system has been used to investigate the spin-orbit interactions on Ir(100) surface and exchange interactions of Fe grown on Ir(100). The thesis is organized into chapters as follows.
Chapter 1 introduce the reader to some of the basic concepts of polarized electrons and the evolution of spin-polarized electron sources and detectors. Sources of polarized electrons are discussed with emphasis on photocathodes such as GaAs and strained GaAs. Widely used spin detector is the Mott detector which works in the higher energy range. The working principle of the Mott detector is discussed. Commonly used spin detector in the lower energy range is the LEED detector. The concept of the LEED detector is also discussed. Working principle and recent developments of specular reflection type SPLEED spin filters are introduced. Evolution of electron spin detector is discussed towards the end of the chapter.
Chapter 2 discusses about the two instruments designed and developed during the course of the thesis. The first one is a spin-polarized low energy electron diffraction system working in the reflected electron pulse counting mode in UHV. This system is capable of measuring spin asymmetries due to spin-orbit interaction and exchange interaction. This instrument is useful in understanding structure and magnetism at surfaces as well as helps to develop new spin polarimeter based on SPLEED by evaluating spin asymmetries from different surfaces. All instruments connected to SPLEED system, measurement protocol and controlling software are discussed with some details. Along with this, standard characterization tools such as X-ray diffraction and magneto-optic Kerr effect measurements are discussed. The second instrument is a novel quadratic magneto-optic Kerr effect measurement system using permanent magnets, which is simple, compact and cost-effective. We have used rotating field method to extract QMOKE component in saturation. So there is no need for precise real-time measurement of magnitude and direction of the magnetic field as in the case of vector magnet. This instrument can easily quantify QMOKE coefficients for ferrimagnetic and ferromagnetic thin films and single crystals.
Chapter 3 discusses SPLEED experiments carried out on Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. The surface structure and surface preparation techniques are discussed. The stability of the Ir(100)-(1×5)-Hex surface is evaluated by monitoring the spin asymmetry as the function of time. Within 25 hours after the surface preparation, the profile of the spin asymmetry and the reflected electron count for Ir(100)-(1×5)-Hex surface resembles that of hydrogen adsorbed Ir(100)-(1×5)-H surface. The electron energy-angle of incidence landscape of reflectivity, spin asymmetry and figure of merit are recorded for Ir(100)-(1×2+2×1)-O surface. Many wide regions with a large figure of merit are identified in the E- landscape.
Chapter 4 reports SPLEED experiments carried out on Ir(100)-(1×5)-H surface. The comparison between asymmetries evaluated for the Ir(100)-(1×5)-Hex surface after 25 hours and Ir(100)-(1×5)-H surface suggests that Ir(100)-(1×5)-Hex surface is transforming to Ir(100)-(1×5)-H surface, in 25 hours. This can be due to the adsorption of more than four Langmuir of residual hydrogen during this time. The energy-angle landscape of reflectivity, asymmetry and figure of merit are recorded for Ir(100)-(1×5)-H surface in an energy range 20 eV to 100 eV and angle range 10 to 60 . Many regions are identified as the working point for specular reflection type spin filter based on SPLEED. The surface structure and surface preparation techniques are discussed. The stability of the surface is also evaluated.
Chapter 5 investigates the growth and magnetic properties of Fe(100) film on Ir(100)-(1×1), Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. LEED, MEED, LMOKE and QMOKE studies were presented. The growth is found to be layer-by-layer at least up to 20 monolayers (ML) at room temperature. At higher deposition temperature, the MEED oscillations disappear around 3-5 ML. Magnetic anisotropy of the Fe(100) film grown on Ir(100)-(1×2+2×1)-O surfaces is evaluated using LMOKE measurement using Kerr microscope. Simultaneous in-situ LMOKE and MEED measurements were carried out during the deposition. Ferromagnetic ordering with an in-plane easy axis starts above 4.5 ML at room temperature. The Kerr rotation normalized by thickness is evaluated in the pseudomorphic regime and strain relaxed regime. The probing depth of the MOKE is found to be around 14 nm in Fe(100)/Ir(100). An antisymmetric component is observed in the re-magnetization loop measured using MOKE. This antisymmetric loop arises due to the quadratic magneto-optic coupling which is separated by symmetrization and antisymmetrization procedure. The observed quadratic magneto-optic coupling suggests that the analysis based on the assumption that the magneto-optic coupling is linear in magnetization has to be modified. In order to quantify the quadratic magneto-optic coupling parameters, a QMOKE measurement system is developed and measurements were carried out.
Chapter 6 discusses SPLEED experiments carried out on various thicknesses of Fe(100) film. Fe(100) films grown on Ir(100) substrate with the thickness less than or equal to 4 ML is not ferromagnetic with in-plane easy axis at room temperature. The non-zero exchange asymmetry observed for 5 ML and above indicates the presence of ferromagnetic ordering. A difference in the profile of exchange asymmetry is observed between pseudomorphic and strain relaxed regime. Large spin-orbit asymmetry is observed for 1 ML and 2 ML Fe(100) which is unexpected from a low atomic number (Z) material. The reason for large spin-orbit asymmetry is still unknown. The energy-angle landscape of reflectivity, exchange asymmetry, spin-orbit asymmetry and figure of merit were evaluated for 21 ML of Fe(100). Many working points were identified for different types multichannel spin filter based on exchange interaction
Finally, the various results are summarized and a broad outlook is given.