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Dempsey, Kari Jacqueline. "Magnetic and electronic transport properties of magnetic nanoparticles." Thesis, University of Leeds, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534426.
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Adams, Carl Philip. "Magnetic and transport properties of FeGe¦2." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0004/NQ41391.pdf.
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Ul-Haq, I. "Magnetic and transport properties of canonical spin glasses." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381742.
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Tejwani, Saurabh. "Thermodynamic and transport properties of non-magnetic particles in magnetic fluids." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54584.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references.
Magnetic composites, obtained on associating magnetic fluid with non-magnetic particles, offer interesting opportunities in separations, assemblies and other applications, where the microstructure of the composite can be altered reversibly by an external field without altering the composition. The goal of our work in this area is to develop computational and simulation tools to assist in the in-depth understanding of the thermodynamic and transport properties of such non-magnetic nanoparticles immersed in magnetic fluids under varying magnetic field conditions. Also, in this work we have studied the relaxation and magnetization characteristics of magnetic nanoparticle clusters in presence of low external magnetic fields. Theoretical analysis of such a complex system is difficult using conventional theories, and hence we have used Monte Carlo Simulations to explore these effects. We simulated the interactions between non-magnetic particles (1000 nm) and magnetic nanoparticles (10 nm and 20 nm diameter) dispersed in organic phase. We observed that the presence of the non-magnetic particle in the system induces magnetic non-homogeneity. The magnetic nanoparticles present in the equatorial place of the non-magnetic particle with reference to the applied magnetic field have a higher magnetization as compared to the particles in the polar region. This effect was much more dominant for 20 nm particles than 10nm particles, because the magnetic inter-particle interactions are much stronger for the larger particles. We have also studied the effect of radial distance from the nonmagnetic particle on the magnetization and radial distribution function characteristics of the magnetic nanoparticles.
(cont.) We have evaluated the magnetophoretic forces the non-magnetic particles experience when subjected to magnetic field gradient. We have identified such forces arising from the inter-particle interactions between the magnetic nanoparticles. These forces were found to be significant for larger magnetic particles, smaller non-magnetic particles and lower magnetic fields. Diffusion coefficients were evaluated for non-magnetic nanoparticles in magnetic fluids using Brownian Dynamics Simulation. The chain-like structures formed by magnetic nanoparticles introduce anisotropy in the system with the diffusion coefficients higher along the direction of applied external magnetic field and lower in the perpendicular direction. It was observed that the anisotropy increases with higher magnetic particle concentration and larger non-magnetic particles. Anisotropy is negligible for small sized magnetic particles for which the inter-particle interaction is smaller, increases with increasing magnetic particle size and becomes constant thereafter. Results were compared with theoretical predictions. Néel Relaxation was studied for magnetic nanoparticle clusters. Chain-like, spherical and planar clusters were evaluated for the relaxation times. For chain-like structures the relaxation times increase significantly on increasing the chain length and particle size. For spherical clusters the relaxation times were fairly similar to that of individual magnetic nanoparticles. Hence, such a fast relaxation makes them ideal candidates for HGMS separations, since they will be released quickly from the magnetic wires during the elution step.
(cont.) Also, we studied the magnetization characteristics of rectangular and hexagonal packing arrangements of magnetic clusters in presence of remnant fields. The hexagonal arrangement revealed a novel oscillatory behavior. A theoretical model was developed to predict the magnetic particle size beyond which the oscillations are observed.
by Saurabh Tejwani.
Ph.D.
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Matthes, Patrick. "Magnetic and Magneto-Transport Properties of Hard Magnetic Thin Film Systems." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-192683.
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The present thesis is about the investigation of ferromagnetic thin film systems with respect to exchange coupling, magnetization reversal behavior and effects appearing in magnetic heterostructures, namely the exchange bias and the giant magnetoresistance effect. For this purpose, DC magnetron sputtered thin films and multilayers with perpendicular magnetic anisotropy were prepared on single crystalline and rigid as well as flexible amorphous substrates. The first part concentrates on magnetic data storage applications based on the combination of the concept of bit patterned media and three dimensional magnetic memory, consisting of at least two exchange decoupled ferromagnetic storage layers. Here, [Co/Pt] multilayers, revealing different magnetic anisotropies, have been applied as storage layers and as spacer material Pt and Ru was employed. By the characterization of the magnetization reversal behavior the exchange coupling in dependence of the spacer layer thickness was studied. Furthermore, with regard to the concept of bit patterned media, the layers were also grown on self-assembled silica particles, leading to an exchange decoupled single-domain magnetic dot array, which was studied by magnetic force microscope imaging and angular dependent magneto-optic Kerr effect magnetometry to evaluate the reversal mechanism and its dependence on the array dimensions, mainly the diameter of the silica particles and layer thicknesses. To complete the study, micromagnetic simulations were performed to access smaller dimensions and to investigate the dependence of intralayer as well as interlayer coupling on the magnetization reversal of the dot array with multiple storage layers. The second part focuses on the investigation of the giant magnetoresistance effect in systems with perpendicular magnetic anisotropy, where L10 -chemically ordered FePt alloys and [Co/Pt] as well as [Co/Pd] multilayers were utilized. In case of FePt, where high temperatures during the deposition are necessary to induce the chemical ordering, diffusion and alloying of the spacer material often prevent a sufficient exchange decoupling of the ferromagnetic layers. However, with Ru as spacer material a giant magnetoresistance effect could be achieved. Large improvements of the magnetoresistive behavior of such trilayer structures are presented for [Co/Pt] and [Co/Pd] multilayers, which can be deposited at room temperature not limiting the choice of spacer as well as substrate material. Furthermore, in systems consisting of one ferromagnet with perpendicular magnetic anisotropy and one ferromagnet with in-plane magnetic easy axis, a linear and almost hysteresis-free field dependence of the electrical resistance was observed and the behavior for various thickness series has been intensively studied. Finally, the corrosion resistance in dependence of the capping layer material as well as the magnetoresistance of a strained flexible pseudo-spin-valve structure is presented. In addition, in chapter 2.5.2 an experimental study of an improved crystal growth of FePt at comparable low temperatures by molecular beam epitaxy and further promoted by a surfactant mediated growth using Sb is shown. Auger electron spectroscopy as well as Rutherford backscattering spectrometry were carried out to confirm the surface segregation of Sb and magnetic characterization revealed an increase of magnetic anisotropy in comparison to reference layers without SbDie vorliegende Dissertation beschäftigt sich mit der Untersuchung ferromagnetischer Dünnschichtsysteme im Hinblick auf die Austauchkopplung, das Ummagnetisierungsverhalten und Effekte wie z.B. den Exchange Bias Effekt oder den Riesenmagnetwiderstandseffekt (GMR), welche in derartigen Heterostrukturen auftreten können. Die Probenpräparation erfolgte mittels DC Magnetronsputtern, wobei auf einkristallinen aber auch flexiblen sowie starren amorphen Substraten abgeschieden wurde. Im ersten Teil der Arbeit werden Untersuchungen mit dem Hintergrund einer Anwendung als magnetischer Datenträger vorgestellt. Konkret werden hier die Konzepte Bit Patterned Media (BPM) und 3D Speicher miteinander kombiniert. Letzteres Konzept basiert auf der Verwendung wenigstens zweier austauschentkoppelter ferromagnetischer Schichten, für welche [Co/Pt] Multilagen mit unterschiedlicher magnetischer Anisotropie verwendet wurden. Als Zwischenschichtmaterial diente Pt und Ru. Durch die Charakterisierung des Ummagnetisierungsverhaltens wurde die Austauschkopplung in Abhängigkeit der Zwischenschichtdicke untersucht. Darüber hinaus wurden jene Schichtstapel zur Realisierung des BPM-Konzeptes auf selbstangeordnete SiO2 Partikel mit unterschiedlichen Durchmessern aufgebracht, durch welche sich lateral austauschentkoppelte, eindomänige magnetische Nanostrukturen erzeugen lassen. Zur Untersuchung des Ummagnetisierungsverhaltens und der jeweiligen Größenabhängigkeiten (maßgeblich Durchmesser und Schichtdicke) wurden diese mittels Magnetkraftmikroskopie sowie winkelabhängiger magnetooptischer Kerr Effekt Magnetometrie untersucht. Zur weiteren Vertiefung des Verständnisses noch kleinerer Strukturgrößen erfolgten mikromagnetische Simulationen, bei denen die magnetischen Wechselwirkungen lateral (benachbarte 3D Elemente) als auch vertikal (Wechselwirkungen ferromagnetischer Schichten innerhalb eines 3D Elementes) im Interesse standen, sowie deren Auswirkungen auf das Ummagnetisierungsverhalten des gesamten Feldes. Der Fokus des zweiten Teils liegt auf der Untersuchung des Riesenmagnetwiderstandseffektes in Systemen mit senkrechter Sensitivität. Dafür sind ferromagnetische Schichten mit senkrechter magnetischer Anisotropie nötig, wobei hier die chemisch geordnete L10-Phase der FePt Legierung und [Co/Pt] sowie [Co/Pd] Multilagen Anwendung fanden. Für eine chemische Ordnung der FePt Legierung sind hohe Temperaturen während der Schichtabscheidung notwendig, welche eine hinreichende Austauschentkopplung beider ferromagnetischer Schichten meist nicht gewährleisten. Grund dafür sind einsetzende Diffusionsprozesse als auch Legierungsbildungen mit dem Zwischenschichtmaterial. In der vorliegenden Arbeit konnte der GMR Effekt daher ausschließlich mit einer Ru Zwischenschicht in FePt basierten Trilagensystemen nachgewiesen und charakterisiert werden. Enorme Verbesserungen der magnetoresistiven Eigenschaften werden im Anschluss für [Co/Pt] und vor allem [Co/Pd] Multilagen vorgestellt. Diese Schichtsysteme mit senkrechter magnetischer Anisotropie können bei Raumtemperatur präpariert werden und stellen daher keine weiteren Anforderungen an das Zwischenschichtmaterial sowie die verwendeten Substrate. Hier wurden neben Systemen mit ausschließlich senkrechter magnetischer Anisotropie auch Systeme mit gekreuzten magnetischen Anisotropien intensiv untersucht, da diese durch einen linearen und weitgehend hysteresefreien R(H) Verlauf imHinblick auf Sensoranwendungen enorme Vorteile bieten. Letztendlich wurde die Korrosionsbeständigkeit in Abhängigkeit des Deckschichtmaterials als auch die mechanische Belastbarkeit von auf flexiblen Substraten abgeschiedenen GMR-Schichtstapeln untersucht. Zusätzlich wird in Kapitel 2.5.2 eine experimentelle Studie zum Surfactant-gesteuerten Wachstum der FePt Legierung mittels Molekularstrahlepitaxie vorgestellt. Als Surfactant dient Sb, wodurch die Kristallinität bei geringer Depositionstemperatur deutlich verbessert werden konnte. Die Oberflächensegregation von Sb wurde mittels Auger Elektronenspektroskopie und Rutherford Rückstreuspektrometrie verifiziert und die Charakterisierung magnetischer Eigenschaften belegt einen Anstieg der magnetischen Anisotropieenergie im Vergleich zu Referenzproben ohne Sb
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Matthes, Patrick. "Magnetic and Magneto-Transport Properties of Hard Magnetic Thin Film Systems." Doctoral thesis, Universitätsverlag der Technischen Universität Chemnitz, 2015. https://monarch.qucosa.de/id/qucosa%3A20376.
Full textAbstract:
The present thesis is about the investigation of ferromagnetic thin film systems with respect to exchange coupling, magnetization reversal behavior and effects appearing in magnetic heterostructures, namely the exchange bias and the giant magnetoresistance effect. For this purpose, DC magnetron sputtered thin films and multilayers with perpendicular magnetic anisotropy were prepared on single crystalline and rigid as well as flexible amorphous substrates.
The first part concentrates on magnetic data storage applications based on the combination of the concept of bit patterned media and three dimensional magnetic memory, consisting of at least two exchange decoupled ferromagnetic storage layers. Here, [Co/Pt] multilayers, revealing different magnetic anisotropies, have been applied as storage layers and as spacer material Pt and Ru was employed. By the characterization of the magnetization reversal behavior the exchange coupling in dependence of the spacer layer thickness was studied. Furthermore, with regard to the concept of bit patterned media, the layers were also grown on self-assembled silica particles, leading to an exchange decoupled single-domain magnetic dot array, which was studied by magnetic force microscope imaging and angular dependent magneto-optic Kerr effect magnetometry to evaluate the reversal mechanism and its dependence on the array dimensions, mainly the diameter of the silica particles and layer thicknesses. To complete the study, micromagnetic simulations were performed to access smaller dimensions and to investigate the dependence of intralayer as well as interlayer coupling on the magnetization reversal of the dot array with multiple storage layers.
The second part focuses on the investigation of the giant magnetoresistance effect in systems with perpendicular magnetic anisotropy, where L10 -chemically ordered FePt alloys and [Co/Pt] as well as [Co/Pd] multilayers were utilized. In case of FePt, where high temperatures during the deposition are necessary to induce the chemical ordering, diffusion and alloying of the spacer material often prevent a sufficient exchange decoupling of the ferromagnetic layers. However, with Ru as spacer material a giant magnetoresistance effect could be achieved. Large improvements of the magnetoresistive behavior of such trilayer structures are presented for [Co/Pt] and [Co/Pd] multilayers, which can be deposited at room temperature not limiting the choice of spacer as well as substrate material. Furthermore, in systems consisting of one ferromagnet with perpendicular magnetic anisotropy and one ferromagnet with in-plane magnetic easy axis, a linear and almost hysteresis-free field dependence of the electrical resistance was observed and the behavior for various thickness series has been intensively studied. Finally, the corrosion resistance in dependence of the capping layer material as well as the magnetoresistance of a strained flexible pseudo-spin-valve structure is presented.
In addition, in chapter 2.5.2 an experimental study of an improved crystal growth of FePt at comparable low temperatures by molecular beam epitaxy and further promoted by a surfactant mediated growth using Sb is shown. Auger electron spectroscopy as well as Rutherford backscattering spectrometry were carried out to confirm the surface segregation of Sb and magnetic characterization revealed an increase of magnetic anisotropy in comparison to reference layers without Sb.Die vorliegende Dissertation beschäftigt sich mit der Untersuchung ferromagnetischer Dünnschichtsysteme im Hinblick auf die Austauchkopplung, das Ummagnetisierungsverhalten und Effekte wie z.B. den Exchange Bias Effekt oder den Riesenmagnetwiderstandseffekt (GMR), welche in derartigen Heterostrukturen auftreten können. Die Probenpräparation erfolgte mittels DC Magnetronsputtern, wobei auf einkristallinen aber auch flexiblen sowie starren amorphen Substraten abgeschieden wurde. Im ersten Teil der Arbeit werden Untersuchungen mit dem Hintergrund einer Anwendung als magnetischer Datenträger vorgestellt. Konkret werden hier die Konzepte Bit Patterned Media (BPM) und 3D Speicher miteinander kombiniert. Letzteres Konzept basiert auf der Verwendung wenigstens zweier austauschentkoppelter ferromagnetischer Schichten, für welche [Co/Pt] Multilagen mit unterschiedlicher magnetischer Anisotropie verwendet wurden. Als Zwischenschichtmaterial diente Pt und Ru. Durch die Charakterisierung des Ummagnetisierungsverhaltens wurde die Austauschkopplung in Abhängigkeit der Zwischenschichtdicke untersucht. Darüber hinaus wurden jene Schichtstapel zur Realisierung des BPM-Konzeptes auf selbstangeordnete SiO2 Partikel mit unterschiedlichen Durchmessern aufgebracht, durch welche sich lateral austauschentkoppelte, eindomänige magnetische Nanostrukturen erzeugen lassen. Zur Untersuchung des Ummagnetisierungsverhaltens und der jeweiligen Größenabhängigkeiten (maßgeblich Durchmesser und Schichtdicke) wurden diese mittels Magnetkraftmikroskopie sowie winkelabhängiger magnetooptischer Kerr Effekt Magnetometrie untersucht. Zur weiteren Vertiefung des Verständnisses noch kleinerer Strukturgrößen erfolgten mikromagnetische Simulationen, bei denen die magnetischen Wechselwirkungen lateral (benachbarte 3D Elemente) als auch vertikal (Wechselwirkungen ferromagnetischer Schichten innerhalb eines 3D Elementes) im Interesse standen, sowie deren Auswirkungen auf das Ummagnetisierungsverhalten des gesamten Feldes. Der Fokus des zweiten Teils liegt auf der Untersuchung des Riesenmagnetwiderstandseffektes in Systemen mit senkrechter Sensitivität. Dafür sind ferromagnetische Schichten mit senkrechter magnetischer Anisotropie nötig, wobei hier die chemisch geordnete L10-Phase der FePt Legierung und [Co/Pt] sowie [Co/Pd] Multilagen Anwendung fanden. Für eine chemische Ordnung der FePt Legierung sind hohe Temperaturen während der Schichtabscheidung notwendig, welche eine hinreichende Austauschentkopplung beider ferromagnetischer Schichten meist nicht gewährleisten. Grund dafür sind einsetzende Diffusionsprozesse als auch Legierungsbildungen mit dem Zwischenschichtmaterial. In der vorliegenden Arbeit konnte der GMR Effekt daher ausschließlich mit einer Ru Zwischenschicht in FePt basierten Trilagensystemen nachgewiesen und charakterisiert werden. Enorme Verbesserungen der magnetoresistiven Eigenschaften werden im Anschluss für [Co/Pt] und vor allem [Co/Pd] Multilagen vorgestellt. Diese Schichtsysteme mit senkrechter magnetischer Anisotropie können bei Raumtemperatur präpariert werden und stellen daher keine weiteren Anforderungen an das Zwischenschichtmaterial sowie die verwendeten Substrate. Hier wurden neben Systemen mit ausschließlich senkrechter magnetischer Anisotropie auch Systeme mit gekreuzten magnetischen Anisotropien intensiv untersucht, da diese durch einen linearen und weitgehend hysteresefreien R(H) Verlauf imHinblick auf Sensoranwendungen enorme Vorteile bieten. Letztendlich wurde die Korrosionsbeständigkeit in Abhängigkeit des Deckschichtmaterials als auch die mechanische Belastbarkeit von auf flexiblen Substraten abgeschiedenen GMR-Schichtstapeln untersucht. Zusätzlich wird in Kapitel 2.5.2 eine experimentelle Studie zum Surfactant-gesteuerten Wachstum der FePt Legierung mittels Molekularstrahlepitaxie vorgestellt. Als Surfactant dient Sb, wodurch die Kristallinität bei geringer Depositionstemperatur deutlich verbessert werden konnte. Die Oberflächensegregation von Sb wurde mittels Auger Elektronenspektroskopie und Rutherford Rückstreuspektrometrie verifiziert und die Charakterisierung magnetischer Eigenschaften belegt einen Anstieg der magnetischen Anisotropieenergie im Vergleich zu Referenzproben ohne Sb.
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Hong, Yuanjia. "Magnetic and Transport Properties of Oxide Thin Films." ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/615.
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My dissertation research focuses on the investigation of the transport and magnetic properties of transition metal and rare earth doped oxides, particularly SnO2 and HfO2 thin films. Cr- and Fe-doped SnO2 films were deposited on Al2O3 substrates by pulsed-laser deposition. Xray- diffraction patterns (XRD) show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction peaks of Cr-doped samples exhibit a systematic shift toward higher angles with increasing Cr concentration. This indicates that Cr dissolves in SnO2. On the other hand, there is no obvious shift of the diffraction peaks of the Fe-doped samples. The magnetization curves indicate that the Cr-doped SnO2 films are paramagnetic at 300 and 5 K. The Fe-doped SnO2 samples exhibit ferromagnetic behaviour at 300 and 5 K. Zero-field-cooled and field-cooled curves indicate super paramagnetic behavior above the blocking temperature of 100 K, suggesting that it is possible that there are ferromagnetic particles in the Fe-doped films. It was found that a Sn0.98Cr0.02O2 film became ferromagnetic at room temperature after annealing in H2. We have calculated the activation energy and found it decreasing with the annealing, which is explained by the increased oxygen vacancies/defects due to the H2 treatment of the films. The ferromagnetism may be associated with the presence of oxygen vacancies although AMR was not observed in the samples. Pure HfO2 and Gd-doped HfO2 thin films have been grown on different single crystal substrates by pulsed laser deposition. XRD patterns show that the pure HfO2 thin films are of single monoclinic phase. Gd-doped HfO2 films have the same XRD patterns except that their diffraction peaks have a shift toward lower angles, which indicates that Gd dissolves in HfO2. Transmission electron microscopy images show a columnar growth of the films. Very weak ferromagnetism is observed in pure and Gd-doped HfO2 films on different substrates at 300 and 5 K, which is attributed to either impure target materials or signals from the substrates. The magnetic properties do not change significantly with post deposition annealing of the HfO2 films.
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Schleser, Roland. "Magnetostrictive, magnetic and transport properties of correlated electron systems." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964073102.
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Warnatz, Tobias. "Magnetic Coupling and Transport Properties of Fe/MgO Superlattices." Thesis, Uppsala universitet, Materialfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-262549.
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Zeissler, Katharina. "Magnetic and electrical transport properties of artificial spin ice." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/25524.
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This thesis explores the mechanisms of the magnetic reversal of permalloy artificial spin ice arrays. The main research foci include the influence of domain wall propagation on the magnetic reversal of honeycomb artificial spin ice, the low temperature behaviour of honeycomb artificial spin ice and the classification of inverse permalloy opals as three dimensional artificial spin ice. Room temperature imaging of the magnetisation configuration of the nanobars through the magnetic reversal, via scanning transmission X-ray microscopy, photoemission electron microscopy and Lorentz transmission electron microscopy, showed non random domain wall propagation through the frustrated vertices of the honeycomb artificial spin ice arrays. OOMMF simulations suggest that the origin of such non-randomness lies in the domain wall chirality. Boundary conditions necessary for domain wall injection into artificial spin ice arrays were investigated. A reduction of the edge nanobars width of 2/3 was needed to prevent random domain wall nucleation from the array edges. Electrical transport measurements showed evidence of a change in the magnetic reversal, driven by domain wall propagation, of honeycomb permalloy artificial spin ice below 15 K. The transition temperature was found to be proportional to the square of the saturation magnetisation of the ferromagnetic material used. The change in the magnetic reversal was associated with the non-random vertex domain wall positioning below the transition temperature due to the influence of vertex dipole interactions. Room temperature Lorentz transmission electron microscopy images and temperature dependent electrical transport measurements of three dimensional permalloy inverse opals showed the potential of magnetic inverse opals to act as three dimensional artificial spin ice systems.
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Platt, Christopher L. "Magnetic and transport properties of spin-dependent tunnel junctions /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952654.
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Notario, Estévez Almudena. "Theoretical Study of Polyoxovanadates: Analysis of structural, magnetic and transport properties." Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/672748.
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Noves aplicacions tecnològiques per a l’electrònica estan sent investigades per la comunitat científica. Tenen com a objectiu cobrir les noves demandes de sistemes electrònics més petits i potents, com ordinadors o telèfons mòbils, presents en la nostra vida diària. Entre la gran varietat de materials candidats que en desenvolupament per a aquests fins, els polioxovanadats (POVs) constitueixen una família prometedora per les seves característiques químiques i estructurals úniques. Han despertat interès tecnològic ja que constitueixen una subclasse dels polioxometal·lats (POMs), una gran família de sistemes moleculars inorgànics pels quals ja existeixen aplicacions en camps com la medicina i la catàlisi, entre altres. També s’estan trobant potencials aplicacions per als POVs en una gran varietat d’àrees com l’enginyeria de materials, l’emmagatzematge d’informació i energia i el magnetisme molecular. Aquesta tesi doctoral té com a objectiu principal ampliar el coneixement sobre molècules i dispositius prometedors per a la tecnologia punta. Es basa en un treball computacional realitzat sobre una sèrie de sistemes de POVs dels quals es disposa de dades experimentals. El primer bloc de resultats es centra en la conductivitat de dos tipus de POVs: un derivat del clàssic V6O19, amb tots els àtoms de vanadi inicialment oxidats, i l’altre és I@V18O42, que de forma natural presenta electrons metàl·lics de valència no aparellats. El segon bloc de resultats està dedicat a l’estudi en profunditat de l’estructura electrònica i el complex magnetisme de diversos sistemes ‘host-guest’ basats en l’arquitectura del V22O54.Nuevas aplicaciones tecnológicas para la electrónica están siendo investigadas por la comunidad científica. Tienen como objetivo cubrir las nuevas demandas de sistemas electrónicos más pequeños y potentes, como ordenadores o teléfonos móviles, presentes en nuestra vida diaria. Entre la gran variedad de materiales candidatos que se están desarrollando para estos fines, los polioxovanadatos (POVs) constituyen una familia prometedora por sus características químicas y estructurales únicas. Han despertado interés tecnológico ya que constituyen una subclase de los polioxometalatos (POMs), una gran familia de sistemas moleculares inorgánicos para los que ya existen aplicaciones reales en campos como la medicina y la catálisis, entre otros. También se están encontrando potenciales aplicaciones para los POVs en una gran variedad de áreas como la ingeniería de materiales, el almacenamiento de información y energía y el magnetismo molecular. Esta tesis doctoral tiene como objetivo principal ampliar el conocimiento sobre moléculas y dispositivos prometedores para la tecnología punta. Se basa en un trabajo computacional realizado sobre una serie de sistemas de POVs para de los que se dispone de datos experimentales. El primer bloque de resultados se centra en la conductividad de dos tipos de POVs: uno derivado del clásico V6O19, inicialmente con todos los átomos de vanadio oxidados, y el otro es I@V18O42, que de forma natural presenta electrones metálicos de valencia no apareados. El segundo bloque de resultados está dedicado al estudio en profundidad de la estructura electrónica y el complejo magnetismo de varios sistemas ‘host-guest’ basados en la arquitectura de V22O54.
New technological applications for electronics are being investigated by a large and very active scientific community. These are aimed at covering the new demands for smaller, more powerful electronic systems present in our daily lives, such as computers or mobile phones. Among the great variety of candidate materials being developed for these goals, polyoxovanadates (POVs) constitute a promising family because of their unique chemical and structural characteristics. They have awakened technological interest as they constitute a subclass of polyoxometalates (POMs), a large family of molecular inorganic systems, that have found their way into real-world applications in fields as medicine and catalysis, among others. The POVs are also finding potential applications in a range of areas such as materials engineering, information and energy storage, and molecular magnetism. This Ph.D. thesis is first and foremost aimed at enlarging the knowledge on promising molecules and devices for cutting-edge technology. It is based on computational work done on a series of POV systems for which experimental data is available. It first puts the focus on the conductivity of two POV types: one derived from the classical V6O19, with initially completely oxidized vanadium atoms, and the other is I@V18O42, which naturally features unpaired valence metal electrons. The second part is devoted to the in-depth study of the electronic structure and complex magnetism of several host-guest systems based on the V22O54 architecture.
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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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Engin, Tahir. "Structural, magnetic and electron transport properties of mixed metal sulphides." Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2059.
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The construction of cells that enables the electrical resistance of a material to be measured simultaneously with the collection of powder neutron diffraction data at a range of temperatures (4.2 :5 TIK:5 1000) is described. The cells have been used to investigate the origin of the anomalous electron-transport properties of the ternary sulphides, TICu6.ssS4, BaCu4S3 and CuFeS2. Data for TICu6.ssS4 reveal that the anomaly observed at 255 K is associated with a structural change from P41n to 141m on cooling due to a distortion involving a doubling of the e-axis of the unit cell. There,are .~/ two resistance anomalies observed in BaCu4S3. The first at 523 K is associated' with a phase transition from a two-phase mixture (Pllma + Cmem) to a Cmem phase, whilst the second anomaly can be correlated with the decomposition of the 'sample at 923 K. Variable temperature powder neutron diffraction reveals that CuFeS2 adopts a tetragonal antiferromagnetically ordered structure up to 748 K, above which it consists of a mixture of two phases until TN = 823 K, where a loss of magnetic order is coincident with a transformation to a cubic structure. Resistance anomalies are observed at each of those temperatures. A new family of vanadium-substituted chromium sulphides (VxCr2-xS3, 0 < x < 2) has been prepared and characterized by powder X-ray and neutron diffraction, SQUID magnetometry, electrical resistivity, and Seebeck coefficient measurements. Vanadium substitution leads to a single-phase region with a rhombohedral Cr2S3 structure over the composition range 0.0 < x:5 0.75, while at higher vanadium contents (1.6 :5 x < 2.0) a second single-phase region, in which materials adopt a cation-deficient Cr3S4 structure, is observed. Materials with the Cr2S3 structure all exhibit semiconducting behavior whilst those adopting Cr3S4-type structure exhibit metallic behavior. Materials in both single phase regions undergo a magnetic ordering transition at temperatures in the range 90 - 118 K. Materials with the Cr2S3 structure undergo a transition to a ferrimagnetic state, the nature of which has been determined by low-temperature neutron diffraction measurements. Structural studies of the mixed-metal sulphides, FexMnl_xS (0 :5 x :5 0.4) were performed using powder neutron diffraction. Rietveld refinements show that all samples adopt a cubic rock-salt structure (F'm3m) at room temperature. The Feo.2Mno.sS sample is essentially pure phase whilst materials with higher Fe content contain 3CFe7SS (21.3% in Feo.4Mno.6S). Low-temperature neutron diffraction reveals that all materials are magnetically ordered at temperatures in the range 180 - 185 K, below Which they show a structural distortion. The magnetic structure consists of ferromagnetically aligned layers, with antiferromagnetic coupling of adjacent layers. Electron-transport property measurements reveal that all the samples are Arrhenius semiconductors with activation energies that decrease with increasing Fe content.
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Nguyen, Paul Phong. "Magnetic, DC transport, and microwave properties of high temperature superconductors." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/38023.
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Belk, Nathan. "Electronic transport and magnetic properties of disordered high-Tc materials." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10745.
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Galdi, Alice. "Magnetic orbital and transport properties in LaMnO3 based based heterostructures." Doctoral thesis, Universita degli studi di Salerno, 2011. http://hdl.handle.net/10556/177.
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2009 - 2010This thesis work deals with the magnetic, orbital and transport properties of (LaMnO3)2N(SrMnO3)N digital superlattices and of LaxMnO3-d thin films, both deposited by molecular beam epitaxy (MBE) technique on SrTiO3 substrates. The (LaMnO3)2N(SrMnO3)N digital superlattices represent the new kind of heterostructure, actually under intensive study, composed by an integer number of unit cells, where electronic reconstruction effects at the (clean) interface are expected. In the first part of the thesis work, optical lithography techniques and different deposition techniques are employed in order to perform transport measurement in current perpendicular to plane (CPP) configuration and field effect measurements. The CPP technique would allow to gain more information respect to the in-plane measurements as the ones used in the first part of the thesis. Field effect has been widely investigated in manganite (especially LMO-based) systems, as it represents a method to tune the carrier density, and in order to engineer all oxide field effect devices. The results of the optimization of such techniques, together with the optimization of the materials needed as base electrode, side and gate insulators and top electrode is reported. In the second part of the thesis, both LaMnO3-based systems were studied by traditional techniques (transport measurements, SQUID magnetometer) and soft X-ray absorption and emission techniques by synchrotron radiation. Collecting the data from different measurement techniques, precious information about ferromagnetism, antiferromagnetism and orbital ordering is obtained. [edited by author]
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Shil, Suranjan. "Theoritical investigation of magnetic and electrical transport properties of molecules and radicals." Thesis, University of North Bengal, 2013. http://hdl.handle.net/123456789/1503.
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Haque, Md Firoze H. "Single-electron transport spectroscopy studies of magnetic molecules and nanoparticles." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4914.
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Magnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles are found to behave ferromagnetically for diameters below a few nanometers. Some of these manifestations are still intriguing, and novel research approaches are necessary to advance towards a more complete understanding of these exciting nanoscale systems. In particular, the ability to study an isolated individual nanoscale system (i.e just one molecule or nanoparticle) is both challenging technologically and fundamentally essential. It is expected that accessing to the energy landscape of an isolated molecule/nanoparticle will allow unprecedented knowledge of the basic properties that are usually masked by collective phenomena when the systems are found in large ensembles or in their crystal form. Several approaches to this problem are currently under development by a number of research groups. For instance, some groups are developing deposition techniques to create patterned thin films of isolated magnetic nanoparticles and molecular magnets by means of optical lithography, low-energy laser ablation, or pulsed-laser evaporation or specific chemical functionalization of metallic surfaces with special molecular ligands. However, it is still a challenge to access the properties of an individual molecule or nanoparticle within a film or substrate. I have studied molecular nanomagnets and ferromagnetic noble metal nanoparticles by means of a novel experimental approach that mixes the chemical functionalization of nano-systems with the use of single-electron transistors (SETs). I have observed the Coulomb-blockade single-electron transport response through magnetic gold nanoparticles and single-molecule magnet. In particular, Coulomb-blockade response of a Mn[sub4]-based SET device recorded at 240 mK revealed the appearance of two diamonds (two charge states) with a clear switch between one and the other is indicative of a conformational switching of the molecule between two different states. The excitations inside the diamonds move with magnetic field. The curvature of the excitations and the fact of having them not going down to zero energy for zero magnetic field, indicated the presence of magnetic anisotropy (zero-field splitting) in the molecule. In addition, the high magnetic field slope of the excitations indicates that transitions between charge states differ by a net spin value equal to 9 (|ΔS| = 9), as expected from the behavior of Mn4 molecules in their crystalline form. Anticrossings between different excitations are indicative of quantum superpositions of the molecular states, which are observed for the first time in transport measurements through and individual SMM.ID: 029810145; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 92-98).
Ph.D.
Doctorate
Physics
Sciences
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SILVA, VICTOR LOPES DA. "MAGNETIC, TRANSPORT AND EMERGENT PROPERTIES IN NANOSCOPIC AND STRONGLY CORRELATED SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36045@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
PROGRAMA DE EXCELENCIA ACADEMICA
Esta tese investiga as propriedades eletrônicas de sistemas nanoscópicos com interações de muitos corpos, dando origem ao efeito Kondo. Primeiramente estudamos a transição SU(4)-SU(2) devido a um campo magnético externo e as propriedades de filtro de spin de um nanossistema de dois pontos quânticos capacitivamente acoplados. A transição é caracterizada pela diferença entre as polarizações de spin da ocupação eletrônica nos dois pontos quânticos, como uma função do potencial de porta aplicado sobre os pontos quânticos. Apesar do fato de que o campo magnético externo quebra a simetria SU(4) do Hamiltoniano, o estado fundamental a preserva, como uma propriedade emergente, na região do espaço de parâmetros onde os elétrons não estão polarizados. As propriedades de filtro de spin devido à população eletrônica spin polarizada nos pontos quânticos também é discutida. Estas propriedades são estudadas usando o formalismo dos operadores de projeção, que descreve de forma muito acurada a física associada ao estado fundamental dos sistemas Kondo. No capítulo subsequente, analisamos os efeitos da interação spin-órbita num ponto quântico conectado a contatos, representados pelo modelo da impureza de Anderson no efeito Kondo. Contrariamente ao resultado prévio de vários outros autores, nós mostramos que a interação spin-órbita reduz exponencialmente a temperatura Kondo enquanto a ação da interação no próprio ponto quântico pode ser um mecanismo de destruição do regime Kondo, conforme quebra a simetria SU(2). Usando o modelo de Anderson com acoplamento spin-órbita nós propomos um transistor de spin feito de um ponto quântico conectado a uma nanofaixa submetida à interação spin-órbita Rashba, depositada sobre um substrato ferromagnético. O ponto quântico também é conectado a dois contatos metálicos laterais, através do qual a corrente flui ao longo do sistema. A interação spin-órbita Rashba cria um mecanismo de inversão do spin no ponto quântico. Nós mostramos que o sistema é capaz de operar como um transistor de spin.
This thesis investigates the electronic properties of nanoscopic systems under the presence of many body interactions, given rise to the Kondo effect. Firstly we studied the SU(4)-SU(2) crossover driven by an external magnetic field and the spin-filter properties of a capacitively coupled double quantum dot nanosystem. The crossover is characterized by the difference between the spin polarization of the electronic occupation at the double quantum dot, as a function of the gate potential applied to the quantum dots. Despite the fact that the external magnetic field breaks the SU(4) symmetry of the Hamiltonian, the ground state preserves it, as an emergent property, in a region in the parameter space where the electron are not polarized. The spinfilter properties due the spin polarized electronic population at the dots is also discussed. These properties are studied using the projector projection operator approach, which describes very accurately the physics associated to the ground state of Kondo systems. In a subsequent chapter, we analyze the effect of the spin-orbit interaction in a quantum dot connected to leads, represented by the Anderson impurity model on the Kondo effect. Contrary to several other authors previous results, we show that the Rashba spin-orbit interaction exponentially reduces the Kondo temperature while the action of the interaction on the quantum dot itself could be a mechanism of destroying the Kondo regime, as it breaks SU(2) symmetry. Using the Anderson model with spin-orbit coupling we propose a spin transistor device made of a quantum dot connected to a Rashba spinorbit interacting nanoribbon, deposited on a ferromagnetic substrate. The quantum dot is also connected to two lateral metallic contacts, through which the current flows along the system. The Rashba spin-orbit interaction creates a spin-flip mechanism at the quantum dot. We show that the system is capable of operating as a spin-transistor.
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Sokolov, Dmitriy A. "Effect of pressure on transport and magnetic properties of layered manganites." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/14442.
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Zayer, Nadhum Kadhum. "Magnetic and transport properties of sputtered iron-aluminium films under vacuum." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/21526.
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Sputter deposition is one of the vapour quenching methods used to produce alloying compounds in thin film form. The alloying compounds produced by this method have a chemically homogeneous, non-equilibrium structure which is dill'erent from that of alloys produced by solid quenching, liquid quenching, or mechanical alloying methods. In the present investigation the Fe 1-:x.A1x alloy thin films were prepared using multisource magnetron sputtering. The samples were deposited onto a water cooled substrate and their thickness was kept constant at t- 300nm. To investigate the effect of the deposition parameters on the properties of the films, the samples were deposited at various argon gas pressures PAr I, 3, or 4 mtorr. The effect of gas pressure is consistent with the thermalization of the deposited material by collisions with gas atoms in the chamber. The composition range of the samples varied from pure iron to pure aluminium. The composition, structure and morphology of the films was obtained using Transmission Electron Microscopy (TEM). X-ray diffraction patterns were also used to obtain the structure of the films. Structure analysis showed that a bcc crystalline structure was obtained in samples of composition range x= 0 to - 50%, an amorphous structure in samples of composition range x- 55% to - 83%, and a fcc crystalline structure in samples of composition range x- 85% to 100%. These composition ranges are affected by altering the deposition gas pressure. The morphology of the deposited films was observed to be affected by the deposition gas pressure. The samples deposited at low gas pressure Par=1 mtorr consist of a fibrous structure with densely packed boundaries, while the samples deposited at high gas pressure Par=4 mtorr consist of columnar structures separated by open boundaries. Room temperature resistivity measurements show a drop in resistivity in the composition range x- 30% to 50%. This drop is thought to be due to the formation of chemically ordered Fe3Al and FeAI compounds. Also the resistivity increases with increasing argon gas pressure. The effect of altering the argon gas pressure is to change the morphology of these alloys, and this has a significant effect on the magnetic properties. The effect of annealing on the magnetisation and morphology was also studied in the samples. A low temperature resistivity measurement system was constructed. A closed cycle helium refrigerator, which provided a working temperature range of T= l5°K to 3000K was used for the cooling process. The resistivity measurements revealed three distinct characteristics dependent on composition :- 1. x= 0 to 46%: The samples in this range exhibit a metallic behaviour, with the samples in the composition range x= 27% to 46% showing a resistivity minimum at low temperature which is thought to be due to spin glass formation. 2. x= 48% to 83%: These samples have a semiconductor or metallic glass-like behaviour. 3. x= 85% to 100%: These samples show a metallic behaviour. The above properties are associated with the change in the structure of the fiIrns as the composition varies. A computer controlled AC susceptometer was designed and constructed to measure the AC susceptibility of the samples in the temperature range T= 20 OK to T= 300 OK. A closed cycle helium refrigerator was used to provide the cooling process. The AC susceptibility measurements for the samples with resistivity minima show a sharp peak at low temperature which confirms the presence of spin glass in these samples at low temperature. The results of magnetic and transport properties can be related to the structure and morphology of the filrns. The results have been compared with those obtained from bulk samples with the same composition.
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Sarbadhikary, Prodipta. "Magnetic and transport properties of spin polarized molecular systems: theoretical perspective." Thesis, University of North Bengal, 2021. http://ir.nbu.ac.in/handle/123456789/4668.
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Korneta, Oleksandr B. "A systematic study of transport, magnetic and thermal properties of layered iridates." UKnowledge, 2012. http://uknowledge.uky.edu/physastron_etds/2.
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A unique feature of the 5d-iridates is that the spin-orbit interaction (SOI) and Coulomb interactions U are of comparable strength and therefore compete vigorously. The relative strength of these interactions stabilizes new exotic ground states that provide a fertile ground for studying new physics. SOI is proportional to Z^4 (Z is the atomic number), and it is now recognized that strong SOI can drive novel narrow-gap insulating states in heavy transition metal oxides such as iridates. Indeed, strong SOI necessarily introduces strong lattice degrees of freedom that become critical to new physics in the iridates. This dissertation thoroughly examines a wide array of newly observed novel phenomena induced by adjusting the relative strengths of U and SOI interactions via slight chemical doping and application of hydrostatic pressure in the layered iridates, particularly, BaIrO3 and Sr2IrO4.
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Ali, Zeeshan. "GROWTH, TRANSPORT, AND MAGNETIC PROPERTIES OF OBLIQUE-ANGLE-DEPOSITED PERMALLOY THIN FILMS." Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami1533323927495291.
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Aeschlimann, Raphaël. "Magnetic and transport properties of rare-earth titanate thin films and heterostructures." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS142.
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Les oxydes de métaux de transitions possèdent une large gamme de fonctionnalités (supraconductivité, magnétisme, ferroélectricité, multiferroicité) découlant de l’interaction d’effets structuraux et de corrélations fortes. De plus, des travaux récents ont mis en lumière une physique propre à leurs interfaces, incluant de la supraconductivité ainsi que de la conductivité classique dans le système bidimensionnel (2DES) créé à l’interface de deux isolants de bande, LaAlO₃ et SrTiO₃. Malgré cela pour couvrir l’immense potentiel des interfaces d’oxydes et leur phases électroniques sans précédent, il est nécessaire de combiner des oxydes plus fortement corrélés. Cette thèse à la croisée des chemins entre la physique des électrons fortement corrélés, du magnétisme et de la spintronique a pour but de combiner les instabilités magnétique et électronique pour créer de nouvelles phases électronique contrôlable par stimulus externe. Pour cela nous nous sommes intéressés à la famille relativement inexplorée des titanates de terres rares dont l’ordre magnétique ferro ou antiferro est contrôlé par la taille de la terre rare. Contrairement aux travaux existants, nous nous somme concentrés sur les membres ferrimagnétiques de la famille et leur intégration dans des 2DES. Cette thèse se développera autour de deux axes principaux. Dans un premier temps nous avons étudié plusieurs membres de la famille des titanates de terres rares sous la forme de couches minces épitaxiées. Nous avons aussi mis en évidence la présence d’une couche morte magnétiquement active à la surface de ces échantillons et expliqué sa présence par une suroxydation des ions titane de la surface. Nous avons aussi étudié la présence inattendue d’un moment orbital porté par le titane dans certains des composés étudiés et l’avons corrélé à leur structure magnétique non-colinéaire en conjonction avec un gradient structural observé en microscopie électronique en transmission. Dans un second temps nous avons combiné DyTiO₃ avec SrTiO₃ pour obtenir une interface conductrice possédant des propriétés de magnetrotransport complexes que nous avons interprété avec l’aide d’un modèle faisant intervenir le couplage spin-orbite ainsi qu’un magnétisme induitTransition metal oxides possess a broad range of functionalities (superconductivity, magnetism, ferroelectricity, multiferroicity) stemming from the interplay between structural effects and electronic correlations. Recent work has revealed exciting physics at their interfaces, including conductivity and superconductivity in the two-dimensional electron system (2DES) that forms at the interface between two band insulators, LaAlO₃ and SrTiO₃. However, to embrace the immense potential of oxide interfaces and unveil unprecedented electronic phases, combining insulators with stronger electronic correlations is necessary. At the crossroad between strongly correlated electron physics, magnetism and spintronics, the present thesis project aims to harness electronic and magnetic instabilities in correlated oxides to craft new electronic phases controllable by external stimuli. We investigated rareearth titanates RTiO₃, a relatively unexplored family of Mott insulating perovskites with a crossover between antiferromagnetic and ferromagnetic orders upon changing the rare-earth size. Contrary to most previous works, we focused on ferromagnetic compounds, and their integration in 2DES. The thesis developed along two main axes. First, we explored several members of the rare-earth titanates family in epitaxial thin film form. We highlighted the presence of a magnetically active dead layer at the surface of thin films and established its origin as due to the overoxidation of titanium ions. We also studied the presence of an unexpected orbital moment carried by the titanium in some compounds, and discussed it in the light of the non-collinear spin arrangement promoted by the rare-earth orbital moment and of a structural gradient evidenced by transmission electron microscopy. In a second stage, we combined DyTiO₃ with SrTiO₃ to stabilize a conducting interface with puzzling magnetotransport properties that we interpreted with a model involving spin-orbit coupling as well as induced magnetism
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Sankar, Sandrawattie. "Correlation of microstructural, magnetic, and transport properties of composite metal-insulator films /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9963657.
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Pandey, Sudip. "MAGNETIC, TRANSPORT, AND MAGNETOCALORIC PROPERTIES OF BORON DOPED Ni-Mn-In ALLOYS." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1754.
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The impact of B substitution in Ni50Mn35In15-xBx Heusler alloys with x = (0, 0.5, 0.75, 1, 1.1 1.5, and 2) on the structural, magnetic, transport, and parameters of magnetocaloric effect has been studied by means of room temperature XRD-diffraction, differential scanning calorimetry (DSC), and thermomagnetic measurements (in a magnetic field up to 5 T and temperature interval 5-400 K). Direct adiabatic temperature (ΔTAD) measurements have been carried out for an applied magnetic field change (ΔH) of 1.8 T. The partial substitution of In by B in Ni50Mn35In15-xBx Heusler alloys induced a non-linear temperature shift of the magnetostructural transition while Curie temperature (TC) was found to be nearly constant (TC ~ 320 K) for all compounds. The transition temperatures (T-x) phase diagram has been constructed for H = 0.005 T. The MCE parameters were found to be larger or comparable to parameters observed in other MCE materials, such as Ni50Mn34.8In14.2B and Ni50Mn35In14X (X=In, Al, and Ge) Heusler alloys. It has been demonstrated that the martensitic transformation temperature and the corresponding ∆SM can be tuned through a slight variation in composition of B in NiMnInB alloys. A magnetoresistance associated with martensitic transformation was found to be -60% for x = 0.75 at T = 240 K for a magnetic field change of 5 T. The maximum absolute value of ΔTAD = 2.5 K was observed at the magnetostructural transition for Ni50Mn35In14.5B0.5. The roles of the magnetic and structural changes on the transition temperatures are discussed.
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Lampert, Lester Florian. "High-Quality Chemical Vapor Deposition Graphene-Based Spin Transport Channels." PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3327.
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Spintronics reaches beyond typical charge-based information storage technologies by utilizing an addressable degree of freedom for electron manipulation, the electron spin polarization. With mounting experimental data and improved theoretical understanding of spin manipulation, spintronics has become a potential alternative to charge-based technologies. However, for a long time, spintronics was not thought to be feasible without the ability to electrostatically control spin conductance at room temperature. Only recently, graphene, a 2D honeycomb crystalline allotrope of carbon only one atom thick, was identified because of its predicted, long spin coherence length and experimentally realized electrostatic gate tunability. However, there exist several challenges with graphene spintronics implementation including weak spin-orbit coupling that provides excellent spin transfer yet prevents charge to spin current conversion, and a conductivity mismatch due to the large difference in carrier density between graphene and a ferromagnet (FM) that must be mitigated by use of a tunnel barrier contact. Additionally, the usage of graphene produced via CVD methods amenable to semiconductor industry in conjunction with graphene spin valve fabrication must be explored in order to promote implementation of graphene-based spintronics. Despite advances in the area of graphene-based spintronics, there is a lack of understanding regarding the coupling of industry-amenable techniques for both graphene synthesis and lateral spin valve fabrication. In order to make any impact on the application of graphene spintronics in industry, it is critical to demonstrate wafer-scale graphene spin devices enabled by wafer-scale graphene synthesis, which utilizes thin film, wafer-supported CVD growth methods.
In this work, high-quality graphene was synthesized using a vertical cold-wall furnace and catalyst confinement on both SiO2/Si and C-plane sapphire wafers and the implementation of the as-grown graphene for fabrication of graphene-based non-local spin valves was examined. Optimized CVD graphene was demonstrated to have ID/G ≈ 0.04 and I2D/G ≈ 2.3 across a 2" diameter graphene film with excellent continuity and uniformity. Since high-quality, large-area, and continuous CVD graphene was grown, it enabled the fabrication of large device arrays with 40 individually addressable non-local spin valves exhibiting 83% yield. Using these arrays, the effects of channel width and length, ferromagnetic-tunnel barrier width, tunnel barrier thickness, and level of oxidation for Ti-based tunnel barrier contacts were elucidated. Non-local, in-plane magnetic sweeps resulted in high signal-to-noise ratios with measured ΔRNL across the as-fabricated arrays as high as 12 Ω with channel lengths up to 2 µm. In addition to in-plane magnetic field spin signal values, vertical magnetic field precession Hanle effect measurements were conducted. From this, spin transport properties were extracted including: spin polarization efficiency, coherence lifetime, and coherence distance.
The evaluation of industry-amenable production methods of both high-quality graphene and lateral graphene non-local spin valves are the first steps toward promoting the feasibility of graphene as a lateral spin transport interconnect material in future spintronics applications. By addressing issues using a holistic approach, from graphene synthesis to spin transport implementation, it is possible to begin assessment of the challenges involved for graphene spintronics.
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Mustafa, Luqman [Verfasser], and Bernhard [Akademischer Betreuer] Keimer. "Magnetic and transport properties of YBa2Cu3O7 - La0.7Ca0.3MnO3 heterostructures / Luqman Mustafa ; Betreuer: Bernhard Keimer." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2016. http://d-nb.info/1124000062/34.
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Rushforth, Andrew William. "The transport properties of two dimensional electron gases in spatially random magnetic fields." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342029.
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Williams, Benjamin Heathcote. "Nano- and micro-scale techniques for electrical transport measurements." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:09c73d9f-b68d-4f06-9ffe-cbb29d200809.
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This thesis outlines the development of two new techniques that exploit very small structures, on the micro- and nano-scale, to enable innovative electrical transport measurements on a variety of materials of current interest in condensed matter physics. The first technique aims to apply the versatility of electron-beam lithography for micro-fabrication of patterned electronic circuitry to the problem of performing transport experiments on individual crystallites taken from a typical powder sample. We show that these small samples, tens of microns in size, are actually often very high quality single crystals and can be exploited for measurements of electrical transport in materials of which no larger crystals are available. By way of demonstration, we present the results of preliminary transport measurements on a crystallite of the layered oxide chalcogenide Sr2MnO2Cu1.5Se2. We report a phase transition in the resistivity at 213K which may correspond to the onset of previously reported short-range order in copper and vacancy sites in the Cu1.5Se2 planes. The second technique is designed to investigate the topological protection of surface transport in 3-D topological insulators. We decorate the surfaces of single-crystal samples with two different species from a well-characterised family of single-molecule magnets. The two coatings have an electrostatically identical influence on the sample surface, but differ in that one species carries a spin and the other is spinless. The spinless molecule acts as a control, to allow us to cleanly determine the influence of the magnetic component of a scattering potential on transport in the surface. With this technique we investigate proposed topological Kondo insulator SmB6. We find that the surface state dominates low-temperature transport and demonstrate that the momentum relaxation is very sensitive to a spin degree of freedom in the scatterer, in keeping with expectations of a topological insulator.
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Farhoudi, Mohammad Mehdi. "Studies of structures, transport and magnetic properties of doped novel three-dimensional perovskite compounds." Institute for Superconducting and Electronic Materials - Faculty of Engineering, 2009. http://ro.uow.edu.au/theses/3047.
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Perovskite oxide compounds have generated a great amount of interest over the past twenty years, as they exhibit exotic magnetic, electric, and magnetoelectric properties, which, apart from their intrinsic interest, would have a wide range of applications in industry, with special utilization in the engineering of data storage devices.Starting with a general definition of the perovskite structure of ABO3 materials, the magnetic and transport properties of cobalt and manganese based compounds are reviewed. The objective of this thesis is focused on the investigation of the structures, and the magnetic and transport properties of some typical cobalt or manganese based three-dimensional perovskite compounds doped with various elements.Polycrystalline samples of RE1-xSrxCoO3 (RE = Gd, Nd, Ho, Y, and Dy), REMnxCo1-xO3 (RE = Gd and Ho), and La0.33Sr0.66Fe1-xCrxO3 were fabricated and characterized in detail using X-ray diffraction, Rietveld structural refinement, magnetic and transport measurements, X-ray absorption near-edge (XANES) spectroscopy, and far-infrared (FIR) spectroscopy.Perovskite GdCo1-xMnxO3 (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8) compounds were prepared by solid-state reaction. Structures were characterized using X-ray diffraction and the Rietveld refinement method. The compounds crystallized in the orthorhombic structure with Plmn space group. Crystal lattice parameters constants decreased with increasing Mn doping level. DC magnetization and ac susceptibility were studied over a wide temperature range and different frequencies. A typical spin glass state was observed in all samples around the same temperature of 122 K, where the compounds changed from the paramagnetic to the ferromagnetic state. For x = 0.5, secondary transitions were observed both in dc and in ac measurements, which were independent of the frequency, but depended on the doping level. The valences of Co and Mn were estimated with possible spin states.The structures, magnetism, giant magnetoresistance, and spin and valence states of Co ions were investigated in perovskite Gd1-xSrxCoO3 (x = 0-0.5) compounds synthesized by a solid state reaction method. Results showed that all the samples are ferromagnetic around 150 K, and the magnetization and coercive field increase with the Sr doping level. A spin glass state was observed. Furthermore, the resistivity drops systematically with x. Giant magnetoresistance of over 60% was observed for the Gd0.5Sr0.5CoO3 sample. Spin state assessment indicates that the Co3+ and Co4+ ions are present in intermediate and high spin states.Polycrystalline perovskites compounds HoMn1-xCoxO3 (x = 0-0.8) were prepared by conventional solid-state reaction. Rietveld refinement indicated that, instead of a hexagonal structure with P63cm symmetry for HoMnO3, the compounds doped with Co crystallized in the GdFeO3-type orthorhombic structure containing distorted (Co/Mn)O6 octahedral. The dc magnetization was measured in fields up to 5 T over a wide temperature range from 350 K down to 5 K. It was found that the system gradually changed from paramagnetic for x = 0 to ferromagnetic with a Curie temperature, TC, of 90 K for x = 0.5, then to paramagnetic again for x = 0.8. X-ray absorption near-edge spectra (XANES) were collected to determine the valences of both Co and Mn ions. The results showed that Co and Mn were present mainly as mixed valences of Co2+ + Co3+, Mn4+ + Mn3+, Co3+ +Co4+, and Mn4+, depending on the value of x. When the XANES results were combined with Curie-Weiss fitting, it was found that both Mn4+ and Co3+ were present as high spin states for x > 0.2, whereas, Co4+ appeared in either intermediate or high spin states, closely corresponding to the lattice variations along the (010) direction. HoMn1-xCoxO3 (x = 0-0.8) compounds were also studied by far-infrared (FIR) spectroscopy in order to gain information on the infrared active phonon modes. The data indicated that phonon modes significantly changed with increasing cobalt doping level. Four main bands were assigned as external, torsional, bending, and stretching bands. The external vibration energy remained the same at 1190 cm-1 for Co doping with x < 0.5 and shifted to higher energy for x > 0 5. The torsional and bending bands exhibited splitting. The stretching band is at 600 cm-1 for all samples, but the bandwidth is reduced as Co doping is increased. The transmission spectrum of HoMn4/5Co1/5O3 was analyzed to obtain the spectrum of the optical density. The minimum number of oscillators to obtain a reliable fit is 5, using a sum of non-interacting harmonic oscillators.Cr doping effects on the crystal structures and magnetic properties for La1/3Sr2/3Fe1-xCrxO3 were studied in this work. It was observed that single phase samples with the cubic crystal structure can only form within a narrow solubility range. Magnetic measurements showed that the resulting compounds are magnetic insulators.
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Every, Hayley A. (Hayley Ann) 1973. "An NMR diffusion study of the transport properties in novel electrolytes." Monash University, Dept. of Materials Engineering, 2001. http://arrow.monash.edu.au/hdl/1959.1/8796.
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Sun, Yongke. "Theoretical studies of the electronic, magneto-optical, and transport properties of diluted magnetic semiconductors." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011604.
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Cachia, S. H. "Molecular dynamics simulations of water transport properties and magnetic resonance relaxation in cement nanopores." Thesis, University of Surrey, 2016. http://epubs.surrey.ac.uk/812105/.
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Water transport properties in cement are important for the cement industry. At the nanoscale, a nondestructive experimental method, 1 H nuclear magnetic resonance [NMR] relaxometry, can be used to quantify these properties. However, recent results have proven difficult to reconcile with current understanding of cement. The purpose of this work is to use Molecular Dynamics [MD] simulations to try and better understand water in cement and hence better interpret some of the NMR data. In particular, MD simulations are used to investigate water dynamics in two sizes of nanopores in analogues of calcium-silicate-hydrate [C-S-H], which is the active phase of cement paste. These pores are gel pores (3-5 nm) and interlayer spaces (1 nm). First, a bulk water system is studied and the water diffusion coefficient and NMR relax ation times are calculated. The results are compared to literature values and used to validate the methods. Then, different C-S-H analogues based on SiO 2] α -quartz crystal, tobermorite 11 ̊ A and modified tobermorite 14 ̊ A are presented. Two different sets of interatomic poten tials are used for these model simulations: CLAY FF+SPC/E and Freeman+TIP4P. These simulations are then compared. A model called MD4 which is based on modified tobermorite 14 ̊ A and using CLAY FF+SPC/E potentials is selected for further work. The density profile of water oxygen in MD4 is used to identify four water layers with different properties in the gel pore (L1, L2, TL and B) and one water layer in the interlayer pore (IL). Diffusivity and desorption analyses are performed on water populations related to these layers. The importance of the calcium ions close to the surface is highlighted. The NMR dipolar correlation function is generated for water using data from the MD4. This function underpins relaxation analysis. These outputs are compared to Korb’s single water layer model of surface NMR relaxation. Korb’s model is not supported by the new data. However, a new relaxation model of surface relaxation that takes into account water in two layers is supported by the data. Exchange is possible between these layers and is important for diffusivity as well as relaxation. Simulations are carried out as a function of temperature and used to calculate water trans- port activation energies in bulk and in MD4. Finally, the analysis of water exchange between the interlayer and gel pores is performed. It is shown that the exchange time in simulations is ≈69000 times smaller than measured experimentally. Some possible failings in the model that would account for this are discussed.
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Zhu, Tiancong. "Tuning the Spin Transport and Magnetic Properties of 2D Materials at the Atomic Scale." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563385375225464.
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Chaudhry, Wahid. "Vertical transport through n-InAs/p-GaSb heterojunctions at high pressures and magnetic fields." Thesis, University of Oxford, 1999. http://ora.ox.ac.uk/objects/uuid:355f36e2-cae2-4dad-8639-ed9f618c98ea.
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The conduction band of InAs lies lower in energy than the GaSb valence band. In order to preserve continuity of the Fermi level across the interface, charge transfer takes place resulting in a confined quasi two dimensional electron gas (2DEG) in the InAs and a confined quasi two dimensional hole gas (2DHG) in the GaSb. This study is an investigation into the vertical transport in an n-InAs/p-GaSb single heterojunction (SHET). Application of a forward bias (InAs negative with respect to GaSb) increases the 2DEG and 2DHG concentrations and, therefore, their confinement energies. Eventually a critical bias is reached where the electron confinement energy moves above the hole confinement energy (the theoretical voltage induced semimetal/semiconductor transition Vc). Any subsequent increase in voltage is expected to result in a current decrease, and a region of negative differential resistance (NDR) should occur. The SHET can be grown with two distinct interface types, 'InSb-like' and 'GaAs-like'. This in turn affects the vertical transport characteristics of each type. Experimental IV traces at various pressures are compared with the corresponding results from sophisticated self-consistent band profile calculations taking into account band mixing effects for the first time through a k.p theory framework. Experimental IV traces of the SHETs under a magnetic field parallel to the interface are also compared with results from calculations that take into account the coupling of the growth and in-plane electron and heavy hole motions. Both sets of analysis support earlier conclusions that NDR occurs after Vc for both interfaces, and that each interface supports a different conduction mechanism. Evidence of multiple phonon processes occurring in both sample types is observed for the first time and is proposed to reconcile the above experimental observations with theory. This data is found to offer explanations for a number of other observations. Field perpendicular to the interface leads to the observation of features beyond the NDR region in both sample types. In samples with an 'InSb-like' interface, applying additional hydrostatic pressure leads to very strong features beyond the main NDR. Through a complex self-consistent decoupled model taking into account electrons and heavy holes, all these features are proposed to be due to a filling of an integer number of Landau levels. The band profile is predicted to alter dramatically at this point. The same model explains the observation of weaker features at 1 bar at high fields (~ 40T). A variation of NDR position is found with a rotation of an-plane field.
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Pu, Yong. "Spin-dependent transport properties of Ga₁₋[subscript]xMn[subscript]xAs ferromagnetic semiconductors." Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=142&did=1874094571&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270493990&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Includes bibliographical references (leaves 122-126). Issued in print and online. Available via ProQuest Digital Dissertations.
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Spivak, Mariano Alejo. "Electronic structure calculations on extended metal atom chains. Insights on structural, magnetic and transport properties." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/399580.
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En aquest treball, es van utilitzar diferents mètodes computacionals per estudiar les propietats de cadenes esteses de metalls de transició (EMACs en anglès). Es va simular la flexibilitat estructural de cadenes de tres àtoms de crom, amb CASSCF/CASPT2 i es van identificar estructures simètriques i asimètriques en un entorn de baixa energia. Basats en aquests resultats, vam realitzar dinàmiques moleculars de primers principis (AIMD) per entendre l'efecte de l'energia tèrmica i com aquesta modifica la proporció d'estructures. També es van estudiar els enllaços metall-metall en compostos de crom, utilitzant el model d'ordre d'enllaç efectiu (EBO) amb els números d'ocupació naturals de la funció d'ona CASSCF. Es van calcular constants d'acoblament magnètic per a compostos bimetàl·lics i EMACs de níquel mitjançant dues estratègies. MC-PT2 amb espai actiu mínim utilitzant orbitals moleculars millorats a partir d'un càlcul d'estats-mitjanats, i es va utilitzar un mètode nou (MCPDFT) per al magnetisme de EMACs grans, que ha mostrat bons resultats en el compost de cinc níquels. Finalment, estudiem propietats del transport d'electrons per dos EMACs de ruteni. Proposem l'ús d'un elèctrode gate metàl·lic per modular els nivells moleculars dels compostos i obtenir espècies redox actives. També utilitzem un mètode químicament més intuïtiu, que proposa crear parells iònics dins de la cel·la.En este trabajo, se utilizaron diferentes métodos computacionales para estudiar las propiedades de cadenas extendidas de metales de transición (EMACs en inglés). Se simuló la flexibilidad estructural de cadenas de tres átomos de cromo, con CASSCF/CASPT2 y se identificaron estructuras simétricas y asimétricas en un entorno de baja energía. Basados en estos resultados, realizamos dinámicas moleculares de primeros principios (AIMD) para entender el efecto de la energía térmica y como ésta modifica la proporción de estructuras. También se estudiaron los enlaces metal-metal en compuestos de cromo, utilizando el modelo de orden de enlace efectivo (EBO) con los números de ocupación naturales de la función de onda CASSCF. Se calcularon constantes de acoplamiento magnético para compuestos bimetálicos y EMACs de níquel mediante dos estrategias. MC-PT2 con espacio activo mínimo utilizando orbitales moleculares mejorados a partir de un cálculo de estados-promediados, y se utilizó un método nuevo (MCPDFT) para el magnetismo de EMACs grandes, que ha mostrado buenos resultados en el compuesto de cinco níqueles. Finalmente, estudiamos propiedades del transporte de electrones para dos EMACs de rutenio. Proponemos el uso de un electrodo gate metálico para modular los niveles moleculares de los compuestos y obtener especies redox activas. También utilizamos un método químicamente más intuitivo, que propone crear pares iónicos dentro de la celda.
In this work we use different computational methods in the study of the properties of Extended Metal Atom Chains. The structural flexibility of trichromium chains has been simulated with CASSCF/CASPT2 and symmetric and asymmetric structures were identified in an extremely flat energy landscape. Based on these results, Ab initio molecular dynamic simulations were performed to understand how the thermal energy modifies the proportion of cited structures. In addition, the metal-metal bonding of chromium compounds was characterized using the Effective Bond Order (EBO) model with the natural occupation numbers of the CASSCF wave function. Furthermore, magnetic coupling constants were computed for nickel bimetallic and EMACs compounds, using two different approaches. Minimal active space MC-PT2 was performed with improved molecular orbitals based on state-average calculations, and a recently developed method (MCPDFT) used for the magnetism of large EMACs, showing good results in the five-nickel compound. Finally, the electron transport properties were simulated for two ruthenium EMACs. We propose the use of a metallic gate electrode to modulate the molecular levels of the compounds and achieve redox active species. In addition, another more chemically intuitive approach was tested, that consist of forming an ionic pair in-situ.
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Das, Supriyo. "Synthesis and structural, magnetic, thermal, and transport properties of several transition metal oxides and arsenides." [Ames, Iowa : Iowa State University], 2010. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3403075.
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Bentien, Anders [Verfasser]. "Transport and magnetic properties of rare-earth containing clathrates and clathrate-like compounds / Anders Bentien." Aachen : Shaker, 2005. http://d-nb.info/1181619599/34.
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Matthes, Patrick [Verfasser], Manfred [Akademischer Betreuer] Albrecht, Manfred [Gutachter] Albrecht, and Sibylle [Gutachter] Gemming. "Magnetic and Magneto-Transport Properties of Hard Magnetic Thin Film Systems / Patrick Matthes ; Gutachter: Manfred Albrecht, Sibylle Gemming ; Betreuer: Manfred Albrecht." Chemnitz : Universitätsbibliothek Chemnitz, 2016. http://d-nb.info/1213814332/34.
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Agbo, Sunday A. "Phase Transitions and Associated Magnetic and Transport Properties in Selected NI-MN-GA based Heusler Alloys." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1595644731616343.
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Spencer, Charles Steven Bolanos. "Helical magnetic structure and transport properties in epitaxial B20 Fe(1−x)Co(x)Ge films." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/20225/.
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We have grown epitaxial single-phase B20 Fe(1−x)Co(x)Ge films on Si (111) substrates films by molecular beam epitaxy. This method is able to produce the whole range of Fe(1−x)Co(x)Ge which are of high quality due to homogeneous layer growth with low surface roughness of 1-2 nm. The films grown are racemic, showing an equal mix of left-handed and right-handed chiral grains, and are strained due the lattice mismatch between the film and substrate. Magnetic measurements showed the FeGe films grown (~ 70 nm thickness) have a saturation moment, Ms = 0.982(7) μB, and ordering temperature, Tc = 280(2) K, both close to bulk value. Ms and Tc were found to decrease monotonically with increasing x and all films were found to have an easy-plane anisotropy. A helical magnetic structure was observed using polarised neutron reflectometry and we found the helix wavelength to vary with composition. A divergence in the wavelength was found at a critical composition xc = 0.5 where a transition from helimagnet to collinear ferromagnet occurred. The temperature dependent resistivity, ρxx(T), was found to be metallic for all compositions and a broad peak with magnetic origin was found to arise for intermediate compositions 0.2 < x < 0.7. The magnetoresistance in Fe(1−x)Co(x)Ge with 0.1 < x < 1 was found to behave similarly to FeGe, however many differences were observed, such as a positive linear magnetoresistance for Fe(0.4)Co(0.6)Ge and a change in conical magnetoresistance scaling beyond Fe(0.5)Co(0.5)Ge. The Hall resistivity showed an increase as well as a sign change in the ordinary Hall effect coefficient, R0, from 0.0122 μΩ cm/T for FeGe to -0.6808 μΩ cm/T for Fe(0.5)Co(0.5)Ge, at 5 K, indicating a large reduction in the carrier concentration and change of carrier type. The anomalous Hall effect was found to increase dramatically on the introduction of Co, increasing by an order of magnitude from FeGe to Fe(0.9)Co(0.1)Ge at 5 K. We find evidence of potential skyrmion structures through the measurement of the topological Hall effect, with features as large as -0.39 μΩ cm for Fe(0.6)Co(0.4)Ge at 5 K. We conclude Fe(1−x)Co(x)Ge is a potential material for further skyrmion study, but direct observation of these topological structures are required to fully attribute the measured effect and progress further.
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俞大風 and Tai-fung Yu. "An analysis of electrical transport and magnetic susceptibility properties of YBa2Cu3O7-[delta] and La2-xSrxCuO4 high Tcsuperconductors." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31238014.
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Lai, Eric Y. T. "Unifying the phase diagrams of the magnetic and transport properties of La¦2¦-[subscript]xSr[subscript]xCuO¦4." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq22337.pdf.
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Lin, Cheng Hung, and 林政宏. "Transport and Magnetic Properties in La1-xCaxMnO3." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/35657603832819964398.
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碩士國立高雄師範大學
物理學系
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The transport and magnetic properties of colossal magnetoresistance materials La1-XCaXMnO3 have been studied by using dc/ac magnetic susceptibility measurement, hysteresis curve measurement, resistivity measurement, specific heat measurement and Hall coefficient measurement.The dc magnetic susceptibilityχ, linear absorption part of ac magnetic susceptibilityχ" and magnetoresistanceΔρ(H) measurements indicate the appearance of a spin glass state in La0.8Ca0.2MnO3. The nonlinear ac susceptibilityχ2,χ3 and magnetization curve M(H) show thatthe state in La0.8Ca0.2MnO3 is a reentrant spin glass state. We suggest that an SG state and a ferromagnetic state coexist at 108K＜T＜173K. There is a direct relationship between resistivityρ(T) and linear absorption part of ac suscepMeasurements of specific heat and Hall effect in La0.8 Ca0.2MnO3 for magnetic field between 0 and 8T and temperature between 0.3 and 300K are reported. The linear term of specific heat C(T) at low temperature shows the enhancement ofγarises mainly from electron phonon coupling. It is a characteristic of a Jahn-Teller material. The peak of specific heat appeared at 45K and the anomaly occurred at 1.97K may be due to crystal field effect. The transport properties may be interpreted by Fermi-liquid model.
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Wanjun, Jiang. "Magnetic and Transport Properties of Colossal Magnetoresistance Manganites and Magnetic Semiconductors." 2010. http://hdl.handle.net/1993/3987.
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Transition metal and related compounds have been extensively studied over the past several decades. These investigations revealed a wide range of behavior, encompassing colossal magnetoresistance (CMR), high-TC superconductivity, and magnetic semiconductivity, all of which continue to present fundamental challenges to the understanding of such phenomena.
There is, however, a close correlation between such characteristics and the appearance of magnetic order. This correlation underlies the present study, which focuses on the magnetic and transport behavior of various Manganese (Mn), Iron (Fe) and Cobalt (Co) containing materials, with particular emphasis on the nature of the magnetic order they display and the critical exponents that characterize the accompanying phase transition. The magnetic and transport properties of two specific systems will be covered: first various doped manganites from the series (La,Pr)1-x(Ca,Ba)xMnO3, and second the magnetic semiconductors Fe0.8Co0.2Si and Ga0.98Mn0.02As.
In the manganites, the influence of doping on; (i) the evolution of the metal-insulator transition (MIT) with composition; (ii) the universality class of the magnetic critical behavior associated with the paramagnetic to ferromagnetic transition, which occurs in the vicinity of a MIT with which CMR is associated; (iii) the mechanisms underlying ferromagnetism across the MIT; (iv) the correlation between the appearance of a Griffiths-like phase and CMR, and (v) the origin of Griffiths-like phase have been investigated. Four different systems have been studied: La1-xCaxMnO3 (0.18 ≤ x ≤ 0.27), La1-xBaxMnO3 (x ≤ 0.33), (La1-yPry)0.7Ca0.3Mn16/18O3 (y ≤ 0.85), and Pr1-xCaxMnO3 (x = 0.27, 0.29).
In Fe0.8Co0.2Si and Ga0.98Mn0.02As, the scaling between magnetization and conductivity has been the subject of ongoing debate. In bulk Fe0.8Co0.2Si, a novel scaling between the anomalous Hall effect (AHE) and the magnetization enables the anomalous Hall coefficient to be accurately determined. In turn, this enables the universality class for the transition to ferromagnetism to be established independently from the anomalous Hall conductivity. In an epitaxial (metallic) Ga0.98Mn0.02As microstructure, the magnetization has been indirectly determined from the AHE. Subsequent analysis yields magnetic critical exponents consistent with the Mean-Field model, direct support for which had previously been lacking.
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High, Grant Lysle. "Electrical transport properties and magnetism of Cr-Mo-Ru alloys." Thesis, 2014. http://hdl.handle.net/10210/11533.
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