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Author: Kazi Monirul Alam Alam Publisher: ISBN: Category : Magnetism Languages : en Pages : 107
Book Description
Electrons, the fundamental charge carriers in solid-state devices, possess three intrinsic properties: mass, charge and spin. Spin is a quantum mechanical property, but can be loosely visualized as a tiny "intrinsic" magnetic dipole moment attached to an electron. In conventional electron devices, spin magnetic moments point along random directions in space and play no significant role in device operation. In the emerging field of "spintronics" the central theme is to harness the spin degree of freedom of charge carriers to realize novel data storage and information processing technologies. Spintronic devices are already ubiquitous in state-of-the-art hard disks with large storage densities. A concerted global effort is underway to explore various spin-based information processing concepts, which can potentially be more energy-efficient than traditional charge-based electronics. In recent years, substantial research has been devoted to understanding carrier spin dynamics in metallic multilayers, tunnel junctions and inorganic semiconductors such as silicon, germanium and various III-V compounds. On the other hand, p-conjugated organic semiconductors that play a crucial role in organic electronics and displays are relatively new materials in the area of spintronics. Organic semiconductors offer several advantages (such as mechanical flexibility, chemical tunability of physical properties, low-cost and low-temperature processing) compared to their inorganic counterparts. The ability to control carrier spin dynamics in organic materials will open up possibility of new devices such as flexible non-volatile memories, spin-based organic light emitting diodes and spin filters. iii In this work, we have explored two key spin related phenomena in organic semiconductor nanostructures: (a) spin-polarized transport and (b) spin filtering. In the first sub-project, we explore spin transport in "nanowire" geometry instead of commonly studied thin film devices. Such experiments shed light on the spin relaxation mechanisms in organics and indicate ways to minimize such effects. Fabrication of organic nanowires with well-controlled geometry in the sub-100 nm range is a non-trivial task, and in this subproject we have developed a novel technique for this purpose. Spin transport in rubrene nanowires has been studied, which indicates significant suppression of spin relaxation in nanowire geometry compared to rubrene thin films. Our experimental data indicates that spin-orbit coupling is the dominant spin relaxation mechanism in rubrene nanowires. In the second sub-project, we explore spin filtering (transmission of one particular type of spin) through an organic nanostructure in which single wall carbon nanotubes (SWCNT) are wrapped with single stranded DNA (ssDNA) molecules. Efficient spin filtering has been observed in this system, which may enable magnetless spintronic devices in the future.
Author: Kazi Monirul Alam Alam Publisher: ISBN: Category : Magnetism Languages : en Pages : 107
Book Description
Electrons, the fundamental charge carriers in solid-state devices, possess three intrinsic properties: mass, charge and spin. Spin is a quantum mechanical property, but can be loosely visualized as a tiny "intrinsic" magnetic dipole moment attached to an electron. In conventional electron devices, spin magnetic moments point along random directions in space and play no significant role in device operation. In the emerging field of "spintronics" the central theme is to harness the spin degree of freedom of charge carriers to realize novel data storage and information processing technologies. Spintronic devices are already ubiquitous in state-of-the-art hard disks with large storage densities. A concerted global effort is underway to explore various spin-based information processing concepts, which can potentially be more energy-efficient than traditional charge-based electronics. In recent years, substantial research has been devoted to understanding carrier spin dynamics in metallic multilayers, tunnel junctions and inorganic semiconductors such as silicon, germanium and various III-V compounds. On the other hand, p-conjugated organic semiconductors that play a crucial role in organic electronics and displays are relatively new materials in the area of spintronics. Organic semiconductors offer several advantages (such as mechanical flexibility, chemical tunability of physical properties, low-cost and low-temperature processing) compared to their inorganic counterparts. The ability to control carrier spin dynamics in organic materials will open up possibility of new devices such as flexible non-volatile memories, spin-based organic light emitting diodes and spin filters. iii In this work, we have explored two key spin related phenomena in organic semiconductor nanostructures: (a) spin-polarized transport and (b) spin filtering. In the first sub-project, we explore spin transport in "nanowire" geometry instead of commonly studied thin film devices. Such experiments shed light on the spin relaxation mechanisms in organics and indicate ways to minimize such effects. Fabrication of organic nanowires with well-controlled geometry in the sub-100 nm range is a non-trivial task, and in this subproject we have developed a novel technique for this purpose. Spin transport in rubrene nanowires has been studied, which indicates significant suppression of spin relaxation in nanowire geometry compared to rubrene thin films. Our experimental data indicates that spin-orbit coupling is the dominant spin relaxation mechanism in rubrene nanowires. In the second sub-project, we explore spin filtering (transmission of one particular type of spin) through an organic nanostructure in which single wall carbon nanotubes (SWCNT) are wrapped with single stranded DNA (ssDNA) molecules. Efficient spin filtering has been observed in this system, which may enable magnetless spintronic devices in the future.
Author: Zeev Valy Vardeny Publisher: World Scientific ISBN: 9813230169 Category : Technology & Engineering Languages : en Pages : 1364
Book Description
This reference work on Spin in Organics contains four volumes dedicated to spin injection, spin transport, spin pumping, organic magnetic field effect, and molecular spintronics. The field of Organic Spintronics has accelerated and matured in the last dozen years with the realization of an organic spin-valve (in 2004) and magneto-resistance and magneto-electroluminescence in organic optoelectronic devices (2006).The book series is comprehensive in that it summarizes all aspects of Organic Spintronics to date. The first two volumes deal with spin injection, spin transport, spin manipulation and spin pumping into organic semiconductors. The main device that is thoroughly discussed here is the organic spin-valve, where spinterface states at the interface between the organic semiconductor and the ferromagnetic (FM) electrode has been the focus of many chapters. An interesting emerging subject is the role of chirality in the organic layer of the device. A relatively new method of achieving spin aligned carriers in organic semiconductors is spin pumping, where magnons in the FM substrate generate spin aligned carriers in the organic layer at the FM/organic interface.The third volume deals mainly with magnetic field effect in organic devices. Several spin-mixture processes that lead to magnetic field effect in devices and films are thoroughly discussed, such as hyperfine interaction, direct spin-orbit coupling, indirect spin-orbit coupling via Δg, triplet-triplet annihilation, and thermal spin alignment. The similarity between the magnetic field effect obtained in optoelectronic devices based on organic semiconductors and the novel hybrid organic-inorganic semiconductors is also a subject of intense interest. The fourth volume deals with spin in molecular films and devices. It includes thorough discussion of spin exchange interaction that leads to organic ferromagnets, as well as manifestation of various spin interactions in thin molecular films and devices.
Author: Evgeny Y. Tsymbal Publisher: CRC Press ISBN: 1439803781 Category : Science Languages : en Pages : 797
Book Description
In the past several decades, the research on spin transport and magnetism has led to remarkable scientific and technological breakthroughs, including Albert Fert and Peter Grunberg's Nobel Prize-winning discovery of giant magnetoresistance (GMR) in magnetic metallic multilayers. Handbook of Spin Transport and Magnetism provides a comprehensive, bal
Author: Karthik Raman Venkataraman Publisher: ISBN: Category : Languages : en Pages : 155
Book Description
The use of organic semiconductors to enable organic spintronic devices requires the understanding of transport and control of the spin state of the carriers. This thesis deals with the above issue, focusing on the interface between the organic semiconductor and the spin source. The morphology of the organic molecule at the interface is shown to play a dominant role in this study, influencing spin injection. The interface molecule morphology affects the form of interaction between the organic molecule and the ferromagnet. This interaction ranges from a weak Van der Waals' to a chemical interaction leading to charge transfer, hybridization and other interface chemistry. As a result, the spin-dependent density of states is modified, influencing the spin injection process. The first part of the thesis focuses on identifying the interface properties between the ferromagnet and the organic semiconductor, rubrene. This is performed in a vertical organic junction geometry using different interface characterization tools. The growth morphology of the rubrene molecule is shown to influence the electronic coupling between the molecule and the ferromagnet. This has a pronounced effect on the spin injection efficiency and the magnetoresistance signals in the devices. The complex nature of the top interface is dealt with in detail. These studies provide insights on the importance of tailoring the interface properties to control and realize optimum behavior. As an alternative to conventional ferromagnets, a spin-filter material, europium sulphide, is demonstrated as a spin-polarized source. Spin-filter materials have shown the possibility to inject spin-polarized electrons into the organic semiconductor at higher voltage bias. This knowledge encouraged to seek organic spin-filter materials. Understanding the importance of molecule morphology from the work on rubrene, the second part of the thesis involved the study on a new class of organic materials called the phenalenyl compounds. Study using the compound, Zinc methyl phenalenyl, was initiated that showed large magnetoresistance signals of 50% at 4.2 K to 20% at close to room temperature. The origin of this magnetoresistance is attributed to a new interface phenomena described by the spin-filtering effect. The interface molecule morphology is found to play a very important role at the interface inducing an antiferromagnetic state and dominating the device physics. This technique opens up a new approach to engineer the interface and realize new functional devices without worrying about the bulk disorder of the organic film. This thesis thus shows the feasibility of tuning the property of the interface using tailor-made molecules to realize new functional devices at room temperature that can lead to development of the field and technological applications.
Author: Brian Curtin O'Gorman Publisher: ISBN: Category : Languages : en Pages : 208
Book Description
Two of the principal phenomena observed and exploited in the field of spintronics are giant magnetoresistance (GMR) and spin transfer torque (STT). With GMR, the resistance of a magnetic multilayer is affected by the relative orientation of its magnetic layers due to (electron) spin dependent scattering. For the STT effect, a spin-polarized electric current is used to alter the magnetic state of a ferromagnet. Together, GMR and STT are at the foundation of numerous technologies, and they hold promise for many more applications. To achieve the high current densities (~1012 A/m2) that are necessary to observe STT effects, point contacts - constricted electrical pathways (~1-100 nm in diameter) between conducting materials - are often used because of their small cross-sectional areas. In this sense, we have explored STT in bilayer magnetic nanopillars, where an electric current was used to induce precession of a ferromagnetic layer. This precessional state was detected as an increase in resistance of the device, akin to GMR. Temperature dependent measurements of the onset of precession shed light on the activation mechanism, but raised further questions about its detailed theory. Point contacts can also be used as local sources or detectors of electrons. In this context, we have observed transverse electron focusing (TEF) in a single crystal of bismuth. TEF is a k-selective technique for studying electron scattering from within materials. Using lithographically fabricated point contacts, we have studied the temperature dependence of the relaxation time for ballistic electrons from 4.2 to 100 K. These measurements indicated a transition between electron-electron dominated scattering at low temperatures and electron-phonon scattering as the Debye temperature was approached. We present preliminary work toward a TEF experiment to measure spin dependent scattering from a non-magnet/magnet interface. We also investigated spin wave propagation in thin, magnetic waveguide structures. At the boundary between the waveguide and continuous magnetic film, spin wave rays were found to radiate into the film, or to reflect and form standing waves in the waveguide. A circular defect in the waveguide was observed to cause diffraction of spin waves, generating an interference pattern of higher modes of oscillation.
Author: Tianhan Liu Publisher: ISBN: Category : Physics Languages : en Pages : 0
Book Description
Semiconductor spintronics has been widely regarded as a viable pathway to overcome many limitations in the current microelectronics technology. Molecular spintronics, an emerging research area in spintronics, aims to incorporate the unique functionalities of organic components into the solid-state device architectures. The overarching theme of this dissertation research is to explore a new nonmagnetic pathway of spin injection and detection in semiconductor spintronics by employing chirality-induced spin selectivity (CISS) in chiral molecules.This dissertation begins with a study of spin transport in an inorganic semiconductor, the persistent photoconductor Si-doped Al0.3Ga0.7As. The persistent photoconductivity facilitates spin transport measurements on one and the same sample over a broad range of carrier densities across the insulator-metal transition (Chapter 3). Three-terminal (3T) and four-terminal (4T) Hanle measurements have been performed to ascertain the dependences of spin lifetimes on bias current and carrier density. The spin lifetimes in the AlGaAs channel are extracted from fittings to the Lorentzian function and one-dimensional spin drift-diffusion model. The comprehensive results from our experiments show broad similarities between 3T and 4T Hanle signals, providing evidence that 3T Hanle measurements in our systems do result from spin accumulation instead of spurious effects. The results provide a solid experimental basis for understanding the spin relaxation mechanisms in semiconductors. The second project (Chapter 4) focuses on the formation and micro/nano patterning of self-assembled monolayers (SAMs) of thiol molecules on the semiconductor GaAs. We demonstrated that by etching and passivating the GaAs surface with ammonium polysulfide, alkanethiol molecules can form high-quality SAMs by solution assembly. Moreover, using molecular patterning methods of dip-pen nanolithography and micro-contact printing, nanoscale and microscale thiol SAM patterns can be created directly on the prepared GaAs surface. The functionalities of the molecular SAMs were then demonstrated by using 4-aminothiophenol SAMs as templates for directed self-assembly of Au nanoparticles on GaAs. The experiments demonstrated the viability of the experimental techniques for fabricating molecular/semiconductor hybrid structures and bottom-up fabrication of nanoplasmonic structures. The unique combination of the physics knowledge and experimental skills from the first two projects laid the foundation for the implementation of my primary dissertation project: Utilization of CISS to generate spin polarization in semiconductors without using any magnetic materials. The two main methods of spin detection are the spin-valve effect and Hanle effect. For the spin-valve effect (Chapter 5), we fabricate vertical planar junctions of (Ga,Mn)As/[alpha]-helix L-polyalanine (AHPA-L) molecules/Au. The magnetoconductance (MC) of the junction is measured, which provided direct evidence for spin selective transport through chiral molecules assembled on a ferromagnetic semiconductor (Ga,Mn)As. Importantly, the junction structure in our experiments allowed for robust measurements of the bias dependences of MC, which show both a pronounced nonlinear-response component and a nontrivial linear-response component. Our results are in direct contradiction of the expectation of some theoretical models and provide an important constraint for a viable theory of CISS and its device manifestations. The Hanle effect, presented in Chapter 6, has been performed by the 3T configuration, in junctions of n-GaAs/AHPA-L molecules/Au, with the (Ga,Mn)As replaced by the non-magnetic Si-doped GaAs. The signals show two distinct components consistent with contributions from the Hanle effect and dynamic nuclear polarization respectively. The signals are observed to exhibit exceptional sensitivities to temperature, bias current, and the orientation of the applied magnetic field with respect to the junction plane. Details of the experimental results are not fully understood and warrant further experimental and theoretical investigation. The definitive demonstration of a CISS-induced Hanle effect in nonmagnetic semiconductors would be a significant step forward to a new paradigm in spintronics, namely, semiconductor spintronics free of any magnetic materials.
Author: Zeev Valy Vardeny Publisher: CRC Press ISBN: 1439806578 Category : Science Languages : en Pages : 354
Book Description
Major development efforts in organic materials research has grown for an array of applications. Organic spintronics, in particular, has flourished in the area of organic magneto-transport. Reflecting the main avenues of advancement in this arena, this volume explores spin injection and manipulation in organic spin valves, the magnetic field effect in organic light-emitting diodes (OLEDs), the spin transport effect in relation to spin manipulation, organic magnets as spin injection electrodes in organic spintronics devices, the coherent control of spins in organic devices using the technique of electronically detected magnetic resonance, and the possibility of using organic spin valves as sensors.
Author: Eugene Kamenetskii Publisher: Springer Nature ISBN: 3030628442 Category : Science Languages : en Pages : 587
Book Description
This book discusses theoretical and experimental advances in metamaterial structures, which are of fundamental importance to many applications in microwave and optical-wave physics and materials science. Metamaterial structures exhibit time-reversal and space-inversion symmetry breaking due to the effects of magnetism and chirality. The book addresses the characteristic properties of various symmetry breaking processes by studying field-matter interaction with use of conventional electromagnetic waves and novel types of engineered fields: twisted-photon fields, toroidal fields, and magnetoelectric fields. In a system with a combined effect of simultaneous breaking of space and time inversion symmetries, one observes the magnetochiral effect. Another similar phenomenon featuring space-time inversion symmetries is related to use of magnetoelectric materials. Cross-coupling of the electric and magnetic components in these material structures, leading to the appearance of new magnetic modes with an electric excitation channel – electromagnons and skyrmions – has resulted in a wealth of strong optical effects such as directional dichroism, magnetochiral dichroism, and rotatory power of the fields. This book contains multifaceted contributions from international leading experts and covers the essential aspects of symmetry-breaking effects, including theory, modeling and design, proven and potential applications in practical devices, fabrication, characterization and measurement. It is ideally suited as an introduction and basic reference work for researchers and graduate students entering this field.
Author: Kazi Monirul Alam Alam
Author: Kazi Monirul Alam Alam
Author: Zeev Valy Vardeny
Author: Evgeny Y. Tsymbal
Author: Fabio Taddei
Author: Karthik Raman Venkataraman
Author: Brian Curtin O'Gorman
Author: Patrik Recher
Author: Tianhan Liu
Author: Zeev Valy Vardeny
Author: Eugene Kamenetskii