No description available.

Thesis (Ph.D.)--Virginia Commonwealth University, 2008. / Prepared for: Dept. of Electrical Engineering. Title from thesis description page. Includes bibliographical references.

This thesis presents the result of the charge carrier injection and the subsequent transport from ferromagnetic material into organic semiconductor in the Alq3 based organic spin valves. In order to study the dominant charge carrier polarity in the Alq3 based spin valves, a number of single (Alq3) layer and double (Alq3 and N,N’-bis(3-methylphenyl)-N,N’- diphenylbenzidine (TPD)) layer organic semiconductor diode devices are constructed using both conventional electrode materials as well as ferromagnetic electrodes. Single layer devices are characterised by time of flight (ToF) and dark injection (DI) transient techniques with or without ferromagnetic anodes. Double layer devices are characterised using current-voltage-luminescence (j-V-L) measurements with or without ferromagnetic cathodes. Despite Alq3 being considered an electron transport material, we measure long range hole transport within the devices with matched electron and hole mobility at large electric fields. The substitution of a conventional Al cathode with a ferromagnet drastically suppresses electroluminescence in double layer devices, due to poor electron injection from the large work function ferromagnet. DI measurements using a ferromagnetic anode display characteristic charge trapping consistent with the presence of hybridized interface states (HINTS) between anode and organic semiconductor. The temperature dependent DI and ToF measurements demonstrate a reduced hole injection barrier in the presence of the HINTS in the ferromagnetic/organic interface that enables Alq3 based organic spin valves operate at small bias. We conclude that the dominant charge carriers in Alq3 based spin valves are holes, contrary to conventional wisdom, and that hole injection under small bias conditions is aided by HINTS.

No description available.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

No description available.

Thesis (M.S.)--State University of New York at Binghamton, Department of Physics, 2006. / Includes bibliographical references.

The impact of the spin degree of freedom on the transport properties of electrons traveling through magnetic materials has been known since the pioneer work of Mott [1]. Since then it has been demonstrated that the spin angular momentum plays a key role in the scattering process of electrons in magnetic multilayers. This role has been emphasized by the discovery of the Giant Magnetoresistance in 1988 by Fert and Grunberg [2, 3]. Among the numerous applications and effects that emerged in mesoscopic devices two mechanisms have attracted our attention during the course of this thesis: the spin transfer torque and the spin Hall effects. The former consists in the transfer of the spin angular momentum from itinerant carriers to local magnetic moments [4]. This mechanism results in the current-driven magnetization switching and excitations, which has potential application in terms of magnetic data storage and non-volatile memories. The latter, spin Hall effect, is considered as well to be one of the most fascinating mechanisms in condensed matter physics due to its ability of generating non-equilibrium spin currents without the need for any magnetic materials. In fact the spin Hall effect relies only on the presence of the spin-orbit interaction in order to create an imbalance between the majority and minority spins. The objective of this thesis is to investigate the impact of disorder on spin dependent transport phenomena. To do so, we identified three classes of systems on which such disorder may have a dramatic influence: (i) antiferromagnetic materials, (ii) impurity-driven spin-orbit coupled systems and (iii) two dimensional semiconducting electron gases with Rashba spin-orbit coupling. Antiferromagnetic materials - We showed that in antiferromagnetic spin-valves, spin transfer torque is highly sensitive to disorder, which prevents its experimental observation. To solve this issue, we proposed to use either a tunnel barrier as a spacer or a local spin torque using spin-orbit coupling. In both cases, we demonstrated that the torque is much more robust against impurities, which opens appealing venues for its experimental observation. Extrinsic spin-orbit coupled systems - In disordered metals accommodating spin orbit coupled impurities, it is well-known that spin Hall effect emerges due to spin dependent Mott scattering. Following a recent prediction, we showed that another effect coexists: the spin swapping effect, that converts an incoming spin current into another spin current by "swapping" the momentum and spin directions. We showed that this effect can generate peculiar spin torque in ultrathin magnetic bilayers. Semiconductors spintronics - This last field of research has attracted a massive amount of hope in the past fifteen years, due to the ability of coherently manipulating the spin degree of freedom through interfacial, so-called Rashba, spin-orbit coupling. However, numerical simulations failed reproducing experimental results due to coherent interferences between the very large number of modes present in the system. We showed that spin-independent disorder can actually wash out these interferences and promote the conservation of the spin signal. In the course of this PhD, we showed that while disorder-induced dephasing is usually detrimental to the transmission of spin information, in selected situation, it can actually promote spin transport mechanisms and participate to the enhancement of the desired spintronics phenomenon.

No description available.

Spintronics or electronics that utilizes the spin degree of freedom of a single charge carrier (or an ensemble of charge carriers) to store, process, sense or communicate data and information is a rapidly burgeoning field in electronics. In spintronic devices, information is encoded in the spin polarization of a single carrier (or multiple carriers) and the spin(s) of these carrier(s) are manipulated for device operation. This strategy could lead to devices with low power consumption. This dissertation investigates spin transport in one dimensional and two dimensional semiconductors, with a view to applications in spintronic devices.