Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
College of Natural and Computational Sciences >
Thesis - Physics >

Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2299

Advisors: Prof. P. Singh
Keywords: physics
Copyright: Jun-2010
Date Added: 3-May-2012
Publisher: AAU
Abstract: Conventional electronic devices rely on manipulating charge to produce desired func- tions, spintronic devices would manipulate both the charge flow and electron spin within that flow. This would add an extra degree of freedom to microelectronics and usher in the era of truly nanoelectronic devices. Research aimed at a whole new generation of electronic devices is underway by introducing electron spin as a new or additional physi- cal variable, and semiconductor devices that exploit this new freedom will operate faster and more efficiently than conventional microelectronic devices and offer new functionality that promises to revolutionize the electronics industry. In order to enable electronic devices in active part of operation efforts have been made to develop diluted magnetic semiconductors(DMS) in which small quantity of magnetic ion is introduced in to normal semiconductors. The first known such DMS are II-VI and III-V semiconductors diluted with magnetic ions like Mn, Fe, Co, Ni, etc. Most of these DMS exhibit very high electron and hole mobility and thus useful for high speed electronic devices. In this thesis we study a photo induced ferromagnetism and mechanism of ferromag- netism in diluted magnetic semiconductors by solving a Hamiltonian model that consists of localized magnetic moments interacting with photoexcited carriers. The mechanism for photo-induced ferromagnetism is coherence between conduction and valence bands induced by the light which leads to an optical exchange interaction. When light is inci- dent on the diluted magnetic semiconductors, electron and holes are created across the band gap. Photo excited carriers mediated a ferromagnetic interaction between the local- ized moments resulting in ferromagnetic state in the range of critical temperature. The ix situation is similar to the famous Rabi problem of a two state system coupled to time- dependent oscillating electric field. The time dependance of the light-matter interaction term is eliminated by a unitary transformation and the resulting Hamiltonian is solved by making a Bogoliubov-Valtain transformation. Since the system of electrons and holes in contact with the photon bath is considered in a steady state, we calculate the free energy of the system. Starting the free energy again we calculate the magnetization of the system in self-consistent mean field way. The magnetization and magnitude of Tc is determined by the photon energy incident on the system. By increasing the light coupling and frequency of the light, the transition temperature is increased.
URI: http://hdl.handle.net/123456789/2299
Appears in:Thesis - Physics

Files in This Item:

File Description SizeFormat
64754.14 kBAdobe PDFView/Open

Items in the AAUL Digital Library are protected by copyright, with all rights reserved, unless otherwise indicated.


  Last updated: May 2010. Copyright © Addis Ababa University Libraries - Feedback