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dc.contributor.advisorSatpathy, Sashi Sekhar, 1956-eng
dc.contributor.authorMishra, Subodhaeng
dc.date.issued2006eng
dc.date.submitted2006 Falleng
dc.descriptionThe entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.eng
dc.descriptionTitle from title screen of research.pdf file (viewed on August 6, 2007)eng
dc.descriptionVita.eng
dc.descriptionIncludes bibliographical references.eng
dc.descriptionThesis (Ph. D.) University of Missouri-Columbia 2006.eng
dc.descriptionDissertations, Academic -- University of Missouri--Columbia -- Physics.eng
dc.description.abstractThis thesis is a theoretical study of photo-induced ferro-magnetism in dilute magnetic semiconductors. When light is incident on these systems, electrons and holes are created across the band gap. These particles interact with the impurity magnetic moments and mediate ferro-magnetism when temperature is lowered. This is a situation similar to the famous Rabi problem of a two state system coupled to time-dependent oscillating electric field. Ours is a multi-state system with electrons and holes coupled to an oscillating electric field. This is a generalization of the Rabi problem which shows also a phase transition from para to ferromagnetic state. We first study some model one and two state systems. We show by performing appropriate unitary transformations, it is possible to eliminate the time from the time-dependent Hamiltonians and get the eigen energies. Since our system of electrons and holes in contact with the photon bath is in a steady state, we calculate the free energy of the system. We study the problem of phase transition in two different ways, one by constructing Bogoliubov-Valatin quasi particles and the other by BCS wave function approach as in the low-temperature superconducting phenomenon. This also establishes that BCS and BV approaches are equivalent mean-led methods. We calculate magnetization of the system in a self-consistent mean-field way. The magnetization and thereby the critical temperature is dependent on the photon energy incident on the system. By increasing the light coupling to the particles the transition temperature increases. Also by increasing the frequency of the light, the transition temperature is increased. Since more and more of the electrons and holes are created, these carriers mediate more with the magnetic moments and flip their moments into the ferro-magnetic state. It is also found that even when light energy is below the band-gap there is still magnetization and a ferro-magnetic state is still possible. It is interesting to find a linear dependence of critical temperature Tc on the coupling J².eng
dc.identifier.merlinb59275029eng
dc.identifier.oclc162665299eng
dc.identifier.urihttps://hdl.handle.net/10355/4413
dc.identifier.urihttps://doi.org/10.32469/10355/4413eng
dc.languageEnglisheng
dc.publisherUniversity of Missouri--Columbiaeng
dc.relation.ispartofcollectionUniversity of Missouri--Columbia. Graduate School. Theses and Dissertationseng
dc.subject.lcshFerromagnetismeng
dc.subject.lcshDiluted magnetic semiconductorseng
dc.titleTheory of photo-induced ferro-magnetism in dilute magnetic semiconductorseng
dc.typeThesiseng
thesis.degree.disciplinePhysics (MU)eng
thesis.degree.grantorUniversity of Missouri--Columbiaeng
thesis.degree.levelDoctoraleng
thesis.degree.namePh. D.eng


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