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1
Radovanovic, Pavle V. "Synthesis, spectroscopy, and magnetism of diluted magnetic semiconductor nanocrystals /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/8494.
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Kneip, Martin K. "Magnetization dynamics in diluted magnetic semiconductor heterostructures." kostenfrei, 2008. http://hdl.handle.net/2003/25822.
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Peleckis, Germanas. "Studies on diluted oxide magnetic semiconductors for spin electronic applications." Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20070821.145447/index.html.
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Norberg, Nicholas S. "Magnetic nanocrystals : synthesis and properties of diluted magnetic semiconductor quantum dots /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/8625.
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Ankiewicz, Amélia Olga Gonçalves. "Properties of self-assembled diluted magnetic semiconductor nanostructures." Doctoral thesis, Universidade de Aveiro, 2010. http://hdl.handle.net/10773/2681.
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Doutoramento em Engenharia FísicaEste trabalho centra-se na investigação da possibilidade de se conseguir um semicondutor magnético diluído (SMD) baseado em ZnO. Foi levado a cabo um estudo detalhado das propriedades magnéticas e estruturais de estruturas de ZnO, nomeadamente nanofios (NFs), nanocristais (NCs) e filmes finos, dopadas com metais de transição (MTs). Foram usadas várias técnicas experimentais para caracterizar estas estruturas, designadamente difracção de raios-X, microscopia electrónica de varrimento, ressonância magnética, SQUID, e medidas de transporte. Foram incorporados substitucionalmente nos sítios do Zn iões de Mn2+ e Co2+ em ambos os NFs e NCs de ZnO. Revelou-se para ambos os iões dopantes, que a incorporação é heterogénea, uma vez que parte do sinal de ressonância paramagnética electrónica (RPE) vem de iões de MTs em ambientes distorcidos ou enriquecidos com MTs. A partir das intensidades relativas dos espectros de RPE e de modificações da superfície, demonstra-se ainda que os NCs exibem uma estrutura core-shell. Os resultados, evidenciam que, com o aumento da concentração de MTs, a dimensão dos NCs diminui e aumentam as distorções da rede. Finalmente, no caso dos NCs dopados com Mn, obteve-se o resultado singular de que a espessura da shell é da ordem de 0.3 nm e de que existe uma acumulação de Mn na mesma. Com o objectivo de esclarecer o papel dos portadores de carga na medição das interacções ferromagnéticas, foram co-dopados filmes de ZnO com Mn e Al ou com Co e Al. Os filmes dopados com Mn, revelaram-se simplesmente paramagnéticos, com os iões de Mn substitucionais nos sítios do Zn. Por outro lado, os filmes dopados com Co exibem ferromagnetismo fraco não intrínseco, provavelmente devido a decomposição spinodal. Foram ainda efectuados estudos comparativos com filmes de ligas de Zn1-xFexO. Como era de esperar, detectaram-se segundas fases de espinela e de óxido de ferro nestas ligas; todas as amostras exibiam curvas de histerese a 300 K. Estes resultados suportam a hipótese de que as segundas fases são responsáveis pelo comportamento magnético observado em muitos sistemas baseados em ZnO. Não se observou nenhuma evidência de ferromagnetismo mediado por portadores de carga. As experiências mostram que a análise de RPE permite demonstrar directamente se e onde estão incorporados os iões de MTs e evidenciam a importância dos efeitos de superfície para dimensões menores que ~15 nm, para as quais se formam estruturas core-shell. As investigações realizadas no âmbito desta tese demonstram que nenhuma das amostras de ZnO estudadas exibiram propriedades de um SMD intrínseco e que, no futuro, são necessários estudos teóricos e experimentais detalhados das interacções de troca entre os iões de MTs e os átomos do ZnO para determinar a origem das propriedades magnéticas observadas.
This work focuses on the study of the possibility of achieving an intrinsic diluted magnetic semiconductor (DMS) based on ZnO. Detailed investigations of the structural and magnetic properties of transition metal (TM) doped ZnO structures, namely nanowires (NWs), nanocrystals (NCs), and thin films, were carried out. Various experimental techniques, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetic resonance, SQUID, and transport measurements were employed to structurally and magnetically characterize these samples. For both the ZnO NWs and NCs, Mn and Co ions were successfully incorporated as substitutional Mn2+ or Co2+, respectively, on Zn sites. For both types of doping, the TM incorporation was heterogeneous, since part of the electron paramagnetic resonance (EPR) spectrum stemmed from TM ions in distorted or TM enriched environments. Furthermore, in the case of the NCs, the relative intensities of the EPR spectra and surface modifications showed that the NCs exhibit a core-shell structure. Moreover, the results evidence decreasing NC size and increasing lattice distortions for increasing TM content. Finally, in the case of the Mn doped NCs, we were able to obtain the unique result that the shell thickness is very small, in the order of 0.3 nm, and that there is an accumulation of the Mn ions in the shell. To clarify the role of charge carriers in mediating ferromagnetic interactions, Mn, Al and Co, Al co-doped ZnO films were investigated. The Mn doped ZnO samples were clearly paramagnetic, the Mn ions being substitutional on Zn sites. On the other hand, the Co doped samples exhibited weak ferromagnetic order, which we believe to most probably arise from spinodal decomposition. Additionally, comparative investigations of Fe alloyed ZnO films were performed. As expected, second phases of spinel and iron oxide were found, and the samples exhibited ferromagnetic hysteresis loops at 300 K. These results support the indication that secondary phases are accountable for the magnetic behaviour detected in many ZnO systems. No evidence of carrier mediated ferromagnetism was observed. The experiments show that the EPR analysis allows us to directly demonstrate whether and where the TM ions are incorporated and evidence the importance of the surface effects at material dimensions below ~15 nm, for which coreshell structures are formed. The research carried out in the framework of this thesis demonstrates that for all studied samples, ZnO did not exhibit the behaviour of an intrinsic DMS, and in the future very detailed element specific investigations, both experimental and theoretical, of the exchange interactions of the transition metal ions with the ZnO host are necessary to assert the nature of the magnetic properties.
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Kneip, Martin [Verfasser]. "Magnetization Dynamics in Diluted Magnetic Semiconductor Heterostructures / Martin Kneip." München : GRIN Verlag, 2009. http://d-nb.info/1187730718/34.
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Dagnelund, Daniel. "Magneto-optical studies of dilute nitrides and II-VI diluted magnetic semiconductor quantum structures." Doctoral thesis, Linköpings universitet, Funktionella elektroniska material, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-54695.
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This thesis work aims at a better understanding of magneto-optical properties of dilute nitrides and II-VI diluted magnetic semiconductor quantum structures. The thesis is divided into two parts. The first part gives an introduction of the research fields, together with a brief summary of the scientific results included in the thesis. The second part consists of seven scientific articles that present the main findings of the thesis work. Below is a short summary of the thesis. Dilute nitrides have been of great scientific interest since their development in the early 1990s, because of their unusual fundamental physical properties as well as their potential for device applications. Incorporation of a small amount of N in conventional Ga(In)As or Ga(In)P semiconductors leads to dramatic modifications in both electronic and optical properties of the materials. This makes the dilute nitrides ideally suited for novel optoelectronic devices such as light emitting devices for fiber-optic communications, highly efficient visible light emitting devices, multi-junction solar cells, etc. In addition, diluted nitrides open a window for combining Si-based electronics with III-V compounds-based optoelectronics on Si wafers, promising for novel optoelectronic integrated circuits. Full exploration and optimization of this new material system in device applications requires a detailed understanding of their physical properties. Papers I and II report detailed studies of effects of post-growth rapid thermal annealing (RTA) and growth conditions (i.e. presence of N ions, N2 flow, growth temperature and In alloying) on the formation of grown-in defects in Ga(In)NP. High N2 flow and bombardment of impinging N ions on grown sample surface is found to facilitate formation of defects, such as Ga interstitial (Gai) related defects, revealed by optically detected magnetic resonance (ODMR). These defects act as competing carrier recombination centers, which efficiently decrease photoluminescence (PL) intensity. Incorporation of a small amount of In (e.g. 5.1%) in GaNP seems to play a minor role in the formation of the defects. In GaInNP with 45% of In, on the other hand, the defects were found to be abundant. Effect of RTA on the defects is found to depend on initial configurations of Gai related defects formed during the growth. In Paper III, the first identification of an interfacial defect at a heterojunction between two semiconductors (i.e. GaP/GaNP) is presented. The interface nature of the defect is clearly manifested by the observation of ODMR lines originating from only two out of four equivalent <111> orientations. Based on its resolved hyperfine interaction between an unpaired electronic spin (S=1/2) and a nuclear spin (I=1/2), the defect is concluded to involve a P atom at its core with a defect/impurity partner along a <111> direction. Defect formation is shown to be facilitated by N ion bombardment. In Paper IV, the effects of post-growth hydrogenation on the efficiency of the nonradiative (NR) recombination centers in GaNP are studied. Based on the ODMR results, incorporation of H is found to increase the efficiency of the NR recombination via defects such as Ga interstitials. In Paper V, we report on our results from a systematic study of layered structures containing an InGaNAs/GaAs quantum well, by the optically detected cyclotron resonance (ODCR) technique. By monitoring PL emissions from various layers, the predominant ODCR peak is shown to be related to electrons in GaAs/AlAs superlattices. This demonstrates the role of the SL as an escape route for the carriers confined within the InGaNAs/GaAs single quantum well. The last two papers are within a relatively new field of spintronics which utilizes not only the charge (as in conventional electronics) but also the quantum mechanical property of spin of the electron. Spintronics offers a pathway towards integration of information storage, processing and communications into a single technology. Spintronics also promises advantages over conventional charge-based electronics since spin can be manipulated on a much shorter time scale and at lower cost of energy. Success of semiconductor-based spintronics relies on our ability to inject spin polarized electrons or holes into semiconductors, spin transport with minimum loss and reliable spin detection. In Papers VI and VII, we study the efficiency and mechanism for carrier/exciton and spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe quantum well into nonmagnetic CdSe quantum dots (QD’s) by means of spin-polarized magneto PL combined with tunable laser spectroscopy. By means of a detailed rate equation analysis presented in Paper VI, the injected spin polarization is deduced to be about 32%, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process. In Paper VII, we present evidence that energy transfer is the dominant mechanism for carrier/exciton injection from the DMS to the QD’s. This is based on the fact that carrier/exciton injection efficiency is independent of the width of the ZnSe tunneling barrier inserted between the DMS and QD’s. In sharp contrast, spin injection efficiency is found to be largely suppressed in the structures with wide barriers, pointing towards increasing spin loss.
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GURUNG, TAK BAHADUR. "OPTICAL IMAGING OF EXCITON MAGNETIC POLARONS IN DILUTED MAGNETIC SEMICONDUCTOR QUANTUM DOTS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155658535.
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Enaya, Hani. "Nonvolatile Spin Memory based on Diluted Magnetic Semiconductor and Hybrid Semiconductor Ferromagnetic Nanostructures." NCSU, 2008. http://www.lib.ncsu.edu/theses/available/etd-05222008-214407/.
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The feasibility of nonvolatile spin-based memory device concepts is explored. The first memory device concept utilizes the electrically controlled paramagnetic-ferromagnetic transition in a diluted magnetic semiconductor layer (quantum well or dot) when the ferromagnetism in the diluted magnetic semiconductor is mediated by itinerant holes. The specific structure under consideration consists of a diluted magnetic semiconductor quantum well (or quantum dot) and a nonmagnetic quantum well, which acts as a hole reservoir, separated by a permeable barrier. The quantitative analysis is done by calculating the free energy of the system. Formation of two stable states at the same external conditions, i.e., bistability, is found feasible at temperatures below the Curie temperature with proper band engineering. The effects of scaling the magnetic quantum well to quantum dot on bistability are analyzed. The bit retention time, i.e., lifetime, with respect to spontaneous leaps between the two stable states is calculated. The write/erase and read operations are discussed as well as the dissipation energy. Also, potential logic operations are proposed. In the second memory concept, the active region is a semiconductor quantum dot sharing an interface with a dielectric magnetic layer. The operating principle of the device is based on the spontaneous magnetic symmetry breaking due to exchange interaction between the magnetic ions in the magnetic layer and the spins of the itinerant holes in the quantum dot. Room temperature operation is possible given the availability of insulating ferromagnetic or antiferromagnetic materials whose Curie temperature is above room temperature. The specific range of material parameters where bistability is achieved is found. Analysis is extended to different quantum dot and magnetic dielectric materials and designs. Influence of material choice and design on the memory robustness, i.e., lifetime, is discussed.
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Stirner, Thomas. "Theory of excitons and magnetic polarons in diluted magnetic semiconductor quantum well structures." Thesis, University of Hull, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262406.
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Huang, Lunmei. "Computational Material Design : Diluted Magnetic Semiconductors for Spintronics." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7800.
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Liu, Jingjing. "Diluted Magnetic Semiconductor Nanomaterials Fabrication by a Chemical Vapor Deposition Method." ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/426.
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Well-aligned DMS Zn1-xMnxO nanowires and nanorods were successfully synthesized in-situ using a chemical vapor deposition method. Low-dimensional nanostructures such as bowls and cages were deposited on a silicon surface downstream of the tube furnace. Variation of reaction temperature and Mn doping level were investigated on structure and properties of the as-grown nanomaterials. The as-grown nanowires and naorods are single crystalline wurtzite structure and possess a growth direction along the c axis. At 850 ºC, the most optimistic condition for ZnO crystal growth was obtained. At high reaction temperature 950ºC, Mn2+ were substitutionally doped into ZnO lattice, resulting in room-temperature ferromagnetic coupling with a saturated magnetization of 0.25emu/g. The ferromagnetic interaction is weakened, however, by larger concentration of Mn, due to the antiferromagnetic coupling of direct superexchange interaction between Mn2+. The well-aligned DMS 1-dimensional Mn doped ZnO nanostructures have great potential for application in spintronic nanodevices.
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Gupta, Shalini. "Growth of novel wide bandgap room temperature ferromagnetic semiconductor for spintronic applications." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33809.
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This work presents the development of a GaN-based dilute magnetic semiconductor (DMS) by metal organic chemical vapor deposition (MOCVD) that is ferromagnetic at room temperature (RT), electrically conductive, and possesses magnetic properties that can be tuned by n- and p-doping. The transition metal series (TM: Cr, Mn, and Fe) along with the rare earth (RE) element, Gd, was investigated in this work as the magnetic ion source for the DMS. Single- phase and strain-free GaTMN films were obtained. Optical measurements revealed that Mn is a deep acceptor in GaN, while Hall measurements showed that these GaTMN films were semi-insulating, making carrier mediated exchange unlikely. Hysteresis curves were obtained for all the GaTMN films, and by analyzing the effect of n- and p-dopants on the magnetic properties of these films it was determined that the magnetization is due to magnetic clusters. These findings are supported by the investigation of the effect of TM dopants in GaN nanostructures which reveal that TMs enhance nucleation resulting in superparamagnetic nanostructures. Additionally, this work presents the first report on the development of GaGdN by MOCVD providing an alternate route to developing a RT DMS. Room temperature magnetization results revealed that the magnetization strength increases with Gd concentration and can be enhanced by n- and p-doping, with holes being more efficient at stabilizing the ferromagnetic signal. The GaGdN films obtained in this work are single-phase, unstrained, and conductive making them suitable for the development of multifunctional devices that integrate electrical, optical, and magnetic properties.
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Leite, Douglas Marcel Gonçalves [UNESP]. "Propriedades estruturais, ópticas e magnéticas de filmes de GaMnN." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/100918.
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leite_dmg_dr_bauru.pdf: 3640633 bytes, checksum: adf6650360687a658c11b1cc1b69b693 (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
A recente busca por semicondutores magnéticos diluídos com propriedades magnéticas de interesse motivou este trabalho de crescimento de filmes de Ga1-xMnxN pelas técnicas de sputtering e epitaxia da fase de vapor de organometálicos (MOVPE). Os filmes são caracterizados estruturalmente por medidas de difração de raio X e microscopia eletrônica de transmissão, opticamente por transmitância óptica e espalhaçamento Raman, e magneticamente por medidas magnetização versus campo aplicado e versus temperatura. As principais diferenças entre os filmes de GaMnN preparados por sputerring e MOVPE referem-se à microestrutura e ao conteúdo de Mn: os primeiros são policristalinos e apresentam conteúdo de Mn até 9%, enquanto os últimos são monocristalinos com concentração de Mn até 1%. A alta concentraçao de Mn nos filmes crescidos por sputtering é possivelmente responsável pelo surgimento coletivo destes íons de Mn nas medidas magnéticas. Esse comportamento coletivo se identifica a partir de contribuição paramagnética de domínios isolados com alto vapor de momento magnético, o que se mostra consistente com a microestrutura apresentada por estes filmes. A alta concentração de Mn nos filmes preparados por sputtering também se mostra responsável por intensa absorção óptica abaixo da energia do gap, sendo esta relacionada a transições eletrônicas entre os estados localizados do Mn e as bandas de valência e condução do GaN. O contraste entre as propriedades dos filmes de GaMnN produzidos por sputtering e por MOVPE possibilita então um entendimento mais abrangente dos aspectos da incorporação de Mn no GaN e suas respectivas características estruturais, ópticas e magnéticas. Esse entendimento é importante para delinear a otimização deste material visando propriedades magnéticas de interesse
The current search for dilluted magnetic semiconductors with interesting magnetic properties has motivated the present work on growing GaMnN films by sputerring and metalorganic vapor phase epitaxy (MOVPE) techniques. The films are characterized by X-ray diffraction, transmission electron microscopy, optical transmission, Raman scattering, and by magnetization measurements. The main differece between the GaMnN grown by sputtering and those grown by MOVPE relates to their microstructure (polycrystalline/monocrystalline) and Mn content (up to 9%/1% respectively). The high Mn content in GaMnN samples grown by sputtering is probably responsible for a collective response on the magnetic measurements. This collective Mn response is identified as a high magnetic moment contribution which is consistent with sample microstructure. In the sputtered samples, the high Mn content is also responsible for strong subbandgap optical absorption related to eletronic transitions involving Mn states and the valence and conduction bands of GaN. The comparison between the properties of GaMnN films grown by different techniques is important in order to get a better understanding about the Mn incorporation in GaN. This understanding been important to define the next steps regarding the optimization of this material
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Liu, William K. "Electron spin dynamics in quantum dots, and the roles of charge transfer excited states in diluted magnetic semiconductors /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8588.
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Leite, Douglas Marcel Gonçalves. "Propriedades estruturais, ópticas e magnéticas de filmes de GaMnN /." Bauru : [s.n.], 2011. http://hdl.handle.net/11449/100918.
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Orientador: José Humberto Dias da SilvaBanca: Jair Scarminio
Banca: Alexys Bruno Alfonso
Banca: Pascoal José Giglio Pagliuso
Banca: Luis Vicente de Andrade Scalvi
O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp
Resumo: A recente busca por semicondutores magnéticos diluídos com propriedades magnéticas de interesse motivou este trabalho de crescimento de filmes de Ga1-xMnxN pelas técnicas de sputtering e epitaxia da fase de vapor de organometálicos (MOVPE). Os filmes são caracterizados estruturalmente por medidas de difração de raio X e microscopia eletrônica de transmissão, opticamente por transmitância óptica e espalhaçamento Raman, e magneticamente por medidas magnetização versus campo aplicado e versus temperatura. As principais diferenças entre os filmes de GaMnN preparados por sputerring e MOVPE referem-se à microestrutura e ao conteúdo de Mn: os primeiros são policristalinos e apresentam conteúdo de Mn até 9%, enquanto os últimos são monocristalinos com concentração de Mn até 1%. A alta concentraçao de Mn nos filmes crescidos por sputtering é possivelmente responsável pelo surgimento coletivo destes íons de Mn nas medidas magnéticas. Esse comportamento coletivo se identifica a partir de contribuição paramagnética de domínios isolados com alto vapor de momento magnético, o que se mostra consistente com a microestrutura apresentada por estes filmes. A alta concentração de Mn nos filmes preparados por sputtering também se mostra responsável por intensa absorção óptica abaixo da energia do gap, sendo esta relacionada a transições eletrônicas entre os estados localizados do Mn e as bandas de valência e condução do GaN. O contraste entre as propriedades dos filmes de GaMnN produzidos por sputtering e por MOVPE possibilita então um entendimento mais abrangente dos aspectos da incorporação de Mn no GaN e suas respectivas características estruturais, ópticas e magnéticas. Esse entendimento é importante para delinear a otimização deste material visando propriedades magnéticas de interesse
Abstract: The current search for dilluted magnetic semiconductors with interesting magnetic properties has motivated the present work on growing GaMnN films by sputerring and metalorganic vapor phase epitaxy (MOVPE) techniques. The films are characterized by X-ray diffraction, transmission electron microscopy, optical transmission, Raman scattering, and by magnetization measurements. The main differece between the GaMnN grown by sputtering and those grown by MOVPE relates to their microstructure (polycrystalline/monocrystalline) and Mn content (up to 9%/1% respectively). The high Mn content in GaMnN samples grown by sputtering is probably responsible for a collective response on the magnetic measurements. This collective Mn response is identified as a high magnetic moment contribution which is consistent with sample microstructure. In the sputtered samples, the high Mn content is also responsible for strong subbandgap optical absorption related to eletronic transitions involving Mn states and the valence and conduction bands of GaN. The comparison between the properties of GaMnN films grown by different techniques is important in order to get a better understanding about the Mn incorporation in GaN. This understanding been important to define the next steps regarding the optimization of this material
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Leite, Douglas Marcel Gonçalves. "Efeitos estruturais e ópticos da incorporação de Mn em filmes nanocristalinos de 'GA IND.1-x'MN IND.XN' preparados por sputtering reativo /." Bauru : [s.l.], 2007. http://hdl.handle.net/11449/88488.
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Orientador: José Humberto Dias da SilvaBanca: Carlos Frederico de Oliveira Graeff
Banca: Antonio Ricardo Zanatta
O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp
Resumo: A recente descoberta de propriedades ferromagnéticas em alguns semicondutores magnéticos diluídos (DMS) trouxe a esta classe de materiais um grande potencial para aplicações em dispositivos de controle de spin. Um DMS é basicamente formado por um semicondutor dopado por íons magnéticos, os quais têm o papel de criar um momento magnético local e também, em algumas situações, de introduzir portadores livres no material. Entre os DMSs conhecidos, o 'GA IND.1-x'MN IND.XN' surge como o mais forte candidato a aplicações práticas por apresentar até o momento a mais alta temperatura de transição ferromagnética ('T IND.C' 'DA ORDEM DE' 400 k). Até o presente, os filmes de 'GA IND.1-x'MN IND.XN' com propriedades ferromagnéticas relatados na literatura foram preparados por epitaxia por feixe molecular (MBE). Neste trabalho, descrevemos a preparação de filmes nanocristalinos de 'GA IND.1-x'MN IND.XN' com diferentes conteúdos de Mn (0,00 'MENOR' x 'MENOR' 0,18) pela técnica de RF-magnetron sputtering reativo. Analisamos os efeitos da incorporação de Mn na estrutura e nas propriedades ópticas destes filmes através de medidas de difração de raios-X e de absorção óptica entre o ultravioleta (6,5 eV) e infravermelho próximo (1,4 eV). Os resultados apontam um aumento do parâmetro de rede e do índice de refração, uma diminuição do gap ótico e um aumento da densidade de estados de defeitos no interior do gap conforme se aumenta o conteúdo de Mn nos filmes de 'GA IND.1-x'MN IND.XN' preparados por sputtering. Estes resultados são semelhantes aos reportados para a incorporação de Mn em filmes monocristalinos de 'GA IND.1-x'MN IND.XN' com propriedades ferromagnéticas preparados por MBE.
Abstract: The recent discoveries related to the ferromagnetic properties in some diluted magnetic semiconductors (DMS) have attracted considerable attention on this class of material due to their potential application on spin control devices. A DMS is basically formed by a semiconductor doped with magnetic ions with the purpose of creating local magnetic moments and, in some situations, to introduce free carriers in the material. Among the known DMSs, 'GA IND.1-x'MN IND.XN' is the one with the highest ferromagnetic transition temperature ('T IND.C' 'DA ORDEM DE' 400 k), and it is consequently on of the stronger candidates for practical applications. Until now, the 'GA IND.1-x'MN IND.XN' films with ferromagnetic properties described in the literature were prepared by molecular beam epitaxy (MBE). In this work, we report the preparation of nanocrystalline 'GA IND.1-x'MN IND.XN' films (0,00 'MENOR' x 'MENOR' 0,18) by reactive RF-magnetron sputtering technique. We analyzed the Mn incorporation effects on structure and optical properties of the films by X-ray diffraction measurements and optical absorption between UV (6,5 eV) and near infrared (1,4 eV). The results show the increase of the lattice parameters and of the refractive index, a decrease of the optical gap and a increase of defect states in the gap when Mn concentration is increased. These results are similar to those reported for Mn incorporation in monocrystalline 'GA IND.1-x'MN IND.XN' films prepared by MBE with ferromagnetic properties.
Mestre
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Laura, M. Robinson. "USING TIME-RESOLVED PHOTOLUMINESCENCE SPECTROSCOPY TO EXAMINE EXCITON DYNAMICS IN II-VI SEMICONDUCTOR NANOSTRUCTURES." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin980259259.
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Leite, Douglas Marcel Gonçalves [UNESP]. "Efeitos estruturais e ópticos da incorporação de Mn em filmes nanocristalinos de 'GA IND.1-x'MN IND.XN' preparados por sputtering reativo." Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/88488.
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leite_dmg_me_bauru.pdf: 1278982 bytes, checksum: f2b696ae90b2738246ee3c7750b37751 (MD5)A recente descoberta de propriedades ferromagnéticas em alguns semicondutores magnéticos diluídos (DMS) trouxe a esta classe de materiais um grande potencial para aplicações em dispositivos de controle de spin. Um DMS é basicamente formado por um semicondutor dopado por íons magnéticos, os quais têm o papel de criar um momento magnético local e também, em algumas situações, de introduzir portadores livres no material. Entre os DMSs conhecidos, o 'GA IND.1-x'MN IND.XN' surge como o mais forte candidato a aplicações práticas por apresentar até o momento a mais alta temperatura de transição ferromagnética ('T IND.C' 'DA ORDEM DE' 400 k). Até o presente, os filmes de 'GA IND.1-x'MN IND.XN' com propriedades ferromagnéticas relatados na literatura foram preparados por epitaxia por feixe molecular (MBE). Neste trabalho, descrevemos a preparação de filmes nanocristalinos de 'GA IND.1-x'MN IND.XN' com diferentes conteúdos de Mn (0,00 'MENOR' x 'MENOR' 0,18) pela técnica de RF-magnetron sputtering reativo. Analisamos os efeitos da incorporação de Mn na estrutura e nas propriedades ópticas destes filmes através de medidas de difração de raios-X e de absorção óptica entre o ultravioleta (6,5 eV) e infravermelho próximo (1,4 eV). Os resultados apontam um aumento do parâmetro de rede e do índice de refração, uma diminuição do gap ótico e um aumento da densidade de estados de defeitos no interior do gap conforme se aumenta o conteúdo de Mn nos filmes de 'GA IND.1-x'MN IND.XN' preparados por sputtering. Estes resultados são semelhantes aos reportados para a incorporação de Mn em filmes monocristalinos de 'GA IND.1-x'MN IND.XN' com propriedades ferromagnéticas preparados por MBE.
The recent discoveries related to the ferromagnetic properties in some diluted magnetic semiconductors (DMS) have attracted considerable attention on this class of material due to their potential application on spin control devices. A DMS is basically formed by a semiconductor doped with magnetic ions with the purpose of creating local magnetic moments and, in some situations, to introduce free carriers in the material. Among the known DMSs, 'GA IND.1-x'MN IND.XN' is the one with the highest ferromagnetic transition temperature ('T IND.C' 'DA ORDEM DE' 400 k), and it is consequently on of the stronger candidates for practical applications. Until now, the 'GA IND.1-x'MN IND.XN' films with ferromagnetic properties described in the literature were prepared by molecular beam epitaxy (MBE). In this work, we report the preparation of nanocrystalline 'GA IND.1-x'MN IND.XN' films (0,00 'MENOR' x 'MENOR' 0,18) by reactive RF-magnetron sputtering technique. We analyzed the Mn incorporation effects on structure and optical properties of the films by X-ray diffraction measurements and optical absorption between UV (6,5 eV) and near infrared (1,4 eV). The results show the increase of the lattice parameters and of the refractive index, a decrease of the optical gap and a increase of defect states in the gap when Mn concentration is increased. These results are similar to those reported for Mn incorporation in monocrystalline 'GA IND.1-x'MN IND.XN' films prepared by MBE with ferromagnetic properties.
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Cao, Chong Long. "Modélisation de la dynamique de spin d'un atome magnétique individuel dans une boîte quantique." Thesis, Grenoble, 2012. http://www.theses.fr/2011GRENY062/document.
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Nous avons étudié la dynamique de spin d'un atome de Mn inséré dans une boite quantique CdTe. Nos résultats montrent que la relaxation de spin du Mn est plus rapide lorsque la boite quantique contient un exciton. Ceci peut permettre une orientation optique du spin du Mn. Le mélange de bande de valence est le paramètre essentiel permettant la relaxation rapide du spin du Mn dans le champ d'échange de l'exciton. Ce mélange de bande de valence est controlé par la forme et les contraintes dans la boite quantique. L'influence de ces paramètres sur la dynamique du pompage optique a été analysée en détail. Nos simulations du pompage optique sont en bon accord avec les expériences. La dynamique cohérente d'un Mn individuel a aussi été étudiée. L'influence sur le pompage optique de la dynamique cohérente du spin électronique et nucléaire est discutée. Nous avons montré que le couplage entre spin électronique et nucléaire peut être contrôlé optiquement permettant une manipulation du spin du Mn. Nous avons finalement montré que la combinaison d'une excitation résonante optique et micro-onde peut être utilisée pour détecter optiquement la résonance magnétique d'un Mn dans une boite quantique CdTeWe have studied the spin dynamics of an individual Mn atom embedded a CdTe quantum dot. Our results show that the Mn spin relaxation is faster when the quantum dot contains an exciton. This can result in an optical orientation of the Mn spin. The valence band mixing is the critical parameter for the fast relaxation rates of the Mn spin in the exchange field of the exciton. This valence band mixing is controlled by the shape and strain of the quantum dot. The influence of these parameters on the optical pumping dynamics were analyzed in detail. Our simulation of optical pumping are in good agreement with experiments. The coherent dynamics of an individual Mn spin was also investigated. We discussed the influence of the coherent dynamics of the coupled electronic and nuclear spins on the optical pumping. We have shown that optically controlled coupling between electronic and nuclear spins could be used for Mn spin switching. We finally demonstrated that the combination of resonant laser and microwave fields can be used to optically detect the magnetic resonance of a Mn spin in a CdTe quantum dot
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Frey, Alexander [Verfasser], and Karl [Akademischer Betreuer] Brunner. "Spin-Dependent Tunneling and Heterovalent Heterointerface Effects in Diluted Magnetic II-VI Semiconductor Heterostructures / Alexander Frey. Betreuer: Karl Brunner." Würzburg : Universitätsbibliothek der Universität Würzburg, 2013. http://d-nb.info/1037311388/34.
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Jeong, Byoung-Seong. "Growth and ferromagnetic semiconducting properties of titanium dioxide thin films an oxide-diluted magnetic semiconductor (o-dms) for spintronics /." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0004240.
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Nayak, Sanjeev Kumar Verfasser], Peter [Akademischer Betreuer] Entel, and Wolfram [Akademischer Betreuer] [Hergert. "A treatise on first-principles studies of ZnO as diluted magnetic semiconductor / Sanjeev Kumar Nayak. Gutachter: Wolfram Hergert. Betreuer: Peter Entel." Duisburg, 2012. http://d-nb.info/1022791036/34.
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Nayak, Sanjeev Kumar [Verfasser], Peter Akademischer Betreuer] Entel, and Wolfram [Akademischer Betreuer] [Hergert. "A treatise on first-principles studies of ZnO as diluted magnetic semiconductor / Sanjeev Kumar Nayak. Gutachter: Wolfram Hergert. Betreuer: Peter Entel." Duisburg, 2012. http://nbn-resolving.de/urn:nbn:de:hbz:464-20120516-134709-2.
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Knapp, Alexander Gerhard [Verfasser], and J. [Gutachter] Geurts. "Resonant Spin Flip Raman-Spectroscopy of Electrons and Manganese-Ions in the n-doped Diluted Magnetic Semiconductor (Zn,Mn)Se:Cl / Alexander Gerhard Knapp ; Gutachter: J. Geurts." Würzburg : Universität Würzburg, 2019. http://d-nb.info/1193927218/34.
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Alho, Bruno de Pinho. "Estudo de nano estruturas diluídas magnéticas na presença de campos externos aplicados." Universidade do Estado do Rio de Janeiro, 2008. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=703.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorNeste trabalho abordamos algumas propriedades físicas associadas ao transporte spintrônico de nanoestruturas formadas por camadas de semicondutor diluído magnético (SDM) e semicondutor convencional submetidas a campos elétrico e magnético cruzados. O campo elétrico é aplicado na direção de crescimento da nanoestrutura e o campo magnético é aplicado perpendicularmente a essa direção. Estuda mos duas configurações de nanoestruturas onde o SDM localiza-se no poço quântico ou nas barreiras. Mostramos que é possível encontrar um potencial efetivo tipo poço de potencial duplo para um intervalo de intensidades de campos externos, altura da barreira de potencial e largura de poço quântico parabólico. Em tal condição esse sistema pode ser visto como um dispositivo spintrônico chamado filtro de spin, pois consegue selecionar polarizações de spin em diferentes regiões da nanoestrutura.
In the present work we studied properties of the spintronic transport of nanostructures formed by layers of diluted magnetic semiconductors (DMS) and conventional semiconductors with crossed fields applied. The electric field is in the growth direction and the magnetic field is perpendicular t o this one. We studied two configurations of nanostructures where the DMS is located in the barriers or in the well. We will show the possibility of the formation of a double quantum well like effective potential for different values of the applied fields intensities, barriers height and quantum well width. In this situation the system can be seen as a spintronic device called spin filter, since it can control the spin polarization in different regions of the nanostructure.
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Mishra, Subodha. "Theory of photo-induced ferro-magnetism in dilute magnetic semiconductors." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4413.
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Thesis (Ph. D.) University of Missouri-Columbia, 2006.The 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. Title from title screen of research.pdf file (viewed on August 6, 2007) Includes bibliographical references.
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Tanaka, Hiroki. "Zeeman Splitting Caused by Localized sp-d Exchange Interaction in Ferromagnetic GaMnAs Observed by Magneto-Optical Characterization." Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1441982108.
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Barate, Philippe. "Génération et détection optique d'ondes de spin dans les puits quantiques CdMnTe dopés n." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2010. http://tel.archives-ouvertes.fr/tel-00587167.
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Durant cette thèse, on utilise des impulsions lasers pour générer et détecter des excitations dans des puits CdMnTe dopés n dont la concentration en Mn est très faible. La technique employé est une technique pompe-sonde qui permet de suivre temporellement les excitations générées. On identifiera les ondes de spin de vecteur d'onde nul et on essaiera de les caractériser. On verra que l'on excite et que l'on observe un mode d'excitation inattendu lié aux spins des électrons du manganèses. On développera un modèle qui permettra d'expliquer ce nouveau mode et d'avoir accès à une caractéristique du gaz 2D d'électrons : ça polarisation. Cette caractéristique est fortement liée aux interactions coulombiennes dans le gaz, et nos mesures sont comparées aux dernières théories sur le sujet. Nos mesures et notre théorie sont compatibles avec ces théories et d'autre mesures effectués par d'autres techniques.
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Wang, Weigang. "Spin-dependent transport in magnetic tunnel junctions and diluted magnetic semiconductors." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 184 p, 2009. http://proquest.umi.com/pqdweb?did=1654494821&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Giddings, Alexander Devin. "Dilute magnetic semiconductor nanostructures." Thesis, University of Nottingham, 2008. http://eprints.nottingham.ac.uk/10521/.
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The prospect of a new generation of electronic devices based on the fundamental quantum property of angular momentum, known as spin, has led to the rapidly developing field of spintronics. It is envisioned that these advanced devices will have significant advantages over traditional charge based electronics in properties such as speed, power consumption and long coherence times. By combining the properties of magnetics with that of semiconductors, the novel class of materials known as dilute magnetic semiconductors (DMSs) are considered a promising system for exhibiting spintronic functionality. These materials are created by using molecular beam epitaxy (MBE) to incorporate into traditional semiconductors a quantity of transition metal atoms sufficient that ferromagnetism is exhibited. The most widely studied DMS is (Ga,Mn)As which has well characterised behaviour and can be processed using standard III-V fabrication techniques, thus providing an excellent basis for further study. In this research the properties of (Ga,Mn)As based systems are studied as the material dimensions are reduced to nanometre length scales. Three complementary approaches are used for this purpose. The first is to use ultra-high-resolution electron-beam lithography to construct devices. By being able to selectively remove material, laterally patterned structures can have sizes as small as 10 nm. The second approach is to exploit the atomic layer growth of MBE to allow the construction of epilayers and heterostructures with well defined vertical compositions. Thirdly, a theoretical k.p kinetic-exchange model allows the simulation of multilayer structures and an exploration of the parameter spaces available in such materials. Two systems are considered: lateral nanoconstricted magnetic tunnel junctions and vertically defined magnetic superlattices. The nanoconstrictions are analysed using low temperature magnetotransport techniques and novel anisotropic magnetoresistance (MR) effects are measured. Primarily, tunnelling anisotropic magnetoresistance (TAMR) is observed, demonstrating that it is a generic property of ferromagnetic tunnel devices and is therefore of wide interest for other spintronic systems. Secondarily, anisotropic switching behaviour is observed and is interpreted as Coulomb blockade anisotropic magnetoresistance (CBAMR). Additionally, the significance of the processing stages and material properties are highlighted. The magnetic superlattices are firstly considered on a theoretical basis in order to determine structural parameters in which a new MR effect might be observed. This effect derives from the interlayer exchange coupling (IEC) between the magnetic layers which can either be in parallel or opposed orientations. Based on the calculations, samples are measured using low temperature magnetotransport and magnetometry techniques in order to explore the possibility of some of the dramatic properties predicted in magnetic superlattice structures.
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Liu, Mingde. "Magnetization-steps spectroscopy in dilute magnetic semiconductors and in molecular magnetism /." Thesis, Connect to Dissertations & Theses @ Tufts University, 1998.
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Thesis (Ph.D.)--Tufts University, 1998 .Adviser: Yaacov Shapira. Submitted to the Dept. of Physics. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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Le, Gall Claire. "Dynamique et contrôle optique d'un spin individuel dans une boîte quantique." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00670963.
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Nous avons étudié les propriétés dynamique d'un spin individuel dans une boite quantique de semiconducteur II-VI (spin d'un atome de Mn ou electron résident). Une boîte quantique comportant un atome de manganese présente six raies qui permettent de sonder optiquement l'état de spin du Manganese. Des expériences pompe-sonde réalisées sur boîte unique ont permit de montrer que le spin du Mn peut être orienté optiquement en quelques dizaines de ns, que le temps de vie $T_1$ de ce spin est supérieur à la $mu$s, et que le pompage optique en champ nul est controlé par une anisotropie magnétique induite par les contraintes. Par ailleurs, dans le but d'identifier les mechanismes du pompage optique, nous avons mis en évidence des processus de relaxation de spin au sein du système exciton-manganese, durant la durée de vie de ce dernier. Enfin, nous avons mis en evidence un effet Stark optique sur chacune des raies d'une boîte quantique magnétique. Concernant la dynamique d'un électron dans une boîte quantique II-VI, nous avons mis en évidence le pompage du spin de l'électron résident ainsi que des noyaux.
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Onofre, Ramirez Yina Julieth. "Síntese e caracterização de filmes do sistema Zn(1−x)CoxO obtidos por spray pirólise." Universidade Federal de São Carlos, 2016. https://repositorio.ufscar.br/handle/ufscar/8774.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
We report a systematic study on the structural, morphological and optical properties of Zn1−xCoxO thin films grown by spray pyrolysis. The employed nominal concentrations were up to 15 Co %. The films were deposited on glass substrates between 220-300 o C using precursors such as zinc acetate and cobalt acetate in aqueous solutions. The effects of Co-doping on structural, morphological and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical transmittance and absorbance as well as photoluminescence (PL). The XRD results indicated that all films are polycrystalline with wurtzite crystal structure, a preferential growth direction in c-axis, and no secondary phases. SEM images generally showed uniform surface, and few regions have irregularities due to effects of the inclusion of cobalt as well as substrate deposition temperature. The spectra of transmittance and absorbance exhibited the transitions d-d due to Co2+ ion, a redshift of the absorption-edge and changes in the absorption band intensity with increasing of nominal Co-doping. These observations revealed the substitution of Zn ions Zn2+ and the presence of Co in the state 2+ in tetrahedral coordination in the ZnO lattice. Furthermore, there was a narrowing in band gap of 28 meV by percentage of Co inserted into the lattice. The PL spectra of ZnCoO samples presented three bands associated to near-band-edge absorption (NBE), structural defects and intratomic emissions of Co2+. Their optical emissions were characterized by the presence of traps which capture carriers and affect significantly the emissions. Through a qualitative model in a temperature range we interpreted these traps as potential fluctuations up to 17 meV. We also discussed the annealing in selected samples.
Apresentamos um estudo sistemático sobre as propriedades estruturais, morfológicas e ópticas de filmes Zn1−xCoxO com concentrações nominais de Co até 15% obtidos por spray pirólise. Os filmes foram depositados sobre substratos de vidro entre 220 - 300 oC, utilizando como precursores acetato de zinco e acetato de cobalto em solução aquosa. Os efeitos da dopagem com Co nas propriedades estruturais, morfológicas e ópticas foram estudados por difração de raios-X (DRX), microscopia eletrônica de varredura (MEV), transmitância e absorbância óptica, e fotoluminescência (PL). Os resultados de DRX indicaram que todos os filmes são policristalinos, com estrutura cristalina do tipo wurtzita e direção de crescimento preferencial no eixo c, com ausência de fases secundárias. As imagens do MEV, em geral, mostraram que as superfícies são uniformes, com irregularidades em algumas regiões devido aos efeitos da inserção de Cobalto e da temperatura de deposição do substrato. Nos espectros de transmitância e absorbância, observaram-se a presença das transições d-d do íon de Co2+, o deslocamento da borda de absorção para baixas energias, e a variação da intensidade da banda de absorção das transições d-d com o aumento da dopagem nominal de Co. Estas observações revelaram a substituição dos íons de Zn2+ e a presença de Co no estado +2 na coordenação tetraédrica na rede do ZnO. Além disso, houve uma redução da energia do bandgap de 28 meV por porcentagem de Co inserido na rede. Os espectros de PL das amostras de ZnO dopado com Co apresentaram três bandas associadas à emissão próxima à borda de absorção óptica, defeitos estruturais e emissão intratômica do Co2+. A emissão óptica dos filmes foi caracterizada pela presença de armadilhas que localizam os portadores de carga e afetam significativamente as bandas de emissão no intervalo de temperatura estudado. Através de um modelo qualitativo interpretamos estas armadilhas como flutuações de potencial com profundidades de até 17 meV. Discutimos também o tratamento térmico em amostras selecionadas.
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Gatuna, Ngigi wa. "Intrinsic vacancy chalcogenides as dilute magnetic semiconductors : theoretical investigation of transition-metal doped gallium selenide /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10595.
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Tran, Lien. "InSb semiconductors and (In,Mn)Sb diluted magnetic semiconductors." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16334.
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Im Rahmen dieser Arbeit wurden InSb- und verdünnt-magnetische In_{1-x}Mn_xSb Filme mittels Gasquellen-Molekularstrahlepitaxie hergestellt und deren strukturelle und elektronische Eigenschaften untersucht. Die 2 μm InSb-Dünnschichten wurden sowohl auf GaAs(001)-Substrat als auch um 4° in Richtung [110] fehlgeschnittenem Si(001)-Substrat hergestellt. Optimierte InSb-Schichten direkt auf GaAs zeigen eine hohe kristalline Qualität, niedriges Rauschen und eine Elektronenbeweglichkeit von 41100 cm^2/Vs bei 300 K. Die Ladungsträgerkonzentration beträgt etwa 2,9e16 cm^{-3}. Um InSb-Dünnschichten guter Qualität auf Si-Substrat zu realisieren, wurden fehlgeschnittene Substrate benutzt. Zur Reduzierung der Gitterfehlanpassung wurden Pufferschichten gewachsen. Eine Elektronenmobilität von 24000 cm^2/Vs und Ladungsträgerkonzentration von 2,6e16 cm^{-3} wurden bei 300 K nachgewiesen. Diese Probe enthält ein 0,06 μm GaAs/AlSb-Supergitter als Pufferschicht (Wachstumstemperatur war 340°C). Diese Probe zeigt der höheren Dichte der Microtwins und Stapelfehler als auch den Threading-Versetzungen in der schnittstellennahen Region geschuldet. Die Deep-Level Rauschspektren zeigen die Existenz von Deep-Levels sowohl in GaAs- als auch in Si-basierten Proben. Die InSb-Filme auf Si-Substrat zeigen einen kleineren Hooge-Faktor im Vergleich zu Schichten auf GaAs (300 K). Unter Anwendung der optimierten Wachstumsbedingungen für InSb/GaAs wurden verdünnt-magnetische In_{1-x}Mn_xSb-Schichten (bis zum 1% Mangan) auf GaAs (001)-realisiert. Mn verringert die Gitterkonstante und damit den Grad der Relaxation von (In,Mn)Sb-Filmen. In den Proben befindet sich Mn in zwei magnetischen Formen, sowohl als verdünnt-magnetischer Halbleiter (In,Mn)Sb, als auch als MnSb-Cluster. Die Cluster dominieren auf der Oberfläche. Die Curie-Temperatur, Tc, unterscheidet sich für die beiden Formen. Für (In,Mn)Sb ist Tc kleiner als 50 K. Die MnSb-Cluster zeigen dagegen ein Tc über 300 K.This dissertation describes the growth by molecular beam epitaxy and the characterization of the semiconductor InSb and the diluted magnetic semiconductor (DMS) In_{1-x}Mn_xSb. The 2 µm-thick InSb films were grown on GaAs (001) substrate and Si (001) offcut by 4° toward (110) substrate. After optimizing the growth conditions, the best InSb films grown directly on GaAs results in a high crystal quality, low noise, and an electron mobility of 41100 cm^2/V s Vs with associated electron concentration of 2.9e16 cm^{-3} at 300 K. In order to successfully grow InSb on Si, tilted substrates and the insertion of buffer layers were used. An electron mobility of 24000 cm^2/V s measured at 300 K, with an associated carrier concentration of 2.6e16 cm^{-3} is found for the best sample that was grown at 340°C with a 0.06 μm-thick GaSb/AlSb superlattice buffer layer. The sample reveals a density of microtwins and stacking faults as well as threading dislocations in the near-interface. Deep level noise spectra indicate the existence of deep levels in both GaAs and Si-based samples. The Si-based samples exhibit the lowest Hooge factor at 300 K, lower than the GaAs-based samples. Taking the optimized growth conditions of InSb/GaAs, the DMS In_{1-x}Mn_xSb/GaAs is prepared by adding Mn (x < 1%) into the InSb during growth. Mn decreases the lattice constant as well as the degree of relaxation of (In,Mn)Sb films. Mn also distributes itself to result in two different and distinct magnetic materials: the DMS (In,Mn)Sb and clusters MnSb. The MnSb clusters dominate only on the surface. For the DMS alloy (In,Mn)Sb, the measured values of Curie temperature Tc appears to be smaller than 50 K, whereas it is greater than 300 K for the MnSb clusters.
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Freire, Henrique Jota de Paula. "Magneto-transporte e ferromagnetismo Hall em heteroestruturas semicondutoras magnéticas." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-23032007-183322/.
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Heteroestruturas digitais magnéticas (DMHs) são estruturas semicondutoras em que a distribuição de impurezas magnéticas (Mn) restringe-se a alguns arranjos bidimensionais (monocamadas) regularmente espaçados entre si. Na presença de um campo magnético, a interação de troca sp-d entre os momentos magnéticos localizados e os portadores itinerantes é responsável por um desdobramento de spin gigante, da ordem ou até superior que a separação cíclotron dos níveis de Landau. Aqui eu calculo a estrutura eletrônica de poços quânticos digitais magnéticos do grupo II-VI. Resolvo as equações de Kohn-Sham da teoria do funcional da densidade dependente de spin na aproximação de massa efetiva. Eu então calculo diversas propriedades magnetoópticas e de transporte relevantes experimentalmente. Em particular, eu investigo a física dependente de spin presente nestes sistemas sob dois diferentes pontos de vista. Primeiramente o enfoque é no efeito do magnetismo do Mn sobre o potencial dependente de spin da interação de troca sp-d, em particular nos efeitos da aglomeração antiferromagnética e da diluição do seu perfil de concentração (segregação e interdifusão). Ao considerar estes efeitos eu reproduzo resultados experimentais para desdobramento de spin $Delta_E$ e tempos de espalhamento de spin $tau_$ [S. A. Crooker et al., Phys. Rev. Lett. 75, 505 (1995); Phys. Rev. B 61, 1736 (2000)]. Na segunda parte eu mudo o enfoque para a física de gases de elétrons bidimensionais (2DEGs) altamente polarizados e mostro a importância da forte dependência de spin das contribuições de muitos corpos (troca e correlação) presentes nestes sistemas. Em particular, estes efeitos são relevantes para o surgimento de fases de ferromagnetismo de efeito Hall quântico. Eu calculo o magnetotransporte no regime de efeito Hall quântico para DMHs baseadas em ZnSe e CdTe. Meus resultados reproduzem resultados experimentais [R. Knobel et al., Phys. Rev. B 65, 235327 (2002); J. Jaroszynski et al., Phys. Rev. Lett. 89, 266802 (2002)] para a dependência com o campo magnético, com a temperatura, o aparecimento de picos anômalos e o surgimento de curvas de histerese em várias propriedades físicas.Digital magnetic heterostructures (DMHs) are semiconductor structures with magnetic impurities (Mn) restricted to some planar arrangements (monolayers) regularly spaced. In the presence of an external magnetic field, the sp-d exchange interaction between the localized magnetic moments and the itinerant carriers is responsible for a giant spin splitting, of the order of, or even greater than, the cyclotron separation between Landau levels. Here I calculate the electronic structure of group II-VI digital magnetic quantum wells. I solve the Kohn-Sham equations of the spin-density functional theory within the effective mass approximation. Then I calculate some magneto-optical and transport properties which are experimentally relevant. In particular, I investigate the spin dependent physics of these systems from two different points of view. First, I focus on effects of the Mn magnetism on the sp-d exchange spin dependent potential, particularly the effect of antiferromagnetic clustering and the effect of dilution (segregation and interdiusion) of the Mn content prole. By considering these effects I reproduce experimental results for the spin splitting $Delta_E$ and spin scattering times $tau_$ [S. A. Crooker et al., Phys. Rev. Lett. 75, 505 (1995); Phys. Rev. B 61, 1736 (2000)]. In the second part I move on to the physics of spin-polarized two-dimensional electron gases (2DEGs), and show the relevance of the strong dependence of the many-body contributions (exchange and correlation) with the spin polarization. In particular, these effects are relevant for the development of quantum Hall ferromagnetic phases. I calculate magneto- transport in the quantum Hall eect regime for DMHs consisting of ZnSe and CdTe. My results reproduce experimental results [R. Knobel et al., Phys. Rev. B 65, 235327 (2002); J. Jaroszynski et al., Phys. Rev. Lett. 89, 266802 (2002)] for the dependence with magnetic eld, temperature, development of anomalous resistivities spikes and hysteretic behaviors in many physical properties.
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Horsfall, Alton Barrett. "Electrical and magnetic properties of II-VI diluted magnetic semiconductors." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4984/.
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The electrical and magnetic properties of MOVPE grown epitaxial layers of Hg(_1-x)Mn(_x)Te layers has been investigated using a number of techniques. The samples have been grown by the Inter Diffused Multilayer Process, (IMP) on (100) semi insulating GaAs substrates with ZnTe and CdTe buffer layers. The samples have been shown to show a number of phenomena nopt observed in the bulk material, such as an anomaly in the resistivity, rnagnetoresistance related to the intrinsic magnetism of the material, and saturation of the room temperature magnetisation. In general the samples are of a highly compensated nature with the value of |R(_H)e|(^-1) varying between l0(^14) and 5xI0(^17) cm(^-3) at 20K, the Hall mobilities varying between 8 and 3.5x10(^5) cm(^2)V(^-1)s(^-1) at 20K. Magnetically, the samples generally show a paramagnetic signal that is swamped by the diamagnetic background of the substrate and buffer layers. The paramagnetisrn can be well modelled using a Curie Weiss fit. A number of the samples show a saturation in the magnetisation, which, has been explained via the use of vacancy ordering within MnTe regions in the sample. The susceptibility of the samples has been investigated using a Faraday balance system, and this data has been fitted using; a cluster model for Mn ions within the sample. The photomagnetisation of Cd(_0.9)Mn(_0.1)Te:In has been investigated using a faraday balance system, and modelled using the work of Dietl and Sample, to calculate the number of polarons that had formed on donors in the sample, ΔN(_D)(^MAG) = 1.28x10(^15)cm(^-3). The number of donors in the sample has been measured by means of the Hall effect, ΔN(_D)(^ELEC) = 1.92x10(^15)cm(^-3), and this value compared to that obtained from the model. We have proposed a model to explain this discrepancy based on the concept of band tails in the impurity band.
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Virot, François. "Etude théorique de matériaux pour la spintronique." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4816/document.
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Ce mémoire présente les travaux réalisés durant ces trois années de thèse. Ils se sont orientés autour de l'étude des propriétés électroniques et magnétiques des matériaux pour la spintronique. Ce domaine d'avenir doit encore trouver les matériaux adaptés qui permettraient de réaliser les concepts liés à la spintronique. Nos résultats sont les suivants. Nous avons proposé un nouveau modèle qui décrit l'arrangement magnétique dans les couches minces ferromagnétiques possédant une anisotropie uniaxiale. Le modèle apporte une meilleure description des largeurs de domaine en fonction de l'épaisseur ainsi qu'une bonne estimation de l'épaisseur critique à partir de laquelle les domaines de Weiss ne sont plus stables. L'ensemble d'équations en unité réduite découlant du modèle apporte quant à lui un outil supplémentaire aux expérimentateurs. L'étude ab-Initio fait sur les semi-Conducteurs magnétiques dilués à mis en évidence l'importance de la corrélation forte et de l'effet Jahn-Teller dans les matériaux tel que le (Ga,Mn)N et le (Zn,Cr)S. Ces calculs confirment l'ensemble des données expérimentales existantes sur le (Ga,Mn)N. La modélisation analytique apporte un complément aux calculs ab-Initio en faisant le lien entre les paramètres expérimentaux et la théorie de Vallin, très largement utilisée pour interpréter les mesures optiques du (Zn,Cr)S. Nos calculs ab-Initio ont montré que le métacinabre est un isolant topologique robuste, qui se distingue par la présence d'un cône de Dirac extrêmement anisotrope. Les effets de passivation à l'hydrogène influencent les états de surface des isolants topologiques de la série HgX (X : S, Se, Te)This thesis contains the scientific work of three years. The main topic can be defined as follows : study of electronic and magnetic properties of materials for spintronics. That technology of the future has still to find the necessary materials to realize new concepts. Our results are the following : We propose a new model to describe the magnetic configuration in thin ferromagnetic film with uniaxial anisotropy. It gives a better description of domain widths in function of film thickness and permits to obtain a good evaluation of the critical thickness where domains of Weiss type are no longer stable. The set of equations in reduced units is a useful tool to analyze experimental data. The ab-Initio study of diluted magnetic semiconductors has demonstrated the combined effect of strong correlations and Jahn-Teller distortion in (Ga,Mn)N and (Zn,Cr)S. The calculations confirm the experimental results of (Ga,Mn)N. We develop an analytical model that is complementary to the ab-Initio calculations and permits to create a link between several experimental parameters, the ab-Initio calculations and the former theory of Vallin. It has been used to interpret the optical measurements of (Zn,Cr)S. Our ab-Initio studies show that metacinnabar is a strong topological insulator with one peculiarity, it has a highly anisotropic Dirac cone. The passivation with hydrogen atoms influences the surface states of the topological insulator in the series HgX (X : S, Se, Te). When the dangling bonds are saturated by hydrogen, the trivial surface states disappear
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Rajaram, Rekha. "Study of magnetism in dilute magnetic semiconductors based on III-V nitrides /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Ali, Bakhtyar. "Study of titanium dioxide based dilute magnetic semiconductors the role of defects and dopants /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 85 p, 2008. http://proquest.umi.com/pqdweb?did=1597633311&sid=20&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Freeman, Adam Alexander. "Magnetic X-ray spectroscopy studies of dilute magnetic semiconductors." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/10839/.
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Dilute magnetic semiconductors are an important family of materials that have many potential applications in spintronics; (Ga,Mn)As, (In,Ga,Mn)As and (Ga,Mn)N are of major interest. This thesis investigates dierent aspects of these, using the synchrotron radiation techniques of x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD), supported by superconducting quantum interference device (SQUID) magnetometry and magnetotransport measurements. A large anisotropic XMLD signal is observed for the Mn L-edge in (Ga,Mn)As. In unannealed (Ga,Mn)As, an apparently reduced Mn magnetic moment is commonly observed. It is thought to be related to compensation of both carriers and magnetic moment, caused by interstitial Mn. This issue is investigated using combined data from XMCD, XMLD and SQUID magnetometry. The findings suggest that substitutional and interstitial Mn form `non-magnetic' pairs which do not have a preferred spin orientation. (Ga,Mn)N is studied by x-ray absorption and field-dependent XMCD at the Mn L-edge. Two distinct Mn congurations are identified: Mn2+ is prevalent towards the surface with nearly paramagnetic behaviour, while a weakly ferromagnetic Mn2+/Mn3+ mixed valence exists within the bulk. The weak ferromagnetism, often observed in (Ga,Mn)N, is attributed to coupling between the impurities by the double exchange mechanism. Finally, XMCD is used to measure the orbital polarization of As 4p states of (III,Mn)As materials. These states correspond to those of the holes involved in the itinerant exchange interaction in ferromagnetic semiconductors. The coupling between the localized d states of the magnetic impurities and the valence band p states of the host is demonstrated by an anisotropy in the orbital moment of these states. This is experimental confirmation of the origin of the magnetocrystalline anisotropy in dilute magnetic semiconductors.
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Miao, Jingqi. "The theory of magnetic polarons and magnetic field effect in diluted magnetic semiconductors." Thesis, University of Hull, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264955.
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Brieler, Felix [Verfasser]. "Nanostructured diluted magnetic semiconductors within mesoporous silica / Felix Brieler." Gießen : Universitätsbibliothek, 2012. http://d-nb.info/1063954878/34.
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Harley, Eric Chad Toppin McNeil Laurie Elizabeth. "Magneto-optical spectroscopy of dilute magnetic semiconductors." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2006. http://dc.lib.unc.edu/u?/etd,402.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2006.Title from electronic title page (viewed Oct. 10, 2007). " ... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics & Astronomy." Discipline: Physics and Astronomy; Department/School: Physics and Astronomy.
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Owen, Man Hon Samuel. "Electrical gating effects on the magnetic properties of (Ga,Mn)As diluted magnetic semiconductors." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/228705.
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The aim of the research project presented in this thesis is to investigate the effects of electrostatic gating on the magnetic properties of carrier-mediated ferromagnetic Ga1-xMnxAs diluted magnetic semiconductors. (Ga,Mn)As can be regarded as a prototype material because of its strong spin-orbit coupling and its crystalline properties which can be described within a simple band structure model. Compressively strained (Ga,Mn)As epilayer with more complex in-plane competing cubic and uniaxial magnetic anisotropies is of particular interest since a small variation of these competing anisotropy fields provide a means for the manipulation of its magnetization via external electric field. An all-semiconductor epitaxial p-n junction field-effect transistor (FET) based on low-doped Ga0.975Mn0.025As was fabricated. It has an in-built n-GaAs back-gate, which, in addition to being a normal gate, enhances the gating effects, especially in the depletion of the epilayer, by decreasing the effective channel thickness by means of a depletion region. A shift in the Curie temperature of ~2 K and enhanced anisotropic magnetoresistance (AMR) (which at saturation reaches ~30%) is achieved with a depletion of a few volts. Persistent magnetization switchings with short electric field pulses are also observed. The magnitude of the switching field is found to decrease with increasing depletion of the (Ga,Mn)As layer. By employing the k . p semiconductor theory approach (performed by our collaborators in Institute of Physics, ASCR, Prague), including strong spin-orbit coupling effects in the host semiconductor valence band, a change in sign of Kc at hole density of approximately 1.5x1020 cm-3 is observed. Below this density, the [110]/[1⁻10] magnetization directions are favoured, consistent with experimental data. A double-gated FET, with an ionic-gel top-gate coupled with a p-n junction back-gate based on the same material, was also employed in an attempt to achieve larger effects through gating. It reaffirms the results obtained and demonstrates enhanced gating effects on the magnetic properties of (Ga,Mn)As.
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Cheng, Ching-Yun, and 鄭憬筠. "Spin-wave Relaxation in Diluted Magnetic Semiconductor." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/57543954430007304682.
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碩士國立清華大學
物理學系
95
The Self-consistent Green's function method satis‾es Goldstone's theorem and preserves spin kinematics, whereas mean-field theory does not satisfy Goldstone's theory which predicts gapless spin-wave excitation, and the independent spin-wave theory using Holstein-Primakov boson (HP boson) in path integral formulism fails to preserve spin kinematics. The dilute impurity limit provides the nice translational invariance and allowing Fourier transform. Random Phase Approximation(RPA) lowers the order of Green's function and therefore the spin-wave Green's function can be extracted from two equations of motion. In isotropic coupling case, we've found the atypical phenomena of spin-wave lifetime increasing as temperature raises. Obviously, this spectral function narrowing can not due to thermal fluctuation. We then wonder if this awkward behavior comes from quantum fluctuation and whether this would be corrected to match our common sense that lifetime shortens at higher temperature when anisotropy being introduced, in other words, quantum fluctuation being suppressed. It turns out that neither thermal nor quantum fluctuation is to blame on the trend of the increase of spin-wave lifetime at high temperature. And at the same time we are also eager to look for experimental evidence that'll support our prediction.
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郭佳佳. "Fabrication of the diluted magnetic semiconductor nanowires." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/85532735024772591111.
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Hsu, Chen-Feng, and 徐振峰. "Fabrication of the (Ga.Ni)N Diluted Magnetic Semiconductor." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/vm58j2.
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Chakraborti, Deepayan. "Novel diluted magnetic semiconductor materials based on Zinc Oxide." 2007. http://www.lib.ncsu.edu/theses/available/etd-11172007-141719/unrestricted/etd.pdf.
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