Relevant bibliographies by topics / HEISENBERG MODEL; SPIN / Dissertations / Theses
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Dissertations / Theses on the topic 'HEISENBERG MODEL; SPIN'

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Published: 4 June 2021
Last updated: 1 February 2022

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1

Lozano, Dairon Andrés Jiménez. "Modelo de Heisenberg Antiferromagnético de spin-1/2 na rede triangular com interações competitivas." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-21092016-212043/.

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Nesta dissertação estudamos sistemas de spins em redes de baixa dimensionalidade e em temperatura nula, analisando suas transições de fases quânticas. Mais precisamente, estu- damos as propriedades do estado fundamental e as possíveis transições de fase do modelo de Heisenberg quântico antiferromagnético de spin-1/2, com interações entre os primeiros e segundos vizinhos, em diversas redes, e em particular na rede triangular, que é o foco de nosso estudo. Para a obtenção do estado fundamental aproximado, usamos um método variacional em que a rede é particionada num conjunto de plaquetas de síti
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Fong, Manson Cheuk-Man. "Heisenberg model with spin anisotropy on the Kagomé lattice /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202008%20ZFONG.

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Rowan, David Glenn. "Theoretical studies of disordered short-range spin models." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299226.

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4

Szàllàs, Attila. "Heisenberg antiferromagnetic model on 2D quasiperiodic tilings." Paris 11, 2008. http://www.theses.fr/2008PA112174.

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Le pavage de Penrose est une structure quasipériodique bidimensionnelle, utilisée dans la description des composés quasicristallins. Cette structure est parfaitement ordonnée, avec une symétrie de rotation cinq et elle est invariante sous un changement d'échelle par un facteur τ. Nous avons étudié les propriétés d'un modèle d'Heisenberg sur le pavage de Penrose construit à partir de losanges, en utilisant une méthode de développement en ondes de spin. Les énergies et fonctions d'ondes des magnons (quantum d'une onde des spins) ont été étudiées dans le cadre d'une théorie linéarisée. Les propri
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5

Oliveira, Ravenna Rodrigues. "Modelo de Heisenberg para cadeia de spins." reponame:Repositório Institucional da UFC, 2016. http://www.repositorio.ufc.br/handle/riufc/19729.

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OLIVEIRA, R. R. Modelo de Heisenberg para cadeia de spins. 2016. 58 f. Dissertação (Mestrado em Física) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2016.<br>Submitted by Giordana Silva (giordana.nascimento@gmail.com) on 2016-09-26T18:55:18Z No. of bitstreams: 1 2016_dis_rroliveira.pdf: 2847981 bytes, checksum: edaf4ac09f696a3c00730658e00f0e9c (MD5)<br>Approved for entry into archive by Giordana Silva (giordana.nascimento@gmail.com) on 2016-09-26T18:55:56Z (GMT) No. of bitstreams: 1 2016_dis_rroliveira.pdf: 2847981 bytes, checksum: edaf4ac09f696a3c00730658e00f0e9c (MD5)<br>M
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Silva, Wanêssa Façanha da. "Ondas de spin em redes decoradas." reponame:Repositório Institucional da UFC, 2014. http://www.repositorio.ufc.br/handle/riufc/13700.

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SILVA, Wanêssa Façanha. Ondas de spin em redes decoradas. 2014. 62 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014.<br>Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-10-22T20:40:26Z No. of bitstreams: 1 2014_dis_wfsilva.pdf: 5621741 bytes, checksum: 74eb09424ba24b6a3b1acd4b7df5dee6 (MD5)<br>Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-10-22T20:40:38Z (GMT) No. of bitstreams: 1 2014_dis_wfsilva.pdf: 5621741 bytes, checksum: 74
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Souza, Fabiano Caetano de. "Método de diagonalização iterativa para o modelo de Heisenberg." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-13092010-103541/.

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Nesta tese desenvolvemos um método numérico para diagonalizar o Hamiltoniano de Heisenberg iterativamente. O método consiste basicamente em diagonalizar cadeias de spins, cada vez maiores, em que cada passo da diagonalização corresponde à adição de um novo spin à cadeia. A base de vetores para calcular o Hamiltoniano de uma cadeia de N spins, HN, é construída por meio do produto direto dos autovetores do Hamiltoniano Hn-1 da rede diagonalizada no passo anterior, pelos autoestados correspondentes ao N-ésimo spin adicionado. Além de usar a comutação do Hamiltoniano com a componente azimutal do s
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8

Silva, WanÃssa FaÃanha da. "Ondas de spin em redes decoradas." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12439.

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Sistema de baixa dimensionalidade tÃm atraÃdo uma grande atenÃÃo ultimamente devido a sistemas como grafeno e nanotubos de carbono. Tais sistemas tÃm grandes possibilidades de aplicaÃÃes tecnolÃgicas, em particular na criaÃÃo de dispositivos eletrÃnicos, devido Ãs suas propriedades eletrÃnicas especÃficas. Nesse sentido, o estudos de outros sistemas em baixa dimensÃo se torna urgente. Mais especificamente, o estudo de propriedades magnÃticas de materiais de materiais em baixa dimensionalidade tambÃm trÃs grandes novidades no comportamento de sistemas ferromagnÃticos. O comportamento de ondas d
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9

Exler, Matthias. "On classical and quantum mechanical energy spectra of finite Heisenberg spin systems." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980110440.

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10

Szallas, Attila. "Heisenberg antiferromagnetique model sur le pavage quasicrystaux bidimensionnelle." Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00358251.

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Le pavage de Penrose est une structure quasipériodique bidimensionnelle, utilisée dans la description des composés quasicristallins. Cette structure est parfaitement ordonnée, avec une symétrie de rotation cinq et elle est invariante sous un changement d'échelle par un facteur $\tau$ (le nombre d'or). On s'attend à ce que les propriétés d'un modèle d'antiferromagnétisme dans un tel système diffèrent nettement de celles des antiferromagnétiques périodiques. Nous avons étudié les propriétés d'un modèle d'Heisenberg sur le pavage de Penrose construit à partir de losanges, en utilisant une méthode
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Belo, Leandro Ribeiro Andrade. "Modelo de Heisenberg em um espaço com curvatura negativa: excitações topológicas de spin na pseudo-esfera." Universidade Federal de Viçosa, 2007. http://locus.ufv.br/handle/123456789/4263.

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Made available in DSpace on 2015-03-26T13:35:20Z (GMT). No. of bitstreams: 1 texto completo.pdf: 763296 bytes, checksum: 67a8dbb32f0cc3ff0e3104d5ec7126e0 (MD5) Previous issue date: 2007-03-01<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Heisenberg-like spins lying on the pseudosphere (a 2- dimensional infinite space with constant negative curvature) cannot give rise to stable soliton solutions. Only fractional solutions can be stabilized on this surface provided that at least one hole is incorporated. We also address the issue of in-plane vortices, in the XY regime. In
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Fernandes, Walney Reis. "Modelos de emparelhamento integráveis." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-21102010-121332/.

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O objetivo deste trabalho foi o estudo do Ansatz de Bethe Algébrico (ABA), que é uma técnica utilizada na obtenção dos auto-estados do hamiltoniano de inúmeros modelos da Mecânica Estatística e da Teoria Quântica de Campos. Aplicamos este procedimento na diagonalização de três modelos de spins: o modelo de Heisenberg, o modelo de Heisenberg-Sklyanin e o modelo de Heisenberg-Cherednik. Na diagonalização do primeiro modelo, não foi possível encontrar todos os auto-estados do hamiltoniano através do ABA e, durante o procedimento de obtenção das expressões analíticas, nos deparamos com um conjunto
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13

Shinjo, Kazuya. "Density-matrix renormalization group study of quantum spin systems with Kitaev-type anisotropic interaction." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215292.

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14

Janson, Oleg. "DFT-based microscopic magnetic modeling for low-dimensional spin systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-91976.

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In the vast realm of inorganic materials, the Cu2+-containing cuprates form one of the richest classes. Due to the combined effect of crystal-field, covalency and strong correlations, all undoped cuprates are magnetic insulators with well-localized spins S=1/2, whereas the charge and orbital degrees of freedom are frozen out. The combination of the spin-only nature of their magnetism with the unique structural diversity renders cuprates as excellent model systems. The experimental studies, boosted by the discovery of high-temperature superconductivity in doped La2CuO4, revealed a fascinating v
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15

Antini, Alessandro. "Non-local order parameters in one-dimensional spin systems." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18043/.

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Per molti anni si è creduto che la teoria di Landau sulla rottura spontanea di simmetria esaurisse la descrizione di tutte le fasi in cui è possibile osservare la materia. Ogni transizione di fase si riteneva dunque dover essere sempre accompagnata da un cambiamento della simmetria del sistema. È da diversi decenni ormai che però siamo consapevoli dell'esistenza di fasi della materia distinte che posseggono esattamente la stessa simmetria. A queste fasi è stato dato il nome di fasi topologiche, e chiaramente non possono essere descritte e previste dalla teoria di Landau. In sistemi unidimensio
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16

Sauerwein, Ricardo Andreas. "Método de Monte Carlo para Sistemas Quânticos." Universidade de São Paulo, 1995. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-13122013-180031/.

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As propriedades do estado fundamental do modelo de Heisenberg antiferroinagnético quântico de spin-1/2 na rede quadrada e na rede cúbica espacialmente anisotrópica são investigadas através de um novo método de Monte Carlo, baseado na estimativa do maior autovalor de uma matriz de elementos não negativos. A energia do estado fundamental e a magnetização \"staggered\" destes sistemas são calculadas em redes relativamente grandes com até 24 x 24 sítios para o caso de redes quadradas e 8 x 8 x 8 sítios para o caso de redes cúbicas. O método desenvolvido também pode ser usado como um novo algoritmo
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17

Allalen, Mohammed. "Magnetic properties and proton spin-lattice relaxation in molecular clusters." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979984777.

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18

Schäpers, Markus. "Exploring the Frustrated Spin-Chain Compound Linarite by NMR and Thermodynamic Investigations." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-153947.

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Within the last decades low-dimensional frustrated quantum spin systems have attracted great interest in the field of modern research. In these systems a competition of various magnetic interactions takes place, leading to an energetically degenerated magnetic ground state, and thus to the occurrence of exotic, unconventional physical properties at low temperatures. This thesis focuses on the quasi one-dimensional frustrated spin chain system linarite, PbCuSO4(OH)2. In this compound the basic building blocks are CuO4 plaquettes which are connected to each other along one crystallographic dire
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19

Freire, MÃrcio de Melo. "Teoria de funÃÃes de Green para uma impureza isolada localizada intersticialmente em sistemas ferromagnÃticos." Universidade Federal do CearÃ, 2017. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=18807.

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico<br>Um formalismo da funÃÃo de Green à usado para calcular o espectro de excitaÃÃes associadas com uma impureza magnÃtica localizada intersticialmente em diferentes estruturas ferromagnÃticas descritas pelo modelo de Ising e de Heisenberg. No capÃtulo 3, descrevemos um ferromagneto de rede cÃbica simples semi-infinita atravÃs do modelo de Ising. Neste caso, as excitaÃÃes nÃo-ressonantes (isto Ã, os modos de defeito fora da regiÃo das ondas de spin de volume e de superfÃcie) e as excitaÃÃes ressonantes (os modos de defeito dentro da r
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Canals, Benjamin. "Contribution à l'étude des propriétés de quelques systèmes magnétiques frustrés." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10142.

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Nous etudions trois reseaux frustres geometriquement. En utilisant l'hamiltonien de heisenberg quantique antiferromagnetique sur le reseau pyrochlore, nous donnons des arguments qui caracterisent ce systeme comme un liquide de spins ou le gap est tres faible. Les delafossites dopes (la,y)cuo#2#. #6#6 sont interpretes comme des reseaux kagome. En considerant differents modeles (xy, hubbard, t-j), nous concluons que le compose au lanthane est certainement metallique alors que celui a l'yttrium doit etre isolant. Nous caracterisons dans les deux cas (la ou y) les proprietes magnetiques. Enfin, le
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Chaboussant, Grégory. "Étude expérimentale d'une échelle de spin-1/2 antiferromagnétique : Cu2(C5H12N2)2Cl4." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10007.

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Ce memoire presente une etude experimentale d'un compose organique isolant ayant des proprietes magnetiques unidimensionnelles (1d): cu#2(c#5h#1#2n#2)#2cl#4. C'est un systeme antiferromagnetique de heisenberg s=1/2 en echelle de spins. Les interactions d'echanges entre les electrons non apparies des ions cu#2#+ forment une structure magnetique en echelle que l'on peut decrire par deux parametres d'echanges, j entre les barreaux et j le long des deux chaines. Comme toutes les echelles de spin-1/2 ayant un nombre pair de chaines couplees, ce systeme a un gap d'energie dans le spectre des excitat
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22

Grechnyev, Oleksiy. "Theoretical Studies of Two-Dimensional Magnetism and Chemical Bonding." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4815.

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23

Labouze, Xavier. "Etude par résonances nucléaires des propriétés magnétiques des cuprates supraconducteurs dans leurs phases isolantes." Grenoble 1, 1994. http://www.theses.fr/1994GRE10042.

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Cette these porte sur l'etude des proprietes magnetiques des cuprates supraconducteurs dans leurs phases isolantes. Les techniques experimentales utilisees sont la resonance nucleaire, magnetique (rmn) et quadrupolaire (rqn). La premiere partie presente une revue des proprietes essentielles des cuprates supraconducteurs. La deuxieme explique particulierement comment utiliser la rqn. L'etude des composes au plomb type ybco (partie iii) montre que le magnetisme des cuprates doit etre quasi-2d quasi-heisenberg. La partie iv traite des composes ybco substitues au calcium. L'etude statique par mesu
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Beaujouan, David. "Simulation des matériaux magnétiques à base Cobalt par Dynamique Moléculaire Magnétique." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00760645.

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Les propriétés magnétiques des matériaux sont fortement connectées à leur structure cristallographique. Nous proposons un modèle atomique de la dynamique d'aimantation capable de rendre compte de cette magnétoélasticité. Bien que ce travail s'inscrive dans une thématique générale de l'étude des matériaux magnétiques en température, nous la particularisons à un seul élément, le Cobalt. Dans ce modèle effectif, les atomes sont décrits par 3 vecteurs classiques qui sont position, impulsion et spin. Ils interagissent entre eux via un potentiel magnéto-mécanique ad hoc. On s'intéresse tout d'abord
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Rosner, Helge. "Electronic structure and exchange integrals of low-dimensional cuprates." [S.l. : s.n.], 1999. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9470690.

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26

Collins, Alexander Rory Physics Faculty of Science UNSW. "Quantum lattice models." Publisher:University of New South Wales. Physics, 2008. http://handle.unsw.edu.au/1959.4/43408.

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This thesis presents studies of the low energy properties of nseveral frustrated spin-1/2 Heisenberg antiferromagnets using various analytic and computational methods. The models studied include the union jack model, the alternating Heisenberg chain, the Heisenberg bilayer model, and the spin-Peierls model. The union jack model is a Heisenberg antiferromagnetic spin model with frustration, and is analyzed using spin-wave theory. For small values of the frustrating coupling $\alpha$, the system is N{\' e}el ordered, while for large $\alpha$ the frustration is found to induce a canted phase. Spi
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Nunes, Wagner Antonio da Silva. "Comportamento multicrítico no modelo de Heisenberg frustrado: transições de fases clássica e quântica." Universidade Federal de São Carlos, 2011. https://repositorio.ufscar.br/handle/ufscar/4970.

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Made available in DSpace on 2016-06-02T20:15:30Z (GMT). No. of bitstreams: 1 5740.pdf: 4504584 bytes, checksum: 51970950add8aab7bab613ecfd4117ee (MD5) Previous issue date: 2011-09-01<br>In this work we study the critical behavior of systems described by the Anysotropic- Heisenberg model of spin 1/2 with competitive interactions (J1-J2 Model) on planes, and interplane nearest-neighbor interactions. We applied Effective-Field techniques for finite clusters with two (EFT2) and four (EFT4) central sites, as well as Linear Spin-Waves Theory (LSWT). We define &#945;=J2/J1, as the frustration param
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Goomanee, Salvish. "Rigorous Approach to Quantum Integrable Models at Finite Temperature." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEN039/document.

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Cette thèse développe un cadre rigoureux qui permet de démontrer des représentations exactes associées à divers observables de la chaîne XXZ de Heisenberg de spin 1/2 à température finie. Il a était argumenté dans la littérature que l’énergie libre par site ou les longueurs de corrélations admettent des représentations intégrales où les intégrandes sont exprimées en termes de solutions d’équations intégrales non-linéaires. Les dérivations de ces représentations reposaient sur divers conjectures telles que l’existence d’une valeur propre de la matrice de transfert quantique, real, non-dégénérée
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Litaiff, Fabian Cardoso. "Modelos de spins geometricamente frustrados: transição de fase e estruturas de platores." Universidade Federal de São Carlos, 2013. https://repositorio.ufscar.br/handle/ufscar/4963.

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Made available in DSpace on 2016-06-02T20:15:29Z (GMT). No. of bitstreams: 1 5202.pdf: 3904832 bytes, checksum: c623a581c3cdb03d9cc81fc16ecef935 (MD5) Previous issue date: 2013-04-08<br>Universidade Federal de Minas Gerais<br>This thesis presents a study of the magnetization plateau and the phenomenon of geometrical frustration in spin systems applied to lattices with triangular structure, as well as the results achieved by applying the differential operator technique of the Ising and Heisenberg models with external magnetic field applied to the easy magnetization axis z, their phase diagram
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Favaro, Ana Paula. "Energia do estado fundamental de modelo de Heisenberg para cadeias de spin com ligações alternadas e com defeitos locais." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-25082015-114253/.

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Estudamos modelos de materiais magnéticos não uniformes, ou seja, sem simetria translacional. Esta simetria pode ser quebrada pela bordas do sistema, e pela presença de impurezas ou defeitos, ou reduzida por modulações periódicas nas ligações. Como ferramenta nessas investigações utilizamos a formulação da Teoria do Funcional da Densidade para o modelo de Heisenberg. Baseados nos conceitos dessa formulação, propomos a aproximação de ligação local. com o intuito de prover uma forma viável para calcular a energia do estado fundamental de uma cadeia de spins com defeitos ou com modulações nas lig
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Caprara, Leandro Peres. "Ondas de spin em paredes de domínio unidimensionais em monocamadas magnéticas." Universidade Federal de São Carlos, 2012. https://repositorio.ufscar.br/handle/ufscar/5043.

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Made available in DSpace on 2016-06-02T20:16:49Z (GMT). No. of bitstreams: 1 4517.pdf: 1547785 bytes, checksum: 6effb94c4a1e222fb3264328e57ccfc6 (MD5) Previous issue date: 2012-08-16<br>Financiadora de Estudos e Projetos<br>Recent investigations on ferromagnetic monolayers predict the existence of spinwave modes without gap in the spectrum, even in the presence of anisotropy. These excitations propagate within the domain walls that exist in the monolayer, hence in quasione- dimensional structures. They are different from the known bulk-modes whose spectrum presents anisotropy gap and whose p
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Santos, Marcelo Meireles dos. "A evolução temporal de sistemas de spins 1/2 congelados no espaço e descritos pelo modelo de Heisenberg." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-27032013-120632/.

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Este projeto se destina ao estudo de sistemas quânticos não relativísticos de dois, quatro e oito níveis de energia que descrevem partículas com spin s=1/2 sujeitas à ação de campos externos e interagentes entre si. São apresentadas soluções exatas para as equações que regem esses sistemas. Tais sistemas possuem uma vasta aplicação em diversas áreas da física, dentre as quais é possível destacar a computação quântica. Possíveis aplicações dos resultados são a construção de portas lógicas quânticas universais. Estas portas lógicas quânticas representam um elemento essencial no desenvolvimento d
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Campos, Alessandra Matos. "Implementações sequencial e paralela de um novo algoritmo para a simulação de elementos e compostos magnéticos." Universidade Federal de Juiz de Fora (UFJF), 2011. https://repositorio.ufjf.br/jspui/handle/ufjf/3543.

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Freire, Márcio de Melo. "Teoria de funções de Green para uma impureza isolada localizada intersticialmente em sistemas ferromagnéticos." reponame:Repositório Institucional da UFC, 2017. http://www.repositorio.ufc.br/handle/riufc/22443.

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FREIRE, M. de M. Teoria de funções de Green para uma impureza isolada localizada intersticialmente em sistemas ferromagnéticos. 2017. 140 f. Tese (Doutorado em Física) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2017.<br>Submitted by Giordana Silva (giordana.nascimento@gmail.com) on 2017-04-03T22:07:25Z No. of bitstreams: 1 2017_tese_mdmfreire.pdf: 7628225 bytes, checksum: e3a2dea720868776f72333124b7437b6 (MD5)<br>Approved for entry into archive by Giordana Silva (giordana.nascimento@gmail.com) on 2017-04-03T22:08:00Z (GMT) No. of bitstreams: 1 2017_tese_mdmfreire.pdf: 7628
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Mei, Zhongtao. "Wave Functions of Integrable Models." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1530880774625297.

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36

Abreu, Anne Beatriz Rocha. "Teoria quântica de campos aplicada em Modelos de Spins Frustrados." Universidade Federal do Amazonas, 2013. http://tede.ufam.edu.br/handle/tede/4548.

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Submitted by Geyciane Santos (geyciane_thamires@hotmail.com) on 2015-08-06T15:26:04Z No. of bitstreams: 1 Dissertação - Anne Beatriz Rocha Abreu.pdf: 1366448 bytes, checksum: 47c7b96a4f310e46ae8f497afc56d8cb (MD5)<br>Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-08-07T13:52:03Z (GMT) No. of bitstreams: 1 Dissertação - Anne Beatriz Rocha Abreu.pdf: 1366448 bytes, checksum: 47c7b96a4f310e46ae8f497afc56d8cb (MD5)<br>Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-08-07T13:54:2
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Dillenschneider, Raoul. "Effets d'une contrainte d'occupation strictedans la description de systemes de spins quantiquesa temperature finie." Phd thesis, Université Louis Pasteur - Strasbourg I, 2006. http://tel.archives-ouvertes.fr/tel-00129129.

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Nous etudions des systemes de spin quantiques a temperature finie<br />avec une contrainte d'occupation stricte des sites au moyen d'une procedure<br />introduite par V. N. Popov et S. A. Fedotov. Nous montrons que cette contrainte modifie <br />le comportement d'observables physiques par rapport au cas ou cette<br />contrainte est fixee de facon moyenne par la methode des multiplicateurs de Lagrange. La pertinence de l'etat de Neel est <br />etudiee en presence de la contrainte stricte d'occupation des sites du <br />reseau de spin. <br />La temperature de transition des parametres d'ordre an
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38

Keller-Marxer, Peter. "The antiferromagnetic square-lattice O(3) quantum Heisenberg model for spins S = 1/2 - 5/2 at low temperatures : confirmation of field-theoretical predictions by quantum Monte Carlo simulation /." [Bern] : [s.n.], 1999. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.

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39

Mondelli, Claudia. "Fluctuations, frustration and dilution in the SrCrxGa(12-x)O19 compounds : neutron scattering investigation in a broad dynamical range." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10250.

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Le compose srcr xga 1 2 xo 1 9 (scgo) represente un bon exemple de systeme magnetique a basse dimensionalite et haute fluctuation. Scgo est un antiferromagnetique de type heisenberg avec de fortes interactions entre premiers voisins ( c w 500k) mais sans ordre a grande distance jusqu'a 100 mk. Les proprietes magnetiques de ce systeme sont associees a l'arrangement d'une majorite de spins de l'ion cr 3 + sur un sous-reseau hautement frustre (le pyrochlore slab) presentant un etat fondamental de type liquide de spin fortement degenere, mais avec certaines proprietes des verres de spin. Les momen
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40

Pouget, Stéphanie. "Contribution à l'étude de l'influence de la dilution sur les propriétés magnétiques de composés isolants frustrés." Toulouse, INSA, 1993. http://www.theses.fr/1993ISAT0039.

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Nous avons principalement etudie le systeme ferromagnetique heisenberg-3d frustre cdcr#2#(#1##x#)in#2#xs#4, dans la limite des faibles dilutions x. La structure des phases ferromagnetiques et verre de spin reentrante a ete exploree par diffraction de neutrons et mesures d'aimantation macroscopiques. Les resultats s'interpretent dans le cadre d'un modele inhomogene du systeme de spins. Par diffusion de neutrons aux petits angles, spectrometries trois-axes et d'echo de spin, nous avons caracterise le comportement critique statique et dynamique des composes x=0 et 0. 05. Cette etude a revele la p
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41

Filor, Stephan. "A Variational Cluster Approximation for the Heisenberg Model." Doctoral thesis, 2016. http://hdl.handle.net/11858/00-1735-0000-0023-3E15-1.

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42

Hsu, De-Bang, and 許德邦. "Ground State Properties of the One-dimensional Uniaxial Single-ion Anisotropic Spin-1 XXZ Heisenberg Model." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/56933258370599519508.

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碩士<br>東海大學<br>物理學系<br>103<br>In this thesis, we investigate the ground state properties of the one-dimensional antiferromagnet Heisenberg model by Exact diagonalization (ED) and Density Matrix Renormalization Group(DMRG). By the exact diagonalization, we calculate the ground state energy and spin correlation function. We employ DMRG to investigate the ground-state phase diagram of the one-dimensional uniaxial single-ion anisotropic Spin-1 XXZ Heisenberg model on different lattice sizes. By the analysis based on the property of symmetry-protected topological order, we obtain the even-Haldane
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43

韓仁傑. "Monte Carlo determination of the low-energy constants — spin wave velocity, spin stiffness and staggered magnetization density —, of the (3+1)-dimensional quantum Heisenberg model." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/995d62.

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44

Shchelokovskyy, Pavlo. "Solitary objects on quantum spin rings." Doctoral thesis, 2004. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2004121610.

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We investigate whether quantum spin rings with nearest-neighbor Heisenberg or Ising exchange interactions can host solitary states. Using complete diagonalization techniques the system is described without classical or semiclassical approximation. In this case definitions used in connection with classical solitons are not applicable, one needs to redefine what solitary objects on a quantum spin system with translational symmetry ought to be. Thus, we start our contribution by defining which quantum states possess solitary character. In addition we discuss useful observables in order to visuali
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Agrapidis, Cliò Efthimia. "Topologically non-trivial states in one- and quasi-one-dimensional frustrated spin systems." Doctoral thesis, 2019. https://tud.qucosa.de/id/qucosa%3A36334.

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Magnetic frustration is a phenomenon arising in spin systems when spin interactions cannot all be satisfied at the same time. A typical example of geometric frustration is a triangle with Ising-spins at its vertices and antiferromagnetic interaction. While we can easily anti-align two neighbouring spins, it is not possible for the third one to simultaneously anti-align with both of them. Another flavour of magnetic frustration is the so called exchange frustration, where different spin components interact in an Ising fashion on different bonds. Moreover, frustrated spin systems give rise to ex
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46

Kalz, Ansgar. "Phase diagrams of two-dimensional frustrated spin systems." Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F080-B.

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Gharakhloo, Roozbeh. "Asymptotic Analysis of Structured Determinants via the Riemann-Hilbert Approach." Thesis, 2019. http://hdl.handle.net/1805/19918.

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Indiana University-Purdue University Indianapolis (IUPUI)<br>In this work we use and develop Riemann-Hilbert techniques to study the asymptotic behavior of structured determinants. In chapter one we will review the main underlying definitions and ideas which will be extensively used throughout the thesis. Chapter two is devoted to the asymptotic analysis of Hankel determinants with Laguerre-type and Jacobi-type potentials with Fisher-Hartwig singularities. In chapter three we will propose a Riemann-Hilbert problem for Toeplitz+Hankel determinants. We will then analyze this Riemann-Hilbert pro
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48

Schnalle, Roman. "Symmetry assisted exact and approximate determination of the energy spectra of magnetic molecules using irreducible tensor operators." Doctoral thesis, 2009. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2009102618.

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In this work a numerical approach for the determination of the energy spectra and the calculation of thermodynamic properties of magnetic molecules is presented. The work is focused on the treatment of spin systems which exhibit point-group symmetries. Ring-like and archimedean-type structures are discussed as prominent examples. In each case the underlying spin quantum system is modeled by an isotropic Heisenberg Hamiltonian. Its energy spectrum is calculated either by numerical exact diagonalization or by an approximate diagonalization method introduced here. In order to implement full spin-
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譚登瑞. "Monte Carlo simulation of 2-d spatially anisotropic spin-1/2 Heisenberg models." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/15566862694079959505.

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Brüger, Mirko. "Anisotropie und Magnetostriktion als Korrekturen zum Heisenberg-Modell am Beispiel des Moleküls {Ni4Mo12}." Doctoral thesis, 2008. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2008092616.

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Das Standart-Modell zur Beschreibung von Observablen magnetischer Moleküle ist das Heisenberg-Modell. In diesem wird der Magnetismus des Superaustausches der Elektronen durch einfache bilineare Spin-Spin-Kopplungen beschrieben. Zur genaueren Approximation experimenteller Ergebnisse können, der jeweiligen Struktur des Moleküls entsprechend, verschiedene Erweiterungen des Heisenberg-Modells verwendet werden. Diese werden, explizit für das 4-Spin-System {Ni4Mo12}, in ihren Auswirkungen auf die Hochtemperatur-Nullfeldsuszeptibilität, die Nullfeldsuszeptibilität und die Hochfeldmagnetisierung betra
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