Modelos magnéticos com frustração e diluição
Autor(a) principal: | |
---|---|
Data de Publicação: | 2006 |
Tipo de documento: | Tese |
Idioma: | por |
Título da fonte: | Repositório Institucional da UFSCAR |
Texto Completo: | https://repositorio.ufscar.br/handle/ufscar/4918 |
Resumo: | In this work, we investigate the effect of dilution and frustration in the thermodynamic properties and the phase diagrams using the quasi-two-dimensional Heisenberg and Ising models. We use the Zubarev Green´s function formalism and obtain the magnetic properties of the quasi-two-dimensional antiferromagnetic spin ½ Heisenberg model. We determine the limit of the stability of the antiferromagnetic phase as a function of the concentration of the holes in the CuO2 plane and dilution of the Cu by Zn. We simulate the point of maximum of the phase diagram in the plane (T,z) following the experimental data for the La2-xSrxCu1-zZnzO4 compounds. In the Heisenberg model the effect of the frustration is simulated by the parameter λ=λ0(1-x/xc), which measures the interaction between the CuO2 planes. The effect of dilution present in the xy-plane is described theoretically by a small value for z through an effective interaction J(1-z) (mean field approach). We extend the present formalism to include long-range interaction in the antiferromagnetic one-dimensional Heisenberg frustrated model and verify the absence of magnetic order for p>1 (where p is the decay interaction parameter, i.e., Jn=J/np). We also study the thermodynamic properties of the quenched decorated diluted Ising model with competitive interactions, using the differential operator technique with the effective field. The decorated Ising model with competitive interactions used is herein to describe the magnetic properties of the copper-oxide plane containing superconductor compounds in the insulating phase (antiferromagnetic). The model consists of planes in which the nodal spins interact antiferromagnetically (JA<0) with their nearest-neighbors, and ferromagnetically (JF>0) with the quenched spins that decorate the bonds (simulating the Cu-O interaction), and distributed randomly over the two-dimensional lattice. The planes interact antiferromagnetically with weak-exchange interaction (i.e., ). Moreover, in our model some magnetic sites (atoms of Cu) are substituted by non-magnetic sites. We study the thermodynamic properties of the system and the limit of antiferromagnetic stability in the phase diagrams (T,p) and (T,z), for some values of the frustration parameter (α= J ' = λ ,λ = 10−5 A A J J A\JF) and magnetic field. We observe for some values α, the system presents a reentrant behavior in low temperatures, which also is reflected in the thermodynamic properties. |
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Pacobahyba, Josefa Teixeira de MendonçaSouza, José Ricardo dehttp://lattes.cnpq.br/0521315770932665bb59ea9b-4cfa-4d91-91cd-c729c907baa32016-06-02T20:15:20Z2009-11-122016-06-02T20:15:20Z2006-12-08PACOBAHYBA, Josefa Teixeira de Mendonça. Modelos magnéticos com frustração e diluição. 2006. 222 f. Tese (Doutorado em Ciências Exatas e da Terra) - Universidade Federal de São Carlos, São Carlos, 2006.https://repositorio.ufscar.br/handle/ufscar/4918In this work, we investigate the effect of dilution and frustration in the thermodynamic properties and the phase diagrams using the quasi-two-dimensional Heisenberg and Ising models. We use the Zubarev Green´s function formalism and obtain the magnetic properties of the quasi-two-dimensional antiferromagnetic spin ½ Heisenberg model. We determine the limit of the stability of the antiferromagnetic phase as a function of the concentration of the holes in the CuO2 plane and dilution of the Cu by Zn. We simulate the point of maximum of the phase diagram in the plane (T,z) following the experimental data for the La2-xSrxCu1-zZnzO4 compounds. In the Heisenberg model the effect of the frustration is simulated by the parameter λ=λ0(1-x/xc), which measures the interaction between the CuO2 planes. The effect of dilution present in the xy-plane is described theoretically by a small value for z through an effective interaction J(1-z) (mean field approach). We extend the present formalism to include long-range interaction in the antiferromagnetic one-dimensional Heisenberg frustrated model and verify the absence of magnetic order for p>1 (where p is the decay interaction parameter, i.e., Jn=J/np). We also study the thermodynamic properties of the quenched decorated diluted Ising model with competitive interactions, using the differential operator technique with the effective field. The decorated Ising model with competitive interactions used is herein to describe the magnetic properties of the copper-oxide plane containing superconductor compounds in the insulating phase (antiferromagnetic). The model consists of planes in which the nodal spins interact antiferromagnetically (JA<0) with their nearest-neighbors, and ferromagnetically (JF>0) with the quenched spins that decorate the bonds (simulating the Cu-O interaction), and distributed randomly over the two-dimensional lattice. The planes interact antiferromagnetically with weak-exchange interaction (i.e., ). Moreover, in our model some magnetic sites (atoms of Cu) are substituted by non-magnetic sites. We study the thermodynamic properties of the system and the limit of antiferromagnetic stability in the phase diagrams (T,p) and (T,z), for some values of the frustration parameter (α= J ' = λ ,λ = 10−5 A A J J A\JF) and magnetic field. We observe for some values α, the system presents a reentrant behavior in low temperatures, which also is reflected in the thermodynamic properties.Neste trabalho investigamos os efeitos de diluição e frustração nas propriedades termodinâmicas e os diagramas de fase nos modelos de Heisenberg e Ising quase-bidimensional. Usamos o formalismo das funções de Green de Zubarev e obtivemos as propriedades magnéticas do modelo de Heisenberg antiferromagnético quasebidimensional de spin ½. Determinamos o limite de estabilidade da fase antiferromagnética em função da concentração dos buracos no plano CuO2 e da diluição do Cu pelo Zn. Simulamos o ponto de máximo do diagrama de fase no plano (T,z) previsto experimentalmente para o composto La2-xSrxCu1-zZnzO4. No modelo de Heisenberg o efeito da frustração é simulado pelo parâmetro λ=λ0(1-x/xc), medindo a interação entre os planos de CuO2. O efeito da diluição que está presente no plano xy é teoricamente descrito fenomenologicamente para pequeno valor de z através de uma interação efetiva J(1-z) (aproximação tipo campo médio). Estendemos o presente formalismo para incluir interação de longo alcance no modelo de Heisenberg unidimensional antiferromagnético frustrado e verificamos ausência de ordem magnética para p > 1 (onde p é o parâmetro do decaimento da interação, i.e., Jn = J/np). Estudamos também as propriedades termodinâmicas do modelo de Ising diluído decorado de forma quenched com interações competitivas através da técnica do operador diferencial unida à teoria de campo efetivo. O modelo de Ising decorado com interações competitivas é utilizado para descrever qualitativamente as propriedades termodinâmicas dos compostos supercondutores baseados em planos de cobre-oxigênio na sua fase isolante (antiferromagnética). O modelo consiste de planos nos quais os spins nodais interagem antiferromagneticamente (JA < 0) com seus primeiros vizinhos (simulando a interação Cu-Cu), e ferromagneticamente (JF > 0) com os spins decoradores (simulando a interação Cu-O), os quais são distribuídos aleatoriamente de forma quenched sobre uma rede bidimensional. Os planos interagem antiferromagneticamente com uma fraca interação de troca (i.e., J'A = λJA, λ = 10-5). Além disso, em nosso modelo alguns sítios magnéticos (átomos de Cu) são substituídos por sítios não magnéticos. Discutimos além das propriedades termodinâmicas do sistema o limite de estabilidade antiferromagnética nos diagramas de fase (T,p) e (T,z), para vários valores do parâmetro de frustração (α = JA\JF) e campo magnético. Observamos que certos intervalos de valores de α, o sistema apresenta um comportamento reentrante em baixas temperaturas o que se reflete nas propriedades termodinâmicas.application/pdfporUniversidade Federal de São CarlosPrograma de Pós-Graduação em Física - PPGFUFSCarBRPropriedades magnéticasModelo de HeisenbergModelo de IsingFrustraçãoDiluiçãoCIENCIAS EXATAS E DA TERRA::FISICAModelos magnéticos com frustração e diluiçãoinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/doctoralThesis-1-1af214181-4ec9-4a86-80bb-5ccdb15009f0info:eu-repo/semantics/openAccessreponame:Repositório Institucional da UFSCARinstname:Universidade Federal de São Carlos (UFSCAR)instacron:UFSCARORIGINAL2465.pdfapplication/pdf21103782https://repositorio.ufscar.br/bitstream/ufscar/4918/1/2465.pdfbb2c2dc32243d775d710a3b870a259e7MD51THUMBNAIL2465.pdf.jpg2465.pdf.jpgIM Thumbnailimage/jpeg7333https://repositorio.ufscar.br/bitstream/ufscar/4918/2/2465.pdf.jpg3b046a376512c267fb6bfc4b2be5b0f5MD52ufscar/49182023-09-18 18:31:04.899oai:repositorio.ufscar.br:ufscar/4918Repositório InstitucionalPUBhttps://repositorio.ufscar.br/oai/requestopendoar:43222023-09-18T18:31:04Repositório Institucional da UFSCAR - Universidade Federal de São Carlos (UFSCAR)false |
dc.title.por.fl_str_mv |
Modelos magnéticos com frustração e diluição |
title |
Modelos magnéticos com frustração e diluição |
spellingShingle |
Modelos magnéticos com frustração e diluição Pacobahyba, Josefa Teixeira de Mendonça Propriedades magnéticas Modelo de Heisenberg Modelo de Ising Frustração Diluição CIENCIAS EXATAS E DA TERRA::FISICA |
title_short |
Modelos magnéticos com frustração e diluição |
title_full |
Modelos magnéticos com frustração e diluição |
title_fullStr |
Modelos magnéticos com frustração e diluição |
title_full_unstemmed |
Modelos magnéticos com frustração e diluição |
title_sort |
Modelos magnéticos com frustração e diluição |
author |
Pacobahyba, Josefa Teixeira de Mendonça |
author_facet |
Pacobahyba, Josefa Teixeira de Mendonça |
author_role |
author |
dc.contributor.authorlattes.por.fl_str_mv |
http://lattes.cnpq.br/0521315770932665 |
dc.contributor.author.fl_str_mv |
Pacobahyba, Josefa Teixeira de Mendonça |
dc.contributor.advisor1.fl_str_mv |
Souza, José Ricardo de |
dc.contributor.authorID.fl_str_mv |
bb59ea9b-4cfa-4d91-91cd-c729c907baa3 |
contributor_str_mv |
Souza, José Ricardo de |
dc.subject.por.fl_str_mv |
Propriedades magnéticas Modelo de Heisenberg Modelo de Ising Frustração Diluição |
topic |
Propriedades magnéticas Modelo de Heisenberg Modelo de Ising Frustração Diluição CIENCIAS EXATAS E DA TERRA::FISICA |
dc.subject.cnpq.fl_str_mv |
CIENCIAS EXATAS E DA TERRA::FISICA |
description |
In this work, we investigate the effect of dilution and frustration in the thermodynamic properties and the phase diagrams using the quasi-two-dimensional Heisenberg and Ising models. We use the Zubarev Green´s function formalism and obtain the magnetic properties of the quasi-two-dimensional antiferromagnetic spin ½ Heisenberg model. We determine the limit of the stability of the antiferromagnetic phase as a function of the concentration of the holes in the CuO2 plane and dilution of the Cu by Zn. We simulate the point of maximum of the phase diagram in the plane (T,z) following the experimental data for the La2-xSrxCu1-zZnzO4 compounds. In the Heisenberg model the effect of the frustration is simulated by the parameter λ=λ0(1-x/xc), which measures the interaction between the CuO2 planes. The effect of dilution present in the xy-plane is described theoretically by a small value for z through an effective interaction J(1-z) (mean field approach). We extend the present formalism to include long-range interaction in the antiferromagnetic one-dimensional Heisenberg frustrated model and verify the absence of magnetic order for p>1 (where p is the decay interaction parameter, i.e., Jn=J/np). We also study the thermodynamic properties of the quenched decorated diluted Ising model with competitive interactions, using the differential operator technique with the effective field. The decorated Ising model with competitive interactions used is herein to describe the magnetic properties of the copper-oxide plane containing superconductor compounds in the insulating phase (antiferromagnetic). The model consists of planes in which the nodal spins interact antiferromagnetically (JA<0) with their nearest-neighbors, and ferromagnetically (JF>0) with the quenched spins that decorate the bonds (simulating the Cu-O interaction), and distributed randomly over the two-dimensional lattice. The planes interact antiferromagnetically with weak-exchange interaction (i.e., ). Moreover, in our model some magnetic sites (atoms of Cu) are substituted by non-magnetic sites. We study the thermodynamic properties of the system and the limit of antiferromagnetic stability in the phase diagrams (T,p) and (T,z), for some values of the frustration parameter (α= J ' = λ ,λ = 10−5 A A J J A\JF) and magnetic field. We observe for some values α, the system presents a reentrant behavior in low temperatures, which also is reflected in the thermodynamic properties. |
publishDate |
2006 |
dc.date.issued.fl_str_mv |
2006-12-08 |
dc.date.available.fl_str_mv |
2009-11-12 2016-06-02T20:15:20Z |
dc.date.accessioned.fl_str_mv |
2016-06-02T20:15:20Z |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/doctoralThesis |
format |
doctoralThesis |
status_str |
publishedVersion |
dc.identifier.citation.fl_str_mv |
PACOBAHYBA, Josefa Teixeira de Mendonça. Modelos magnéticos com frustração e diluição. 2006. 222 f. Tese (Doutorado em Ciências Exatas e da Terra) - Universidade Federal de São Carlos, São Carlos, 2006. |
dc.identifier.uri.fl_str_mv |
https://repositorio.ufscar.br/handle/ufscar/4918 |
identifier_str_mv |
PACOBAHYBA, Josefa Teixeira de Mendonça. Modelos magnéticos com frustração e diluição. 2006. 222 f. Tese (Doutorado em Ciências Exatas e da Terra) - Universidade Federal de São Carlos, São Carlos, 2006. |
url |
https://repositorio.ufscar.br/handle/ufscar/4918 |
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por |
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-1 -1 |
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openAccess |
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Universidade Federal de São Carlos |
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Programa de Pós-Graduação em Física - PPGF |
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UFSCar |
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BR |
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Universidade Federal de São Carlos |
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