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Master's Dissertation
DOI
10.11606/D.43.1990.tde-22052013-162025
Document
Author
Full name
Vagner Bernal Barbeta
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1990
Supervisor
Committee
Becerra, Carlos Castilla (President)
Novak, Miguel
Westphal, Carlos Henrique
Title in Portuguese
Comportamento da susceptibilidade AC Xw(T,H) nos antiferromagnetos MnBR2.4H2O e Mn(Br0.7Cl0.3)2.4H2O
Keywords in Portuguese
Física do estado sólido
Matéria condensada
Abstract in Portuguese
Neste trabalho efetuamos um estudo do comportamento da susceptibilidade AC nos antiferromagnetos Mn Br IND. 2 . 4 H IND. 2 O e Mn(Br IND. 0.7 Cl IND. 0.3) IND. 2 . 4 H IND. 2 O. Fizemos medidas de susceptibilidade AC em função do campo magnético externo, para várias freqüências do campo de excitação e para temperaturas entre 1.2 e 2.5 K. Através dos dados obtidos construímos os chamados "Diagramas de Argand" para as fases antiferromagnética e paramagnética destes compostos. Os dados obtidos são comparados às previsões dadas pelo modelo de Casimir-Du Pré. Observamos que na fase paramagnética o sistema é bem descrito pelo modelo, enquanto que na fase antiferromagnética isto não ocorre. Segundo previsões devido a Fisher, a susceptibilidade em função da temperatura e a campo constante possui uma contribuição adicional da forma X ANTIND. (T,H) H POT. Y1.C IND M(T), onde CM(T) é o calor específico. O nosso estudo experimental, mostrou que o expoente Y1 = 2.36 ± 0.12, valor próximo ao previsto em modelos de Ising a 2d. Finalmente, obtivemos os expoentes críticos associados ao calor específico, = 0.107 e = 0.0538 para a amostra de Mn Br IND. 2 . 4 H IND 2 O, através das medidas de susceptibilidade AC.
Title in English
Behavior of AC Xw(T, H) susceptibility in MnBR2.4H2O and Mn (Br0.7Cl0.3) 2.4H2O antiferromagnetos
Keywords in English
Condensed matter
Solid state physics
Abstract in English
In this work we have studied the behavior of the AC susceptibility in the antiferromagnetic compound MnBr2 . 4 H2O as well as Mn(Br 0.7 Cl 0.3)2 . 4 H2O. We have measured the AC susceptibility as a function of the external magnetic field for several frequencies of the modulation field and for temperatures between 1.2 and 2.5 K. Using these data we have built the so called Argand's Diagrams" for the antiferromagnetic and paramagnetic phases. Our results are compared to the predictions of Casimir-Du Pré's model. We could observe that in the paramagnetic phase the system is well described by the model, while in the antiferromagnetic phase this is not true. According to Fisher's predictions, the temperature dependence of the susceptibility at constant magnetic field, has an additional contribution of the form '(T,H) HY1.CM(T), where CM(T) is the specific heat. Our experimental study has demonstrated that the exponent Y1 = 2.36 ± 0.12, which is around the value predicted for a Ising's 2d model. Finally, we have obtained the critical exponents associated with the specific heat, = 0.107 and = 0.0538, for the sample of MnBr2 . 4 H2O, through measurements of AC susceptibility.
 
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Publishing Date
2013-05-23
 
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