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Previous issue date: 2012-03-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this experimental study sintetic samples of Jacobsites (MnFe2O4) were synthesized
by the Pechini method and calcined within ambient atmosphere and afterwards in the
vacuum from 400 to 700?C, the range of calcination temperatures. The X-Ray Diffraction
(XRD) and the Scanning Electronic Microscopy (SEM) analysis have shown that the samples
treated at 400?C temperature are composed by a simple type of spinel phase, with a
crystallite size of 8:8nm for the sample calcined in ambient atmosphere and 20; 1nm for the
sample treated in the vacuum, showing that the cristallite average size can be manipulated
by the atmosphere control. The hysteresis loops for the sample calcined at 400?C in ambient
atmosphere reveal features of superparamagnetic behavior with magnetization 29:3emu=g at
the maximum field of 1:2T. The sample calcined in 400oC under vacuum show magnetization
= 67emu=g at the maximum field of 1:5T. The sample treated at 500oC, under ambient
atmosphere, has shown besides the spinel phase, secondary phases of hematite (Fe2O3) and
bixbyite (FeMnO3). The hysteresis loops demonstrate a sharp drop of the magnetization
compared to the previous sample. The analysis has revealed that for the samples treated in
higher temperatures (600?C and 700?C) its observed the absence of the spinel phase and the
maintenance of the bixbyite and hematite. The hysteresis loops for those samples in accordance
to the external magnetic field are straight lines crossing the origin, consistent with the
antiferromagnetic behavior of the phases.The M?ssbauer espectroscopy show to the sample
calcined at 400?C within ambiente atmosphere two sextet and one doublet. The two sextets
are assigned to the hyperfine fields related to the magnetic deployment in the nuclei of Fe3+
ions, at the tetraedric and octaedric sites. The doublet is assigned to superparamagnetic
behavior of the particles with smaller diameter than dc . Now the sample calcined at 400?C
under vacuum only show two sextet / ?Neste estudo experimental, amostras sint?ticas de Jacobsitas (MnF e2O4) foram sintetizadas pelo m?todo Pechini e calcinadas em atmosfera ambiente e em v?cuo de 400 at? 700?C. An?lises de difra??o de raio-x (DRX) e microscopia eletr?nica de varredura (MEV)
revelaram que a amostra calcinada em 400?C ? composta por uma fase simples tipo espin?lio, com tamanho m?dio do cristalito de 8,8nm para amostra calcinada em atmosfera ambiente, e 20,1nm para amostra calcinada em v?cuo, indicando que o tamanho m?dio do cristalito
pode ser manipulado pelo controle da atmosfera. A curva de magnetiza??o para amostra calcinada a 400?C em atmosfera ambiente revela caracter?sticas de comportamento superparamagn?tico, com magnetiza??o de 29:3emu=g num campo m?ximo de 1.2T . J? a amostra
calcinada em 400?C sob v?cuo apresentou magnetiza??o = 67emu/g no campo m?ximo de 1.5T . A amostra tratada em 500 ]C, em atmosfera ambiente, acusa al?m da fase espin?lio, fases secund?rias de hematita (Fe2O3) e bixbyita (FeMnO3). A curva de magnetiza??o mostra uma queda abrupta na magnetiza??o comparada com as amostras anteriores. A an?lise mostra que, para mais altas temperaturas (600?C and 700?C), observou-se apenas a continua??o das fases hematita e bixbyita. A curva de magnetiza??o dessas amostras s?o linhas
retas cortando a origem, consistente com o comportamento antiferromagn?tico dessas fases.
A espectroscopia M?ssbauer revelou que para a amostra calcinada em 400?C em atmosfera
ambiente h? dois sextetos e um dubleto. Os dois sextetos s?o atribu?dos aos campos hiperfinos referentes ao desdobramento magn?tico no n?cleo dos ?ons Fe3+, nos s?tios tetra?dricos
e octa?dricos. O dubleto ? atribu?do ao comportamento superparamagn?tico das part?culas
com di?metro menor que dc. J? a amostra calcinada em 400?C sob v?cuo apresenta apenas
dois sextetos.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/18600 |
| Date | 27 March 2012 |
| Creators | Barbosa, Mateus Bruno |
| Contributors | CPF:24150720444, http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4785558U2, Carri?o, Artur da Silva, CPF:33014419704, http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4787041Z8, Soares, Jo?o Maria, CPF:67136958415, http://lattes.cnpq.br/2108722656012583, Ara?jo, Jos? Humberto de |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em F?sica, UFRN, BR, F?sica da Mat?ria Condensada; Astrof?sica e Cosmologia; F?sica da Ionosfera |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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