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Previous issue date: 2010-09-10 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Samples of lanthanum Ortoferrites doped with strontium were synthesized in a single
phase by the sol-gel method. Two samples were prepared, one by varying the concentration of
strontium in lanthanum ortoferrites La1?xSrxFeO3?? with (0 ? x ? 0.5), and another batch
of samples of type, La1/3Sr2/3FeO3??, now varying only the temperature of calcination. Our
samples were obtained by Pechini method and sintered in air and oxygen atmospheric. Their
crystal structures were determined by x-ray diraction (XRD), scanning electron microscopy
(SEM), where we observed that the samples (0 ? x ? 0.3) have orthorhombic symmetry and
the volume of the single cell decreases with the increasing of concentration of strontium. For
x = 0.5 it is only observed the simple phase when that is sintered in O2 atmospheric. Their
magnetic characteristics were obtained by the M?ssbauer spectroscopy and magnetic measurements.
The magnetization measurements for samples La1?xSrxFeO3?? with (0 ? x ? 0.5)
revealed that the magnetization decreases with increasing concentration of strontium, but
for the sample x = 0.4 the magnetization shows a high coercive field and a ferrimagnetic
behavior, which is attributed to a small amount of strontium hexaferrite. As for the samples
La1/3Sr2/3FeO3?? calcined between 800 oC e 1200 oC. The hysteresis curves revealed
two distinct behaviors: an declined antiferromagnetic behavior (Canted) for samples calcined
between 800 oC and 1000 oC and a paramagnetic behavior for the samples calcined at
1100 oC e 1200 o C. Thermal hysteresis and sharp peaks around the N?el temperature (TN),
over the curves of specific heat as a function of temperature was only observed in calcined
samples with 1100 oC and 1200 oC. This eect is attributed to the charge ordering. These
results indicate that the charge ordering occurs only in the samples without oxygen deficiency.
Magnetic measurements as a function of temperature are also in agreement with this
interpretation / ?Amostras de ortoferritas de lant?nio dopados com estr?ncio foram sintetizados na
forma de fase simples pelo m?todo Sol-Gel. Dois lotes de amostras foram preparadas, um
variando a concentra??o do estr?ncio nas ortoferritas de lant?nio La1?xSrxFeO3?? com
(0 ? x ? 0.5), e um outro lote de amostras do tipo La1/3Sr2/3FeO3??, agora variando
somente a temperatura de calcina??o. Nossas amostras foram obtidas pelo m?todo Pechini, e
sinterizados em atmosfera de oxig?nio. Suas estruturas cristalinas foram determinadas por difratometria
de raios -x (DRX), microscopia eletr?nica de varredura (MEV), onde observamos
que as amostras (0 ? x ? 0.3) possuem simetria ortorr?mbica, e o volume da c?lula unit?ria
diminui com o aumento da concentra??o de estr?ncio. Para x=0.5 somente ? observada fase
simples quando esta ? sinterizada na atmosfera de O2. Suas caracter?sticas magn?ticas foram
obtidas por meio de espectroscopia M?ossbauer e medidas de magnetiza??o. As medidas de
magnetiza??o para as amostras La1?xSrxFeO3?? com (0 ? x ? 0.5) revelaram que a magnetiza
??o decresce com o aumento da concentra??o de estr?ncio, contudo para a amostra x=0.4
a magnetiza??o mostra um alto campo coercivo e um comportamento ferrimagn?tico, o qual
? atribuido a uma pequana quantidade de Hexaferrita de estr?ncio. J? para as amostras
La1/3Sr2/3FeO3??, calcinadas entre 800 oC e 1200 oC , as curvas de histerese revelaram dois
comportamentos distintos: Um comportamento antiferromagn?tico declinado (Canted) para
as amostras calcinadas entre 800 oC e 1000 oC e um comportamento paramagn?tico para as
amostras calcinadas em 1100 oC e 1200 o C. Histereses t?rmicas e picos acentuados em torno
da temperatura de N?el (TN), sobre as curvas de calor espec? co em fun??o da temperatura
foi observada apenas nas amostras calcinadas com 1100 oC e 1200 oC . Este efeito ? atribuido
ao ordenameto de carga. Estes resultados indicam que o ordenamento de carga ocorre
somente nas amostras sem de ci?ncia de oxig?nio. Medidas de Magnetiza??o em fun??o da
temperatura tamb?m est?o de acordo com esta interpreta??o.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/18603 |
| Date | 10 September 2010 |
| Creators | Silva, Rodolfo Bezerra da |
| Contributors | CPF:24150720444, http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4785558U2, Medeiros, Suzana N?brega de, CPF:78609801420, http://lattes.cnpq.br/2148858591663240, Xavier J?nior, Milton Morais, CPF:44366116472, http://lattes.cnpq.br/3128669965557866, 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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