Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / This study describes two families of transition metal oxides (OMT). Because of its potential
and diversity of physical properties, the OMT are promising candidates for technological applications.
In contrast, physically understand the complex relationship of these properties has been
the main challenge of the research in this area. One of the families that was studied in this work
are composed of Ruddlesden Popper type (RP), nickel base, of formula Lan+1NinO3n+1. The RP
oxides have become more popular in the decade of 80, when it was discovered that a compound
of this family, the La2CuO4− can become superconductive when appropriately doped. Another
important property associated with the RP oxides is the colossal magnetoresistance, observed
in the manganese-based compounds, such as Ca3−xLaxMn2O7. Another family of OMT studied
in this work are the compounds garnets type of formula R3Fe5O12 (Where R is rare earth element
or Y). This family is known to be rich in physical properties, especially magnetic, The
magnetism of these compounds is associated mainly with the ferrimagnetic interaction between
ions of Fe3+ in octahedral and tetrahedral coordination. The magnetic moment resulting from
interactions of the Fe3+ can orient yourself antiferromagnetic with the network ion R, if it is a
rare earth magnetic. A property that has been strongly investigated in compounds garnets is the
magnetocaloric effect (EMC). This effect, which tracks the magnetic transitions, is more relevant
and meaningful in compounds that are promising candidates for use in magnetic refrigeration.
To investigate some of the physical properties of these systems were synthesized compounds
(Dy, Y)3Fe3Al2O12 and Lan+1(Ni1−xZnx)nO3n+1 (n = 1, 2, 3 e 0 ≤ x ≤ 0.5). To synthesize the
samples used two methods, combustion reaction (RC) and coprecipitation (CP). Both methods
have proven effective for obtaining samples with the desired phase. The technique of X-ray
diffraction, together with the Rieteveld refinement method was used to extract crystallographic
information of the synthesized compounds. Morphological information of samples, such as size,
shape and distribution of particles were investigated by the technique of scanning electron microscopy.
The micrographs show that regardless of the synthesis method, the particle shape
is not well defined and the size distribution is inhomogeneous. Some samples of garnets type,
synthesized by CP, have particle size in the nanoscale. Some compounds were characterized by
electrical resistivity measurements as a function of temperature, where it was found that the
series La2Ni1−xZnxO4 it has semiconducting properties in the temperature range from 10 KM to
300 K. The magnetic properties were investigated by magnetization measurements as a function
of temperature and magnetic field, where it was found that the magnetism of both systems is
affected by the inclusion of non-magnetic ions. EMC was investigated in two samples of garnets
type, the data were obtained from the magnetization as a function of temperature and it
was found that the aluminum insert in the structure, replacing the iron, decreased temperature
magnetic transition, but also reduced the intensity EMC. / Neste trabalho estudamos duas fam´ılias de ´oxidos de metais de transi¸c˜ao (OMT). Devido
ao seu potencial e diversidade de propriedades f´ısicas, os OMT s˜ao promissores candidatos a
aplica¸c˜oes tecnol´ogicas. Em contrapartida, compreender fisicamente a complexa rela¸c˜ao destas
propriedades tem sido o principal desafio das pesquisas desta ´area.Uma das fam´ılias que estudamos
neste trabalho s˜ao compostos do tipo Ruddlesden Popper (RP) a base de n´ıquel, com
f´ormula Lan+1NinO3n+1. Os ´oxidos RP tornaram-se mais conhecidos na d´ecada de 80, quando
foi descoberto que um composto desta fam´ılia, o La2CuO4− , pode se tornar supercondutor
quando apropriadamente dopado. Outra importante propriedade associada com os ´oxidos RP
´e a magnetorresistˆencia colossal, observada em compostos a base de manganˆes, a exemplo do
Ca3−xLaxMn2O7. Outra fam´ılia de OMT estudada neste trabalho s˜ao compostos tipo garnets
de f´ormula R3Fe5O12 (onde R ´e um elemento terra rara ou Y). Essa fam´ılia ´e conhecida por
sua riqueza de propriedades f´ısicas, especialmente magn´eticas. O magnetismo destes compostos
est´a associado, principalmente, com a intera¸c˜ao ferrimagn´etica entre os ´ıons de Fe3+ em coordena
¸c˜ao octa´edrica e tetra´edrica. O momento magn´etico resultante das intera¸c˜oes do Fe3+ pode
se orientar antiferromagneticamente com a rede do ´ıon R, se ele for um terra rara magn´etico.
Uma propriedade que vem sendo investigada nos compostos garnets ´e o efeito magnetocal´orico
(EMC). Este efeito, que acompanha as transi¸c˜oes magn´eticas, ´e mais relevante e significativo
em compostos que s˜ao promissores candidatos a aplica¸c˜ao em refrigera¸c˜ao magn´etica. Para
investigar algumas das propriedades f´ısicas destes sistemas, foram sintetizados compostos (Dy,
Y)3Fe3Al2O12 e Lan+1(Ni1−xZnx)nO3n+1 (n = 1, 2, 3 e 0 ≤ x ≤ 0.5). Para a s´ıntese das
amostras foram utilizados dois m´etodos, rea¸c˜ao de combust˜ao (RC) e coprecipita¸c˜ao (CP). A
t´ecnica de difra¸c˜ao de raios X, aliada ao m´etodo de refinamento Rieteveld, foi utilizada para extrair
informa¸c˜oes cristalogr´aficas dos compostos sintetizados. Informa¸c˜oes sobre morfologia das
amostras, como tamanho, forma e distribui¸c˜ao das part´ıculas, foram investigadas pela t´ecnica
de microscopia eletrˆonica de varredura. As micrografias revelam que independentemente do
m´etodo de s´ıntese a forma das part´ıculas n˜ao ´e bem definida e a distribui¸c˜ao de tamanhos n˜ao ´e
homogˆenea. Algumas amostras do tipo garnets, sintetizadas por CP, tˆem part´ıculas de tamanho
na escala nanom´etrica. Alguns compostos foram caracterizados por medidas de resistividade
el´etrica em fun¸c˜ao da temperatura, em que se verificou que a s´erie La2Ni1−xZnxO4 tem propriedades
semicondutoras no intervalo t´ermico de 10 K a 300 K. As propriedades magn´eticas foram
investigadas por medidas de magnetiza¸c˜ao em fun¸c˜ao da temperatura e do campo magn´etico,
em que se verificou que o magnetismo de ambos os sistemas ´e afetado pela inser¸c˜ao dos ´ıons
n˜ao magn´eticos. O EMC foi investigado em duas amostras do tipo garnets, os dados foram
obtidos das medidas de magnetiza¸c˜ao em fun¸c˜ao da temperatura e se verificou que a inser¸c˜ao
do alum´ınio na estrutura, em substitui¸c˜ao ao ferro, causou uma diminui¸c˜ao na temperatura de
transi¸c˜ao magn´etica, por´em tamb´em reduziu a intensidade do EMC.
| Identifer | oai:union.ndltd.org:IBICT/oai:ri.ufs.br:riufs/5254 |
| Date | 25 May 2016 |
| Creators | Silva, Cláudia Adriana da |
| Contributors | Salazar, Nelson Orlando Moreno |
| Publisher | Universidade Federal de Sergipe, Pós-Graduação em Física, UFS, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFS, instname:Universidade Federal de Sergipe, instacron:UFS |
| Rights | info:eu-repo/semantics/openAccess |
Page generated in 0.003 seconds