Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work, monocrystalline samples of the system TRNi3Ga9 (TR = Gd Tb, Dy, Ho,
Er, Lu) were synthesized by the metal flux technique. The physical properties were studied
by X-ray diffraction, magnetic susceptibility, function field magnetization, electrical
resistivity and specific heat. This family of compounds crystallizes into a trigonal structure
of type ErNi3Al9 with spatial group 32. The LuNi3Ga9, non-magnetic isostructural
sample was used to subtract lattice and electronic contributions to the Cp for the other
rare earths. In the samples grown with TR = Gd, Tb, Dy, Ho, Er show antiferromagnetic
ordering with TN < 20 K. Except for the sample GdNi3Ga9 an anisotropic behavior
was observed in the curves of (T) e M(H) as a function of the direction of application
of the magnetic field Which we associate with effects of crystalline electric field (CEF).
Furthermore, both the TN and the term CW do not stagger with the term of de Gennes
indicating that the CEF effects and the anisotropic character of the exchange interaction
are present in this family of compounds.
In order to analyze the evolution of the magnetic properties along this series of compounds
we use a mean field model including anisotropic exchange interactions, crystalline
electric field effects and quadrupole interactions. The measures of (T), M(H) and of
the specific heat were simulated for emph TR = Tb, Dy, Ho and Er making it possible
to extract the exchange parameters (J′s), the terms of CEC (B′s) and the quadrupolar
terms (K′s). In addition, from this data set is constructed the levels scheme of the crystalline
electric field with its respective wave functions. The analysis of the data extracted
from the simulation allows us to understand the change in orientation of the axis of easy
magnetization throughout the series. To TR = Tb, Dy easy magnetization axis is located
along the ab plane, whereas for the TR = Er, the easy magnetization axis is oriented in
the direction c. This behavior is consistent with the signal change in the CEF B0
2 term
which was negative for ErNi3Ga9 and positive for the other rare earths. In addition, the
total division of the multiplet of the CEF scheme of levels decreases with the increase of
the atomic number (Tb - Er) of the rare earth ion in the same way as the dominant term
of the CEF Hamiltonian, B0
2 . We have tried to associate this fact with the systematic
change in the c/a ratio that increases from Tb to Er. / Neste trabalho, foram sintetizadas amostras monocristalinas do sistema TRNi3Ga9 (TR
= Gd Tb, Dy, Ho, Er, Lu) atrav´es da t´ecnica de fluxo met´alico. As propriedades f´ısicas
foram estudadas atrav´es de difra¸c˜ao de raios X, susceptibilidade magn´etica, magnetiza¸c˜ao
em fun¸c˜ao do campo, resistividade el´etrica e calor espec´ıfico. Esta fam´ılia de compostos
cristaliza em uma estrutura trigonal do tipo ErNi3Al9 com grupo espacial R32. A amostra
LuNi3Ga9, isoestrutural n˜ao magn´etico, foi utilizada para subtrair as contribui¸c˜oes da
rede e eletrˆonica ao Cp para os demais terras raras. Nas amostras crescidas com TR
= Gd, Tb, Dy, Ho, Er apresentaram ordenamento antiferromagn´etico com TN < 20 K.
Com exce¸c˜ao da amostra GdNi3Ga9 um comportamento anisotr´opico foi observado nas
curvas de (T) e M(H) em fun¸c˜ao da dire¸c˜ao de aplica¸c˜ao do campo magn´etico a qual
associamos a efeitos de campo el´etrico cristalino (CEC). Al´em disso, tanto a TN quanto o
termo CW n˜ao escalonam com o termo de de Gennes indicando que os efeitos de CEC e
o car´ater anisotr´opico da intera¸c˜ao de troca est˜ao presentes nessa fam´ılia de compostos.
Com o intuito de analisar a evolu¸c˜ao das propriedades magn´eticas ao longo dessa
s´erie de compostos n´os utilizamos um modelo de campo m´edio incluindo intera¸c˜oes de
troca anisotr´opica, efeitos de campo el´etrico cristalino e intera¸c˜oes quadrupolares. As
medidas de (T), M(H) e do calor esp´ecifico foram simuladas para TR = Tb, Dy, Ho e
Er possibilitando a extra¸c˜ao dos parˆametros de troca (J′s), os termos de CEC (B′s) e os
termos quadrupolares (K′s). Al´em disso, a partir desse conjunto de dados ´e constru´ıdo o
esquema de n´ıveis do campo el´etrico cristalino com suas respectivas fun¸c˜oes de ondas. A
an´alise dos dados extra´ıdos da simula¸c˜ao nos permite entender a mudan¸ca da orienta¸c˜ao
do eixo de f´acil magn´etiza¸c˜ao ao longo da s´erie. Para TR = Tb, Dy, Ho o eixo de f´acil
magnetiza¸c˜ao est´a situado ao longo do plano ab enquanto que para o TR = Er o eixo de
f´acil magnetiza¸c˜ao estar orientado na dire¸c˜ao c. Esse comportamento ´e consistente com a
mudan¸ca de sinal no termo de CEC B0
2 o qual foi negativo para ErNi3Ga9 e positivo para
os demais terras raras. Al´em disso, a divis˜ao total do multipleto do esquema de n´ıveis do
CEF decresce com o aumento do numero atˆomico (Tb - Er) do ´ıon terra rara da mesma
forma que o termo dominante da hamiltoniana de CEC, B0
2 . N´os tentamos associar esse
fato com a sistem´atica mudan¸ca na raz˜ao c/a que aumenta de Tb para Er.
| Identifer | oai:union.ndltd.org:IBICT/oai:ri.ufs.br:riufs/5253 |
| Date | 20 March 2017 |
| Creators | Silva, Leonardo de Sousa |
| Contributors | Duque, José Gerivaldo dos Santos |
| 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 |
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