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Doctoral Thesis
DOI
10.11606/T.43.1992.tde-04122013-155549
Document
Author
Full name
Valquiria Villas Boas Gomes Missell
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1992
Supervisor
Committee
Missell, Frank Patrick (President)
Gama, Sérgio
Gomes, Affonso Augusto Guidão
Guimarães Filho, Alberto Passos
Salinas, Silvio Roberto de Azevedo
Title in Portuguese
Mecanismos de Coercividade e Fases Intergranulares em Ìmãs RFeB
Keywords in Portuguese
Física do estado sólido
Matéria condensada
Abstract in Portuguese
Estudamos os mecanismo de coercividade em ímãs sinterizados R IND. 17 Fe IND. 83-x B IND. x (R= Nd, Pr; x=8, 30) fabricados pela Sumitomo Special Metals. Co.. Medidas de campo coercivo H IND.c e do coeficiente de viscosidade magnética S IND.v foram realizadas no intervalo de temperatura de 4,2K até a temperatura de Curie T IND.c. A dependência do campo coercivo com a temperatura nestes ímãs foi analisada segundo o modelo fenomenológico de Givord e colaboradores, que considera processos de ativação térmica. A partir deste modelo foi possível avaliar os efeitos dos campos dipolares sobre a coercividade. Estes efeitos também foram avaliados através do estudo de curvas de desmagnetização obtidas em diferentes campos de saturação. A dependência angular do campo coercivo foi determinada e comparada com diversos modelos teóricos. Caracterizamos estrutural e magneticamente determinadas fases dos sistemas binário Nd-Fe e ternário Nd-Fe-B que são amostras utilizadas neste estudo foram confeccionadas no Laboratório de Materiais Magnéticos do IFUSP. Observamos uma nova fase no sistema Nd-Fe: o composto intermetálico Nd IND.5 Fe IND.17. Determinamos a estrutura cristalina, a temperatura de Curie T IND.c, a magnetização de saturação M IND.s a 4,2K e a anisotropia deste composto. Investigações modelo sobre as fases intergranulares do ímã NdFeB foram realizadas a partir do estudo de amostras do sistema Nd IND.80 Fe IND.15 B IND.5 (composição aproximada do líquido presente entre os grãos da fase magnética principal Nd IND.2 Fe IND.14 B nos ímãs NdFeB durante o processo de sinterização). Estas amostras foram tratadas termicamente a 600ºC e caracterizadas magnética e metalograficamente. A fase Nd IND.2 Fe IND.14 B foi confirmada a fase ferromagnética presente nestas amostras após o tratamento térmico. A dependência do campo coercivo com a temperatura das amostras tratadas foi estudada segundo o modelo de Givord e colaboradores e segundo o modelo de Kronmüller e colaboradores, que dá ênfase à microestrutura da amostra.
Title in English
Coercivity mechanisms and intergranular phases in RFeB magnets
Keywords in English
Condensed matter
Physics of the solid state
Abstract in English
We studied coercivity mechanisms is sintered magnets of composition R IND.17 Fe IND.83-X B IND.X (R= Nd, Pr; x= 8, 30) produced by the Sumitomo Special Metals Co.. Measurements of the coercive field H IND.C and the magnetic viscosity coefficient S IND.V were carried out in the temperature interval from 4,2K to the Curie temperature T IND.C. The temperature dependence of the coercive field in these magnets was analyzed using a phenomenological model due to Givord and co-workers which considers thermal activation processes. Using this model is was possible to evaluate the effect of dipolar fields on the coercivity. These effects were also evaluated through the study of demagnetization curves obtained in different saturating fields. The angular dependence of the coercive field was determined and compared with various theoretical models. We characterized magnetically and structurally certain phases of the binary system Nd-Fe and the ternary system Nd-Fe-B which are encountered in the intergranular regions of NdFeB permanent magnets. The samples used in this study were produced in the Magnetic Materials Laboratory of IFUSP. We observed a new phase in Nd-Fe: the intermetallic compound Nd IND.5 Fe IND.17. We determined the crystal structure, the Curie temperature T IND.C, the saturation magnetization M IND.S at 4,2K, and the anisotropy of this compound. Model investigations on the intergranular phases in NdFeB magnets were carried out on samples of compostion Nd IND.80 Fe IND.15 B IND.5 (approximate composition of the liquid present between the grains of the principal magnetic phase Nd IND.2 Fe IND.14 B in NdFeB magnets during sintering). These samples were heat treated at 600ºC and characterized magnetically and metallographically. It was confirmed that Nd IND.2 Fe IND.14 B is the ferromagnetic phase present in these samples after the heat treatment. The temperature dependence of the coercive field of the annealed samples was studied using the model of Givord et al. and that of Kronmüller et al., which emphasizes the microstructure of the sample.
 
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Publishing Date
2014-02-21
 
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