Carlos Alberto Dos Santos - Academia.edu (original) (raw)
Papers by Carlos Alberto Dos Santos
Revista Brasileira de História da Ciência , 2023
Físicas da URGS (CPF-URGS) foi criado em 1953 e substituído em 1959 pelo Instituto de Física. O o... more Físicas da URGS (CPF-URGS) foi criado em 1953 e substituído em 1959 pelo Instituto de Física. O objetivo deste trabalho é mostrar os elementos mais relevantes dessa efêmera existência, e como esse processo redundou em reconhecidos benefícios para o futuro do Instituto de Física, uma vez que parte significativa da cultura científica implantada no IF-UFRGS a partir dos anos 1960 tem forte conexão com as atividades desenvolvidas no CPF. Palavras-chave: história da ciência-Centro de Pesquisas Físicas-documentos primários-UFRGS.
Revista de Produtos Educacionais e Pesquisa em Ensino, 2023
Apresenta-se neste trabalho a versão 1.0 do jogo “Em busca do Prêmio Nobel” (EBPN). Trata-se de u... more Apresenta-se neste trabalho a versão 1.0 do jogo “Em busca do Prêmio Nobel” (EBPN). Trata-se de um jogo multiplataforma e multitemático, tipo tutorial com alguns elementos similares àqueles presentes em jogos RPG. Duas funcionalidades importantes foram acrescentadas à versão beta, uma de natureza administrativa e outra pedagógica. A primeira refere-se à possibilidade de o professor criar e administrar várias turmas, e a segunda refere-se à inclusão de laboratórios virtuais do portal PhET. Em ambas as versões, o conteúdo de aprendizagem é apresentado sob a forma de hipertextos e de mapas conceituais. Minibiografias das personalidades mencionadas no material didático são apresentadas como um elemento cultural. O conteúdo abordado na versão atual é a eletrodinâmica, e os textos utilizados no jogo foram elaborados de acordo com a teoria de aprendizagem de David Ausubel. Na avaliação preliminar, realizada após uma aplicação informal, os alunos corroboraram opiniões favoráveis emitidas pelos alunos que participaram da aplicação da versão beta, que abordou a atomística.
Revista Brasileira de Ensino de Física, 2024
Apresenta-se neste trabalho uma abordagem da vida científica de Ettore Majorana com o objetivo de... more Apresenta-se neste trabalho uma abordagem da vida científica de Ettore Majorana com o objetivo de fornecer subsídios para transposições didáticas durante cursos de bacharelado e licenciatura em física, bem como durante cursos de mestrado acadêmico ou profissional em ensino de física. São discutidas especialmente as contribuições de Majorana para a formulação da teoria da interação forte e para a revisão da teoria de Dirac, com o consequente surgimento do neutrino de Majorana e dos férmions de Majorana. Também são apresentados os resultados obtidos por Majorana em 1932, e que foram usados por Rabi no artigo que é considerado como a origem da ressonância magnética nuclear. Palavras-chave: Majorana, física contemporânea, neutrinos, férmions, decaimento beta. This work presents an approach to the scientific life of Ettore Majorana with the aim of providing support for didactic transpositions during undergraduate courses in physics, as well as during academic or professional master's courses in physics teaching. Specially discussed are Majorana's contributions to the formulation of the strong interaction theory and to the revision of Dirac's theory, with the consequent emergence of the Majorana neutrino and Majorana fermions. Also presented are the results obtained by Majorana in 1932, which were used by Rabi in the article that is considered the origin of nuclear magnetic resonance.
Apresenta-se aqui a resenha do livro "História da Física no Recife", recentemente publicado pela ... more Apresenta-se aqui a resenha do livro "História da Física no Recife", recentemente publicado pela Companhia Editora de Pernambuco. Ao longo dos seus sete capítulos, são apresentados os antecedentes históricos da ciência em Pernambuco; o papel de Luiz Freire no desenvolvimento da física em Pernambuco; os primórdios da criação do DF-UFPE e sua evolução desde sua criação em 1971. Palavras-chave: Física, história da física, DF-UFPE. Here is a review of the book "History of Physics in Recife", recently published by Companhia Editora de Pernambuco. Throughout its seven chapters, are presented the historical antecedents of science in Pernambuco; Luiz Freire's role in the development of physics in Pernambuco; the beginnings of the creation of DF-UFPE and its evolution since its creation in 1971.
Applied Physics Letters, 1991
Ag/Ni superlattices have been prepared by triode dc sputtering on glass substrates at 100 K. X-ra... more Ag/Ni superlattices have been prepared by triode dc sputtering on glass substrates at 100 K. X-ray diffractometry with the scattering vector perpendicular to the superlattice plane suggests structural coherence and interface sharpness whatever the thickness of the elemental layers. All the samples present (111) textures for both Ag and Ni. Magnetic measurements performed with a superconducting quantum interference device magnetometer indicate in-plane anisotropy of the magnetization and oscillatory interlayer magnetic coupling. This is confirmed by magnetoresistance measurements.
Solid State Communications, 1997
M6ssbauer spectroscopy and X-ray powder diffraction are used to show cation ordering on a natural... more M6ssbauer spectroscopy and X-ray powder diffraction are used to show cation ordering on a natural manganotantalite sample. By using electron microprobe analysis the chemical composition (Mno.aaFe0.09) (Tao.a6Nb0.14)206 has been determined. The as-received sample is partially ordered, as suggested by the low intensities of the superstructure reflections in the X-ray diffraction pattern and by the existence of two doublets in the M6ssbauer spectrum. Heat treatment in vacuum (P-10-5 Pa) at temperature T ~ 1320 K induces cation ordering as shown by the M6ssbauer spectrum, and also evidenced by the X-ray diffraction pattern.
The magnetic behaviour of the antiferromagnet FeTa 2O6 was investigated through heat capacity, ma... more The magnetic behaviour of the antiferromagnet FeTa 2O6 was investigated through heat capacity, magnetic susceptibility and magnetization measurements. The broad magnetic susceptibility curve (peaked at 15 K) presents an inflection typical of two-dimensional systems. This inflection is observed near 10 K, the temperature at which early reported M össbauer measurements indicate the onset of magnetic order. The heat capacity measurements have shown a clear transition at 8.7 K, where M össbauer measurements show complete ordering. Magnetization curves, for temperatures between 1.4 K and 5 K, display a noticeable change in slope, suggesting a spin-flop transition induced by a field higher than 10 T. It is argued that this transition, which disappears for T > 6 K, is evidence of two-dimensional behaviour.
Materials Science and Engineering: A, 1998
Samples of AISI H-12 tool steel were plasma nitrided at 500°C in a mixture of H 2-20% N 2 under a... more Samples of AISI H-12 tool steel were plasma nitrided at 500°C in a mixture of H 2-20% N 2 under a total pressure of 6 mbar, by using DC and pulsed glow discharges. The treatment time varied from 1 to 6 h. X-ray diffraction (glancing angle and q-2q geometry), conversion electron Mö ssbauer spectroscopy, conversion X-ray Mö ssbauer spectroscopy, electron probe microanalysis, optical micrograph and Vickers microhardness were used as analytical techniques. The obtained results suggest that, under the present experimental conditions: (i) The near-surface compound layer consists of a mixture of k%-Fe 4 N and m-Fe x (N, C); (ii) the near-diffusion zone compound layer consists of a mixture of k%-Fe 4 N, m-Fe x (N, C), h¦-Fe 16 N 2 and k-austenite; (iii) the dependence of compound layer thickness on nitriding time violates the parabolic behavior and emphasizes effects from cathode sputtering and radiation-enhanced diffusion.
Journal of Physics: Condensed Matter, 2007
The trirutile family of the tapiolite-like compound Fe x Ni 1−x Ta 2 O 6 was investigated by mean... more The trirutile family of the tapiolite-like compound Fe x Ni 1−x Ta 2 O 6 was investigated by means of x-ray powder diffraction (XRD) and magnetic susceptibility measurements. From Rietveld refinement it is demonstrated that the family is a homogeneous solid solution obeying Vegard's law. Magnetic susceptibility curves exhibit typical signatures of low-dimensional systems, with broadened maxima due to short range correlations immediately above the antiferromagnetic transition temperature T N. The T versus x phase diagram presents a minimum that suggests bicritical behaviour.
Journal of Physics and Chemistry of Solids, 2001
Abstract We report X-ray powder diffraction measurements performed on synthetic samples of the ta... more Abstract We report X-ray powder diffraction measurements performed on synthetic samples of the tapiolite-like Fe x Co 1− x Ta 2 O 6 solid solution. The crystal structure has been refined by the Rietveld method, by using the program fullprof . All the samples are tetragonal and were indexed to the space group P 4 2 / mnm . The end-members (FeTa 2 O 6 and CoTa 2 O 6 ) have unit-cell parameters quite similar to those previously published. The unit-cell parameters a and c for the mixed samples vary linearly with the cation substitution (Co→Fe) according to the Vegard's law in all the range of substitution.
Journal of Magnetism and Magnetic Materials, 1995
ABSTRACT We report on the observation of inverted magnetic hysteresis loops in Ag/Ni multilayers.... more ABSTRACT We report on the observation of inverted magnetic hysteresis loops in Ag/Ni multilayers. The samples were prepared by triode dc sputtering, at 100 K, with nickel layer thickness of about 8Å and Ag layer thicknesses ranging from about 5 to 40 Å. The phenomenon was observed in all the samples measured at temperatures larger than 90 K.
The European Physical Journal B, 1999
The system Cu2FeO2BO3 is an oxyborate belonging to the family of the ludwigites. In this paper we... more The system Cu2FeO2BO3 is an oxyborate belonging to the family of the ludwigites. In this paper we present AC susceptibility, magnetization measurements and Mössbauer spectroscopy on this material which allows for a complete characterization of its complex magnetic behavior. We find an hierarchy of interactions which clearly defines three regimes with decreasing temperature. These are associated with, the freezing of the Fe moments, the antiferromagnetic ordering of the Cu sub-lattice and finally the coupling between both systems.
Journal of Magnetism and Magnetic Materials, 2012
Co x Ni 1 À x Ta 2 O 6 series X-ray powder diffraction Magnetic susceptibility Broadened maximum ... more Co x Ni 1 À x Ta 2 O 6 series X-ray powder diffraction Magnetic susceptibility Broadened maximum Ion anisotropy Two dimensional AF ordering a b s t r a c t We report results on the structural and magnetic properties of the Co x Ni 1 À x Ta 2 O 6 series of compounds by X-ray powder diffraction, magnetic susceptibility and magnetization measurements. X-ray refinements carried out by the Rietveld method show that these compounds crystallize in a P4 2 /mnm tetragonal structure. Magnetic susceptibility curves show a broadened maximum witnessing that these compounds exhibit two-dimensional antiferromagnetic behaviors. All the Co x Ni 1 À x Ta 2 O 6 compounds order below 10 K and present a large ion anisotropy. The magnetic properties have been determined in both the paramagnetic and antiferromagnetic state. In the hypothesis of two dimensional AF ordering, the near neighbor exchange constants (J 1) and the next near neighbor exchange constants for two different paths (J 2 and J' 2) were determined. The composition dependence of the magnetic properties including ordering temperature, exchange constants and anisotropy factors are discussed. The drastic reduction of the ordering temperature for x ¼ 0.20 for Co x Ni 1 À x Ta 2 O 6 , suggest the hypothesis of a peculiar magnetic behavior for this composition.
Journal of Physics: Condensed Matter, 1999
Heat treatments in air and in vacuum have been performed on crystal and powder of the natural tan... more Heat treatments in air and in vacuum have been performed on crystal and powder of the natural tantalite (Mn2+0.88Fe2+0.09)(Ta5+0.86Nb5+0.14)2O2-6, as well as on powder of synthetic Fe2+(Nb5+0.6Ta5+0.4)2O6. Crystal parameters and hyperfine interactions were obtained by use of x-ray diffraction and Mössbauer spectroscopy. It is shown that the partially ordered natural sample is completely ordered after heat treatment in vacuum. Conversely,
Materials Science and Engineering, 1987
Abstract This is the third of a series of articles concerning the experimental investigation of t... more Abstract This is the third of a series of articles concerning the experimental investigation of the interdiffusion processes and solid phase reactions occurring in FeAl bilayers subjected to furnace annealing, ion beam mixing and the simultaneous combination of these two types of metallurgical treatment. In this article, we describe the characterization of the phases formed during the solid phase reaction between the two components of the bilayer under different thermal annealing conditions, by means of conversion electron Mossbauer spectroscopy and X-ray diffraction. It is demonstrated that there are two metallurgical transformations occurring in this bilayered system. The first occurs on annealing at about 600 K with the formation of the Fe2Al5 phase. The thickness of this intermetallic layer increases, consuming iron and aluminum from the original films, with increase in the temperature and time of annealing. The second takes place on annealing at and above 650 K, producing the metastable phase FeAl6, which is seen in this work to remain stable up to at least 930 K.
physica status solidi (b), 1985
Methode de calcul du deplacement quadratique moyen d'un atome de surface et donc du facteur D... more Methode de calcul du deplacement quadratique moyen d'un atome de surface et donc du facteur Debye-Waller, basee sur la theorie de la reponse lineaire
Materials Science and Engineering: A, 2003
Porous aluminum Á/bronze compacts formed from prealloyed metastable (supersolidus) powder were he... more Porous aluminum Á/bronze compacts formed from prealloyed metastable (supersolidus) powder were heated either by plasma or by a resistive furnace technique. The plasma heating was performed in two different setups: (i) Hollow Cathode Discharge (HCD) method and (ii) Shielded Cathode Discharge (SCD) method. All experiments were carried out for 12 min in hydrogen at temperatures ranging from 673 to 1323 K. In HCD, for temperatures above 773 K, a fully filled, non-porous region was obtained in the center of the compacts, exhibiting a quite different behavior than that obtained using either SCD or resistive techniques. In these cases, uniformly dispersed condensed micro-regions were detected in samples treated at temperatures higher than 1223 K. These observations are discussed in terms of the heating mechanism, mass transfer and behavior of supersolidus powder particles. A simple physical model for the creation of the central fully filled region obtained by HCD is introduced.
Journal of Physics D: Applied Physics, 1984
Discusses the relationships between the surface composition and the mechanical properties of carb... more Discusses the relationships between the surface composition and the mechanical properties of carbon steels implanted with nitrogen. Conversion electron and X-ray Mossbauer spectroscopy (CEMS and CXMS) were used to investigate the surface modifications of the implanted samples. Thermal annealing was performed in high vacuum, at temperatures between 250 and 500 degrees C, in order to simulate the temperature increase in real tribological processes. It is shown that the improved performance of nitrogen-implanted carbon steels against wear and fatigue is mainly due to the action of finely dispersed iron carbonitrides ( theta - and epsilon -Fe3(C,N)). It is shown also that the persistence of the protective action at greater depths is associated with the in-diffusion of nitrogen released by thermal decomposition of the compounds formed at the surface.
Journal of Physics D: Applied Physics, 1984
... causes hardening to depths up to 300 pm and confers both wear and fatigue resistance on engin... more ... causes hardening to depths up to 300 pm and confers both wear and fatigue resistance on engineering components (Lightfoot and Jack 1973 ... and brittle and must be removed because it spalls easily in service, leading to accelerated wear and seizure (dos Santos and Baumvol ...
Journal of Applied Physics, 1993
We present an X-band ferromagnetic resonance (FMR) study of polycrystalline single Ni films and o... more We present an X-band ferromagnetic resonance (FMR) study of polycrystalline single Ni films and of two Ni layers separated by an Ag layer at room temperature. Films were deposited by sputtering on glass using Ag over-and underlays. The single Ni films have a FMR mode with a dependence of the resonance field on the angle a between the magnetic field and the plane in good agreement with theory. In samples with two Ni films coupled through an intervenient Ag layer, only one FMR mode is observed if the two Ni have identical thicknesses. When the films have different thicknesses a second weak resonance appears. The field difference between the two modes is a measure of the coupling between the Ni films. Results were obtained for a series of ssmplcs with the ,4g thickness varying in the range 10 < t < 30 A. Surprisingly, the two modes have opposite behavior with the variation of ar, for all values of t. The results suggest that the coupling is antiferromagnetic when the field is parahel to the film plane and ferromagnetic when perpendicular, regardless of t.
Revista Brasileira de História da Ciência , 2023
Físicas da URGS (CPF-URGS) foi criado em 1953 e substituído em 1959 pelo Instituto de Física. O o... more Físicas da URGS (CPF-URGS) foi criado em 1953 e substituído em 1959 pelo Instituto de Física. O objetivo deste trabalho é mostrar os elementos mais relevantes dessa efêmera existência, e como esse processo redundou em reconhecidos benefícios para o futuro do Instituto de Física, uma vez que parte significativa da cultura científica implantada no IF-UFRGS a partir dos anos 1960 tem forte conexão com as atividades desenvolvidas no CPF. Palavras-chave: história da ciência-Centro de Pesquisas Físicas-documentos primários-UFRGS.
Revista de Produtos Educacionais e Pesquisa em Ensino, 2023
Apresenta-se neste trabalho a versão 1.0 do jogo “Em busca do Prêmio Nobel” (EBPN). Trata-se de u... more Apresenta-se neste trabalho a versão 1.0 do jogo “Em busca do Prêmio Nobel” (EBPN). Trata-se de um jogo multiplataforma e multitemático, tipo tutorial com alguns elementos similares àqueles presentes em jogos RPG. Duas funcionalidades importantes foram acrescentadas à versão beta, uma de natureza administrativa e outra pedagógica. A primeira refere-se à possibilidade de o professor criar e administrar várias turmas, e a segunda refere-se à inclusão de laboratórios virtuais do portal PhET. Em ambas as versões, o conteúdo de aprendizagem é apresentado sob a forma de hipertextos e de mapas conceituais. Minibiografias das personalidades mencionadas no material didático são apresentadas como um elemento cultural. O conteúdo abordado na versão atual é a eletrodinâmica, e os textos utilizados no jogo foram elaborados de acordo com a teoria de aprendizagem de David Ausubel. Na avaliação preliminar, realizada após uma aplicação informal, os alunos corroboraram opiniões favoráveis emitidas pelos alunos que participaram da aplicação da versão beta, que abordou a atomística.
Revista Brasileira de Ensino de Física, 2024
Apresenta-se neste trabalho uma abordagem da vida científica de Ettore Majorana com o objetivo de... more Apresenta-se neste trabalho uma abordagem da vida científica de Ettore Majorana com o objetivo de fornecer subsídios para transposições didáticas durante cursos de bacharelado e licenciatura em física, bem como durante cursos de mestrado acadêmico ou profissional em ensino de física. São discutidas especialmente as contribuições de Majorana para a formulação da teoria da interação forte e para a revisão da teoria de Dirac, com o consequente surgimento do neutrino de Majorana e dos férmions de Majorana. Também são apresentados os resultados obtidos por Majorana em 1932, e que foram usados por Rabi no artigo que é considerado como a origem da ressonância magnética nuclear. Palavras-chave: Majorana, física contemporânea, neutrinos, férmions, decaimento beta. This work presents an approach to the scientific life of Ettore Majorana with the aim of providing support for didactic transpositions during undergraduate courses in physics, as well as during academic or professional master's courses in physics teaching. Specially discussed are Majorana's contributions to the formulation of the strong interaction theory and to the revision of Dirac's theory, with the consequent emergence of the Majorana neutrino and Majorana fermions. Also presented are the results obtained by Majorana in 1932, which were used by Rabi in the article that is considered the origin of nuclear magnetic resonance.
Apresenta-se aqui a resenha do livro "História da Física no Recife", recentemente publicado pela ... more Apresenta-se aqui a resenha do livro "História da Física no Recife", recentemente publicado pela Companhia Editora de Pernambuco. Ao longo dos seus sete capítulos, são apresentados os antecedentes históricos da ciência em Pernambuco; o papel de Luiz Freire no desenvolvimento da física em Pernambuco; os primórdios da criação do DF-UFPE e sua evolução desde sua criação em 1971. Palavras-chave: Física, história da física, DF-UFPE. Here is a review of the book "History of Physics in Recife", recently published by Companhia Editora de Pernambuco. Throughout its seven chapters, are presented the historical antecedents of science in Pernambuco; Luiz Freire's role in the development of physics in Pernambuco; the beginnings of the creation of DF-UFPE and its evolution since its creation in 1971.
Applied Physics Letters, 1991
Ag/Ni superlattices have been prepared by triode dc sputtering on glass substrates at 100 K. X-ra... more Ag/Ni superlattices have been prepared by triode dc sputtering on glass substrates at 100 K. X-ray diffractometry with the scattering vector perpendicular to the superlattice plane suggests structural coherence and interface sharpness whatever the thickness of the elemental layers. All the samples present (111) textures for both Ag and Ni. Magnetic measurements performed with a superconducting quantum interference device magnetometer indicate in-plane anisotropy of the magnetization and oscillatory interlayer magnetic coupling. This is confirmed by magnetoresistance measurements.
Solid State Communications, 1997
M6ssbauer spectroscopy and X-ray powder diffraction are used to show cation ordering on a natural... more M6ssbauer spectroscopy and X-ray powder diffraction are used to show cation ordering on a natural manganotantalite sample. By using electron microprobe analysis the chemical composition (Mno.aaFe0.09) (Tao.a6Nb0.14)206 has been determined. The as-received sample is partially ordered, as suggested by the low intensities of the superstructure reflections in the X-ray diffraction pattern and by the existence of two doublets in the M6ssbauer spectrum. Heat treatment in vacuum (P-10-5 Pa) at temperature T ~ 1320 K induces cation ordering as shown by the M6ssbauer spectrum, and also evidenced by the X-ray diffraction pattern.
The magnetic behaviour of the antiferromagnet FeTa 2O6 was investigated through heat capacity, ma... more The magnetic behaviour of the antiferromagnet FeTa 2O6 was investigated through heat capacity, magnetic susceptibility and magnetization measurements. The broad magnetic susceptibility curve (peaked at 15 K) presents an inflection typical of two-dimensional systems. This inflection is observed near 10 K, the temperature at which early reported M össbauer measurements indicate the onset of magnetic order. The heat capacity measurements have shown a clear transition at 8.7 K, where M össbauer measurements show complete ordering. Magnetization curves, for temperatures between 1.4 K and 5 K, display a noticeable change in slope, suggesting a spin-flop transition induced by a field higher than 10 T. It is argued that this transition, which disappears for T > 6 K, is evidence of two-dimensional behaviour.
Materials Science and Engineering: A, 1998
Samples of AISI H-12 tool steel were plasma nitrided at 500°C in a mixture of H 2-20% N 2 under a... more Samples of AISI H-12 tool steel were plasma nitrided at 500°C in a mixture of H 2-20% N 2 under a total pressure of 6 mbar, by using DC and pulsed glow discharges. The treatment time varied from 1 to 6 h. X-ray diffraction (glancing angle and q-2q geometry), conversion electron Mö ssbauer spectroscopy, conversion X-ray Mö ssbauer spectroscopy, electron probe microanalysis, optical micrograph and Vickers microhardness were used as analytical techniques. The obtained results suggest that, under the present experimental conditions: (i) The near-surface compound layer consists of a mixture of k%-Fe 4 N and m-Fe x (N, C); (ii) the near-diffusion zone compound layer consists of a mixture of k%-Fe 4 N, m-Fe x (N, C), h¦-Fe 16 N 2 and k-austenite; (iii) the dependence of compound layer thickness on nitriding time violates the parabolic behavior and emphasizes effects from cathode sputtering and radiation-enhanced diffusion.
Journal of Physics: Condensed Matter, 2007
The trirutile family of the tapiolite-like compound Fe x Ni 1−x Ta 2 O 6 was investigated by mean... more The trirutile family of the tapiolite-like compound Fe x Ni 1−x Ta 2 O 6 was investigated by means of x-ray powder diffraction (XRD) and magnetic susceptibility measurements. From Rietveld refinement it is demonstrated that the family is a homogeneous solid solution obeying Vegard's law. Magnetic susceptibility curves exhibit typical signatures of low-dimensional systems, with broadened maxima due to short range correlations immediately above the antiferromagnetic transition temperature T N. The T versus x phase diagram presents a minimum that suggests bicritical behaviour.
Journal of Physics and Chemistry of Solids, 2001
Abstract We report X-ray powder diffraction measurements performed on synthetic samples of the ta... more Abstract We report X-ray powder diffraction measurements performed on synthetic samples of the tapiolite-like Fe x Co 1− x Ta 2 O 6 solid solution. The crystal structure has been refined by the Rietveld method, by using the program fullprof . All the samples are tetragonal and were indexed to the space group P 4 2 / mnm . The end-members (FeTa 2 O 6 and CoTa 2 O 6 ) have unit-cell parameters quite similar to those previously published. The unit-cell parameters a and c for the mixed samples vary linearly with the cation substitution (Co→Fe) according to the Vegard's law in all the range of substitution.
Journal of Magnetism and Magnetic Materials, 1995
ABSTRACT We report on the observation of inverted magnetic hysteresis loops in Ag/Ni multilayers.... more ABSTRACT We report on the observation of inverted magnetic hysteresis loops in Ag/Ni multilayers. The samples were prepared by triode dc sputtering, at 100 K, with nickel layer thickness of about 8Å and Ag layer thicknesses ranging from about 5 to 40 Å. The phenomenon was observed in all the samples measured at temperatures larger than 90 K.
The European Physical Journal B, 1999
The system Cu2FeO2BO3 is an oxyborate belonging to the family of the ludwigites. In this paper we... more The system Cu2FeO2BO3 is an oxyborate belonging to the family of the ludwigites. In this paper we present AC susceptibility, magnetization measurements and Mössbauer spectroscopy on this material which allows for a complete characterization of its complex magnetic behavior. We find an hierarchy of interactions which clearly defines three regimes with decreasing temperature. These are associated with, the freezing of the Fe moments, the antiferromagnetic ordering of the Cu sub-lattice and finally the coupling between both systems.
Journal of Magnetism and Magnetic Materials, 2012
Co x Ni 1 À x Ta 2 O 6 series X-ray powder diffraction Magnetic susceptibility Broadened maximum ... more Co x Ni 1 À x Ta 2 O 6 series X-ray powder diffraction Magnetic susceptibility Broadened maximum Ion anisotropy Two dimensional AF ordering a b s t r a c t We report results on the structural and magnetic properties of the Co x Ni 1 À x Ta 2 O 6 series of compounds by X-ray powder diffraction, magnetic susceptibility and magnetization measurements. X-ray refinements carried out by the Rietveld method show that these compounds crystallize in a P4 2 /mnm tetragonal structure. Magnetic susceptibility curves show a broadened maximum witnessing that these compounds exhibit two-dimensional antiferromagnetic behaviors. All the Co x Ni 1 À x Ta 2 O 6 compounds order below 10 K and present a large ion anisotropy. The magnetic properties have been determined in both the paramagnetic and antiferromagnetic state. In the hypothesis of two dimensional AF ordering, the near neighbor exchange constants (J 1) and the next near neighbor exchange constants for two different paths (J 2 and J' 2) were determined. The composition dependence of the magnetic properties including ordering temperature, exchange constants and anisotropy factors are discussed. The drastic reduction of the ordering temperature for x ¼ 0.20 for Co x Ni 1 À x Ta 2 O 6 , suggest the hypothesis of a peculiar magnetic behavior for this composition.
Journal of Physics: Condensed Matter, 1999
Heat treatments in air and in vacuum have been performed on crystal and powder of the natural tan... more Heat treatments in air and in vacuum have been performed on crystal and powder of the natural tantalite (Mn2+0.88Fe2+0.09)(Ta5+0.86Nb5+0.14)2O2-6, as well as on powder of synthetic Fe2+(Nb5+0.6Ta5+0.4)2O6. Crystal parameters and hyperfine interactions were obtained by use of x-ray diffraction and Mössbauer spectroscopy. It is shown that the partially ordered natural sample is completely ordered after heat treatment in vacuum. Conversely,
Materials Science and Engineering, 1987
Abstract This is the third of a series of articles concerning the experimental investigation of t... more Abstract This is the third of a series of articles concerning the experimental investigation of the interdiffusion processes and solid phase reactions occurring in FeAl bilayers subjected to furnace annealing, ion beam mixing and the simultaneous combination of these two types of metallurgical treatment. In this article, we describe the characterization of the phases formed during the solid phase reaction between the two components of the bilayer under different thermal annealing conditions, by means of conversion electron Mossbauer spectroscopy and X-ray diffraction. It is demonstrated that there are two metallurgical transformations occurring in this bilayered system. The first occurs on annealing at about 600 K with the formation of the Fe2Al5 phase. The thickness of this intermetallic layer increases, consuming iron and aluminum from the original films, with increase in the temperature and time of annealing. The second takes place on annealing at and above 650 K, producing the metastable phase FeAl6, which is seen in this work to remain stable up to at least 930 K.
physica status solidi (b), 1985
Methode de calcul du deplacement quadratique moyen d'un atome de surface et donc du facteur D... more Methode de calcul du deplacement quadratique moyen d'un atome de surface et donc du facteur Debye-Waller, basee sur la theorie de la reponse lineaire
Materials Science and Engineering: A, 2003
Porous aluminum Á/bronze compacts formed from prealloyed metastable (supersolidus) powder were he... more Porous aluminum Á/bronze compacts formed from prealloyed metastable (supersolidus) powder were heated either by plasma or by a resistive furnace technique. The plasma heating was performed in two different setups: (i) Hollow Cathode Discharge (HCD) method and (ii) Shielded Cathode Discharge (SCD) method. All experiments were carried out for 12 min in hydrogen at temperatures ranging from 673 to 1323 K. In HCD, for temperatures above 773 K, a fully filled, non-porous region was obtained in the center of the compacts, exhibiting a quite different behavior than that obtained using either SCD or resistive techniques. In these cases, uniformly dispersed condensed micro-regions were detected in samples treated at temperatures higher than 1223 K. These observations are discussed in terms of the heating mechanism, mass transfer and behavior of supersolidus powder particles. A simple physical model for the creation of the central fully filled region obtained by HCD is introduced.
Journal of Physics D: Applied Physics, 1984
Discusses the relationships between the surface composition and the mechanical properties of carb... more Discusses the relationships between the surface composition and the mechanical properties of carbon steels implanted with nitrogen. Conversion electron and X-ray Mossbauer spectroscopy (CEMS and CXMS) were used to investigate the surface modifications of the implanted samples. Thermal annealing was performed in high vacuum, at temperatures between 250 and 500 degrees C, in order to simulate the temperature increase in real tribological processes. It is shown that the improved performance of nitrogen-implanted carbon steels against wear and fatigue is mainly due to the action of finely dispersed iron carbonitrides ( theta - and epsilon -Fe3(C,N)). It is shown also that the persistence of the protective action at greater depths is associated with the in-diffusion of nitrogen released by thermal decomposition of the compounds formed at the surface.
Journal of Physics D: Applied Physics, 1984
... causes hardening to depths up to 300 pm and confers both wear and fatigue resistance on engin... more ... causes hardening to depths up to 300 pm and confers both wear and fatigue resistance on engineering components (Lightfoot and Jack 1973 ... and brittle and must be removed because it spalls easily in service, leading to accelerated wear and seizure (dos Santos and Baumvol ...
Journal of Applied Physics, 1993
We present an X-band ferromagnetic resonance (FMR) study of polycrystalline single Ni films and o... more We present an X-band ferromagnetic resonance (FMR) study of polycrystalline single Ni films and of two Ni layers separated by an Ag layer at room temperature. Films were deposited by sputtering on glass using Ag over-and underlays. The single Ni films have a FMR mode with a dependence of the resonance field on the angle a between the magnetic field and the plane in good agreement with theory. In samples with two Ni films coupled through an intervenient Ag layer, only one FMR mode is observed if the two Ni have identical thicknesses. When the films have different thicknesses a second weak resonance appears. The field difference between the two modes is a measure of the coupling between the Ni films. Results were obtained for a series of ssmplcs with the ,4g thickness varying in the range 10 < t < 30 A. Surprisingly, the two modes have opposite behavior with the variation of ar, for all values of t. The results suggest that the coupling is antiferromagnetic when the field is parahel to the film plane and ferromagnetic when perpendicular, regardless of t.