O presente trabalho propôs investigar a obtenção e caracterização de fases de compostos ternários... more O presente trabalho propôs investigar a obtenção e caracterização de fases de compostos ternários FeCuAl. As amostras foram obtidas a partir de elementos de alta pureza (99,5%), fundidos conjuntamente em um forno arco voltaico, sob uma atmosfera de argônio, e posteriormente tratadas a uma temperatura de 1000°C, seguido de resfriamento rápido. Para determinação das estruturas e das fases, realizaram-se medidas de difração de raio-x (DRX) e analisaram-se os espectros através do método de Rietveld com o auxilio do software WinPlotR (FullProf). Obteve-se uma fase majoritária de estrutura cúbica de corpo centrado (bcc), e uma das amostras apresentou a formação de um composto Al2Cu. Os parâmetros de rede das amostras, revelam que a inclusão dos átomos de Cu e Al na estrutura do Fe (2.87 Å) expande um pouco a sua rede para 2.8829Å. Determinou-se a composição das fases, obtendo-se a fase I, que supõe-se ser uma solução sólida, com 100% para as amostras F22 e F24, e a amostra F23 apresentou 93.66% da fase I e 6.34% da fase II (composto Al2Cu).
The electronic structure and magnetic properties of Fe4C are investigated with the first-principl... more The electronic structure and magnetic properties of Fe4C are investigated with the first-principles discrete variational method (DV) in spin-polarized case. It is used for the local spin density approximation of the density functional theory. Clusters of 21 and 27 atoms were adopted to represent the two non-equivalent iron sites in this compound. The calculated magnetic moments for the corner and face centered iron sites are 2.63\muB and 1.77\muB, respectively, which are in very good agreement with the experimental results. A collapse of the magnetic moment for both inequivalent iron sites was verified above 12% of contraction of the lattice spacing. The C atom acts as an acceptor for electrons in this host.
The first-principles molecular cluster discrete variational method (DV) is used to investigate th... more The first-principles molecular cluster discrete variational method (DV) is used to investigate the electronic structure and local magnetic properties of Cr impurities in bcc iron and Fe/Cr interfaces. The spin polarized case is considered within the framework of the local-spin-density approximation of the density function theory. The effect on the local moment and hyperfine magnetic field (Fermi contact term) of adding Cr atoms in the vicinity of Fe atoms is investigated. For a Cr impurity in bcc iron the calculated magnetic moment and hyperfine field is -0.62 µB and -300 kG, respectively. For pure chromium we obtained -0.49 µB and -67 kG. The Fe moment is sensitive to the separation between Cr atoms in the first shell of neighbors.
Co2+x+yMn1-xAl1-y intermetallic compounds have been prepared by arc melting and studied with X-ra... more Co2+x+yMn1-xAl1-y intermetallic compounds have been prepared by arc melting and studied with X-ray diffraction and magnetization measurements to ascertain the effect of deviations of composition from the stoichiometry on the ferromagnetism of this system. Hysteresis loops registered at room temperature show a soft ferromagnetic behavior in excess Co. In off-stoichiometric alloys the saturation magnetization is lower than in Co2MnAl, whereas the Curie temperature TC is higher in all the studied alloys. TC varies substantially with variations in composition and increases with the Mn content. In the source of this behavior a volume effect is inferred which is expected to lead to strengthened ferromagnetic exchanges.
The electronic structure and magnetic properties of the Fe/N/Fe multi-layers were obtained by mea... more The electronic structure and magnetic properties of the Fe/N/Fe multi-layers were obtained by means of self-consistent band structure calculations employing the Linear Muffin-Tin Orbital method (LMTO). Calculations were carried out for several lattice parameters in order to obtain ground-state properties such as equilibrium lattice parameters and the critical pressure of these multi-layers. The analysis of the density of states at equilibrium volume gives a good understanding of the electronic and magnetic properties of these multi-layers, showing remarkable differences from the bulk properties of iron-based nitrides. Ferromagnetic calculations show that the Fe/N/Fe multi-layers, at equilibrium volume, have a ferrimagnetic order of 1.45 μB and −0.22 μB as the magnetic moments at the two non-equivalent iron sites. At nitrogen sites a moment magnetic of −0.16 μB was found, which is opposite to the very small values found in bulk iron nitrides. The magnetic moment and hyperfine field (the Fermi Contact) show a strong dependence with the lattice spacing with a collapse of the magnetic moments at certain critical lattice spacing.
Autor para correspondência: DCET -URI, Prédio 7, Universidade Regional Integrada do Alto Uruguai ... more Autor para correspondência: DCET -URI, Prédio 7, Universidade Regional Integrada do Alto Uruguai e Missões, Av. Universidade das Missões, 464 -Santo Ângelo/RS, CEP: 9802-470
In this study we report results of X-ray diffraction and dc magnetization measurements in Mn1−xAl... more In this study we report results of X-ray diffraction and dc magnetization measurements in Mn1−xAl1−yCux+y alloys in the κ phase which has a B2 (CsCl-type) structure. Increasing Cu doping not only weakens the ferromagnetic order and strongly affects Curie temperature (TC) but also imposes a competition mechanism between ferromagnetic and ferrimagnetic spin correlations which induces the appearance of cluster spin-glasslike phase at low temperatures.
O presente trabalho propôs investigar a obtenção e caracterização de fases de compostos ternários... more O presente trabalho propôs investigar a obtenção e caracterização de fases de compostos ternários FeCuAl. As amostras foram obtidas a partir de elementos de alta pureza (99,5%), fundidos conjuntamente em um forno arco voltaico, sob uma atmosfera de argônio, e posteriormente tratadas a uma temperatura de 1000°C, seguido de resfriamento rápido. Para determinação das estruturas e das fases, realizaram-se medidas de difração de raio-x (DRX) e analisaram-se os espectros através do método de Rietveld com o auxilio do software WinPlotR (FullProf). Obteve-se uma fase majoritária de estrutura cúbica de corpo centrado (bcc), e uma das amostras apresentou a formação de um composto Al2Cu. Os parâmetros de rede das amostras, revelam que a inclusão dos átomos de Cu e Al na estrutura do Fe (2.87 Å) expande um pouco a sua rede para 2.8829Å. Determinou-se a composição das fases, obtendo-se a fase I, que supõe-se ser uma solução sólida, com 100% para as amostras F22 e F24, e a amostra F23 apresentou 93.66% da fase I e 6.34% da fase II (composto Al2Cu).
The electronic structure and magnetic properties of Fe4C are investigated with the first-principl... more The electronic structure and magnetic properties of Fe4C are investigated with the first-principles discrete variational method (DV) in spin-polarized case. It is used for the local spin density approximation of the density functional theory. Clusters of 21 and 27 atoms were adopted to represent the two non-equivalent iron sites in this compound. The calculated magnetic moments for the corner and face centered iron sites are 2.63\muB and 1.77\muB, respectively, which are in very good agreement with the experimental results. A collapse of the magnetic moment for both inequivalent iron sites was verified above 12% of contraction of the lattice spacing. The C atom acts as an acceptor for electrons in this host.
The first-principles molecular cluster discrete variational method (DV) is used to investigate th... more The first-principles molecular cluster discrete variational method (DV) is used to investigate the electronic structure and local magnetic properties of Cr impurities in bcc iron and Fe/Cr interfaces. The spin polarized case is considered within the framework of the local-spin-density approximation of the density function theory. The effect on the local moment and hyperfine magnetic field (Fermi contact term) of adding Cr atoms in the vicinity of Fe atoms is investigated. For a Cr impurity in bcc iron the calculated magnetic moment and hyperfine field is -0.62 µB and -300 kG, respectively. For pure chromium we obtained -0.49 µB and -67 kG. The Fe moment is sensitive to the separation between Cr atoms in the first shell of neighbors.
Co2+x+yMn1-xAl1-y intermetallic compounds have been prepared by arc melting and studied with X-ra... more Co2+x+yMn1-xAl1-y intermetallic compounds have been prepared by arc melting and studied with X-ray diffraction and magnetization measurements to ascertain the effect of deviations of composition from the stoichiometry on the ferromagnetism of this system. Hysteresis loops registered at room temperature show a soft ferromagnetic behavior in excess Co. In off-stoichiometric alloys the saturation magnetization is lower than in Co2MnAl, whereas the Curie temperature TC is higher in all the studied alloys. TC varies substantially with variations in composition and increases with the Mn content. In the source of this behavior a volume effect is inferred which is expected to lead to strengthened ferromagnetic exchanges.
The electronic structure and magnetic properties of the Fe/N/Fe multi-layers were obtained by mea... more The electronic structure and magnetic properties of the Fe/N/Fe multi-layers were obtained by means of self-consistent band structure calculations employing the Linear Muffin-Tin Orbital method (LMTO). Calculations were carried out for several lattice parameters in order to obtain ground-state properties such as equilibrium lattice parameters and the critical pressure of these multi-layers. The analysis of the density of states at equilibrium volume gives a good understanding of the electronic and magnetic properties of these multi-layers, showing remarkable differences from the bulk properties of iron-based nitrides. Ferromagnetic calculations show that the Fe/N/Fe multi-layers, at equilibrium volume, have a ferrimagnetic order of 1.45 μB and −0.22 μB as the magnetic moments at the two non-equivalent iron sites. At nitrogen sites a moment magnetic of −0.16 μB was found, which is opposite to the very small values found in bulk iron nitrides. The magnetic moment and hyperfine field (the Fermi Contact) show a strong dependence with the lattice spacing with a collapse of the magnetic moments at certain critical lattice spacing.
Autor para correspondência: DCET -URI, Prédio 7, Universidade Regional Integrada do Alto Uruguai ... more Autor para correspondência: DCET -URI, Prédio 7, Universidade Regional Integrada do Alto Uruguai e Missões, Av. Universidade das Missões, 464 -Santo Ângelo/RS, CEP: 9802-470
In this study we report results of X-ray diffraction and dc magnetization measurements in Mn1−xAl... more In this study we report results of X-ray diffraction and dc magnetization measurements in Mn1−xAl1−yCux+y alloys in the κ phase which has a B2 (CsCl-type) structure. Increasing Cu doping not only weakens the ferromagnetic order and strongly affects Curie temperature (TC) but also imposes a competition mechanism between ferromagnetic and ferrimagnetic spin correlations which induces the appearance of cluster spin-glasslike phase at low temperatures.
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Papers by J C Krause