Navegação Produção Científica por Autor "Gusmao, Miguel Angelo Cavalheiro"
Resultados 21-35 de 35
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Magnetic behavior of the NixFe1−xNb2O6 quasi-one-dimensional system : isolation of Ising chains by frustration
Sarvezuk, Paulo Willian Carvalho; Gusmao, Miguel Angelo Cavalheiro; Cunha, Joao Batista Marimon da; Isnard, Olivier (2012) [Artigo de periódico]Physical properties of the NixFe1−xNb2O6 compounds are investigated combining x-ray and neutron powder diffraction with magnetic and calorimetry measurements as well as 57Fe Mössbauer spectroscopy. This system is known to ... -
Magnetic susceptibility and specific heat of the anderson lattice : perturbative expansion around the atomic limit
Brunnet, Leonardo Gregory; Gusmao, Miguel Angelo Cavalheiro; Iglesias, Jose Roberto (1992) [Artigo de periódico]The Green's functions relevant to the periodic Anderson Hamiltonian are calculated via perturbation theory around the atomic limit. The approximation reproduces exact results in three different limits: zero bandwidth, zero ... -
Nature of insulating state in the three-band hubbard model : a tight-binding approach
Beatrici, Anderson; Gusmao, Miguel Angelo Cavalheiro (1995) [Artigo de periódico]We study the three-band Hubbard model, commonly used to describe the copper-oxygen planes of high-Tc superconductors, from the point of view of electronic properties. Utilizing perturbation theory around the atomic limit ... -
New investigation of the magnetic structure of CoNb2O6 columbite
Sarvezuk, Paulo Willian Carvalho; Kinast, Eder Julio; Colin, C. V.; Gusmao, Miguel Angelo Cavalheiro; Cunha, Joao Batista Marimon da; Isnard, Olivier (2011) [Trabalho completo publicado em evento] -
Phase transitions in asymmetric potts models : breakdown of classical mean-field picture
Gusmao, Miguel Angelo Cavalheiro (1987) [Artigo de periódico]It is shown that mean-field theory fails to give a correct qualitative picture of the thermodynamic behavior of the q-state Potts model when the exchange interaction is anisotropic in spin space. The correct picture is ... -
Quasi-one-dimensional magnetic properties of NiNb2−xVxO6 compounds synthesized at high pressure in a nonstandard columbite-type structure
Peña Pacheco, Jully Paola; Gusmao, Miguel Angelo Cavalheiro; Isnard, Olivier (2021) [Artigo de periódico]We report on the low-dimensional magnetic behavior of the series of compounds NiNb2−xVxO6 (0 x 2), with a columbite-type crystal structure stabilized at high pressure and temperature. Based on susceptibility, magnetization, ... -
Renormalization and phase transitions in Potts [fi]/sup 3/-field theory with quadratic and trilinear symmetry breaking
Barbosa, Marcia Cristina Bernardes; Gusmao, Miguel Angelo Cavalheiro; Theumann, Walter Karl (1986) [Artigo de periódico]Renormalized perturbation theory with generalized minimal subtraction is used as an appropriate renormalization-group procedure for the study of crossover behavior in the continuum version of the p-state Potts model with ... -
Simetrias mistas em supercondutividade (1999 a 2000)
Mota, André Hendler; Gusmao, Miguel Angelo Cavalheiro (2000) [Resumo publicado em evento] -
Simple approximation for the bethe ansatz solution of the one-dimensional fermi gas
Gusmao, Miguel Angelo Cavalheiro (1987) [Artigo de periódico]We present a simple approximation scheme for the solution of the integral equations resulting from the Bethe-ansatz diagonalization of the one-dimensional Fermi gas with ô-function attraction. These equations arise for the ... -
Simplified periodic anderson model : exact solution in infinite dimensions
Consiglio, Roberto; Gusmao, Miguel Angelo Cavalheiro (1997) [Artigo de periódico]We present a diagrammatic perturbative treatment of the hybridization for the periodic Anderson model that recovers the dynamical mean-field equations in the limit of infinite dimensions. The resulting effective singlesite ... -
Specific heat and magnetic order in LaMnO/sub 3+[delta]/
Ghivelder, Luis; Abrego-Castillo, Ildeman; Gusmao, Miguel Angelo Cavalheiro; Alonso, José Antônio; Cohen, Lesley F. (1999) [Artigo de periódico]Magnetic and specific-heat measurements are performed in three different samples of LaMnO₃₊[delta], with δ = 0.11, 0.15, and 0.26, presenting important disorder effects, such as carrier localization, due to high amounts ... -
Spin-density-wave instabilites for imperfectly nested fermi surfaces : application to bedt-ttf salts
Gusmao, Miguel Angelo Cavalheiro; Ziman, Timothy (1996) [Artigo de periódico]We discuss criteria for determining the optimal nesting vector from the maximum of the zero-field susceptibility for imperfectly nested Fermi surfaces. In particular, we present results for some of the bis(ethylenedithio) ... -
Superfluidez em estrelas de nêutrons : determinação da energia da gap
Espindola, Luciana da Silveira; Gusmao, Miguel Angelo Cavalheiro; Vasconcellos, Cesar Augusto Zen; Marranghello, Guilherme Frederico; Rocha, Sergio Souto (2001) [Resumo publicado em evento] -
Suppression of magnetic ordering in quasi-one-dimensional FexCo1−xNb2O6 compounds
Sarvezuk, Paulo Willian Carvalho; Kinast, Eder Julio; Colin, C. V.; Gusmao, Miguel Angelo Cavalheiro; Cunha, Joao Batista Marimon da; Isnard, Olivier (2011) [Artigo de periódico]We present a systematic investigation of the series of compounds FexCo1−xNb2O6 by means of x-ray and neutron powder diffraction combined with magnetic measurements, carried out in the paramagnetic as well as in the ordered ... -
Tight-binding treatment of the Hubband model in infinite dimensions
Craco, Luis; Gusmao, Miguel Angelo Cavalheiro (1996) [Artigo de periódico]We discuss the infinite dimension limit of the Hubbard model by means of a perturbative expansion of the one-particle Green’s function around the atomic limit. The diagrammatic structure is simplified in this limit, allowing ...