Anomalous Hall Effect in three ferromagnets: EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30

The Hall resistivity (Rho_xy), resistivity (Rho_xx), and magnetization of three metallic ferromagnets are investigated as a function of magnetic field and temperature. The three ferromagnets, EuFe4Sb12 (Tc = 84 K), Yb14MnSb11 (Tc = 53 K), and Eu8Ga16Ge30 (Tc = 36 K) are Zintl compounds with carrier concentrations between 1 x 10^21 cm^-3 and 3.5 x 10^21 cm^-3. The relative decrease in Rho_xx below Tc [Rho_xx(Tc)/Rho_xx(2 K)] is 28, 6.5, and 1.3 for EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30 respectively. The low carrier concentrations coupled with low magnetic anisotropies allow a relatively clean separation between the anomalous (Rho_'xy), and normal contributions to the measured Hall resistivity. For each compound the anomalous contribution in the zero field limit is fit to alpha Rho_xx + sigma_xy rho_xx^2 for temperatures T < Tc. The anomalous Hall conductivity, sigma_xy, is -220 +- 5 (Ohm^-1 cm^-1), -14.7 +- 1 (Ohm^-1 cm^-1), and 28 +- 3 (Ohm^-1 cm^-1) for EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30 respectively and is independent of temperature for T < Tc if the change in spontaneous magnetization (order parameter) with temperature is taken into account. These data are consistent with recent theories of the anomalous Hall effect that suggest that even for stochiometric ferromagnetic crystals, such as those studied in this article, the intrinsic Hall conductivity is finite at T = 0, and is a ground state property that can be calculated from the electronic structure.Comment: 22 pages, 13 figures Submitted to PR

Relativistic free-particle quantization on the light-front: New aspects

We use the light-front machinery to study the behavior of a relativistic free particle and obtain the quantum commutation relations from the classical Poisson brackets. We argue that the usual projection onto the light-front coordinates for these from the covariant commutation ralations does not reproduce the expected results.Comment: To appear in the proceedings "IX Hadron Physics and VII Relativistic Aspects of Nuclear Physics: A Joint Meeting on QCD and QGP, Hadron Physics-RANP,2004,Angra dos Reis, Rio de Janeiro,Brazi

Surprises in the relativistic free-particle quantization on the light-front

We use the light front ``machinery'' to study the behavior of a relativistic free particle and obtain the quantum commutation relations from the classical Poisson brackets. We argue that their usual projection onto the light-front coordinates from the covariant commutation relations show that there is an inconsistency in the expected correlation between canonically conjugate variables ``time'' and ``energy''. Moreover we show that this incompatibility originates from the very definition of the Poisson brackets that is employed and present a simple remedy to this problem and envisages a profound physical implication on the whole process of quantization.Comment: 13 page

Magnetic Excitations in the S=1/2 Alternating Chain Compound (VO)_2P_2O_7

Magnetic excitations in an array of (VO)_2P_2O_7 single crystals have been measured using inelastic neutron scattering. Until now, (VO)_2P_2O_7 has been thought of as a two-leg antiferromagnetic Heisenberg spin ladder with chains running in the a-direction. The present results show unequivocally that (VO)_2P_2O_7 is best described as an alternating spin-chain directed along the crystallographic b-direction. In addition to the expected magnon with magnetic zone-center energy gap \Delta = 3.1 meV, a second excitation is observed at an energy just below 2\Delta. The higher mode may be a triplet two-magnon bound state.Comment: 4 pages, postscript figure

O processo de educação patrimonial como instrumento de auxílio na gestão dos bens patrimoniais

O presente artigo, de corte qualitativo, visa caracterizar a pr&aacute;tica da educa&ccedil;&atilde;o patrimonial como um processo que pode fortalecer e consolidar a preserva&ccedil;&atilde;o e conserva&ccedil;&atilde;o de bens patrimoniais, configurando dessa forma um instrumento de gest&atilde;o do patrim&ocirc;nio. Defendese, neste trabalho, que as a&ccedil;&otilde;es de restaura&ccedil;&atilde;o e conserva&ccedil;&atilde;o dos bens patrimoniais precisam encontrar suporte na comunidade que lhe serve de alicerce a fim de que tais a&ccedil;&otilde;es tenham resultados mais eficazes. Este trabalho oferece uma revis&atilde;o bibliogr&aacute;fica que explicita os conceitos e prop&oacute;sitos da educa&ccedil;&atilde;o patrimonial, assim como a import&acirc;ncia da apropria&ccedil;&atilde;o por parte da comunidade receptora dos seus bens patrimoniais de modo que as a&ccedil;&otilde;es de restauro e conserva&ccedil;&atilde;o sejam mais significativas para aquela atrav&eacute;s da inclus&atilde;o destes processos em atividades educativas. Toma-se como refer&ecirc;ncia a experi&ecirc;ncia realizada em 2008 pela equipe do Programa de Especializa&ccedil;&atilde;o em Patrim&ocirc;nio, da Diretoria de Preserva&ccedil;&atilde;o Cultural da FUNDARPE (&oacute;rg&atilde;o executor da pol&iacute;tica cultural do Estado, respons&aacute;vel pelas a&ccedil;&otilde;es de preserva&ccedil;&atilde;o e conserva&ccedil;&atilde;o do patrim&ocirc;nio). Atrav&eacute;s do Programa Monumenta (UNESCO), foi desenvolvido o Projeto &ldquo;Educa&ccedil;&atilde;o Patrimonial para os munic&iacute;pios de Goiana e Igarassu, em Pernambuco&rdquo;. O Programa Monumenta atua em cidades hist&oacute;ricas protegidas pelo Instituto do Patrim&ocirc;nio Hist&oacute;rico e Art&iacute;stico Nacional (Iphan), promovendo obras de restaura&ccedil;&atilde;o e recupera&ccedil;&atilde;o de bens tombados, aliadas a a&ccedil;&otilde;es de educa&ccedil;&atilde;o patrimonial. O projeto desenvolvido pela FUNDARPE, dividido em v&aacute;rias etapas, englobou a realiza&ccedil;&atilde;o de diagn&oacute;stico dos problemas encontrados relativos aos bens patrimoniais nos munic&iacute;pios; mapeamento dos patrim&ocirc;nios e seus estados de conserva&ccedil;&atilde;o; realiza&ccedil;&atilde;o de um Encontro de Educa&ccedil;&atilde;o Patrimonial composto de oficinas e palestras e cria&ccedil;&atilde;o de uma publica&ccedil;&atilde;o direcionada para a educa&ccedil;&atilde;o patrimonial em cada munic&iacute;pio. Dentre os principais resultados atingidos com a execu&ccedil;&atilde;o do projeto, ressaltam-se a import&acirc;ncia de a&ccedil;&otilde;es no campo da educa&ccedil;&atilde;o patrimonial n&atilde;o apenas como forma de aproxima&ccedil;&atilde;o da comunidade dos seus bens patrimoniais, como tamb&eacute;m uma estrat&eacute;gia para tornar mais efetiva as a&ccedil;&otilde;es de restauro e conserva&ccedil;&atilde;o realizadas pelas institui&ccedil;&otilde;es oficiais de preserva&ccedil;&atilde;o do patrim&ocirc;nio.Tópico 1: Aspectos teóricos, históricos, legales, económicos y tecnológicos de la restauración y conservación de bienes patrimoniales

Surveillance on the light-front gauge fixing Lagrangians

In this work we propose two Lagrange multipliers with distinct coefficients for the light-front gauge that leads to the complete (non-reduced) propagator. This is accomplished via $(n\cdot A)^{2}+(\partial \cdot A)^{2}$ terms in the Lagrangian density. These lead to a well-defined and exact though Lorentz non invariant light front propagator.Comment: 7 pages. This is an improved version of hep-th/030406

Quasi-one-dimensional magnons in an intermetallic marcasite

We present inelastic neutron scattering measurements and first principles calculations examining the intermetallic marcasite CrSb2. The observed spin wave dispersion implies that the magnetic interactions are strongly one-dimensional with antiferromagnetic chains parallel to the crystalline c-axis. Such low-dimensional excitations are unexpected in a semiconducting intermetallic system. Moreover this material may be further interesting in that the magnetic anisotropy may enhance thermoelectric properties along particular crystallographic directions.Comment: 5 pages, 4 figures, Submitted to an APS journa