Magnetic And Magnetocaloric Properties On The U1-y Ry Ga2 (r=er And Dy) Compound

The magnetic, calorimetric, and magnetocaloric properties of the pseudobinary U1-y Ry Ga2 (R=Er and Dy) series were studied to determine its potential as a candidate for use in cryogenic magnetic refrigeration. The partial substitution of Dy and Er for U provides a wide range of the ordering temperature and increases the saturation magnetic moment. The results for U1-y Dyy Ga2 with 0.6<y<0.9 show evidences of a spin-glass-like (SG) behavior, possibly as a consequence of competing anisotropy and exchange interactions within a frustrated hexagonal spin lattice. The isothermal magnetic entropy change (Δ Smag) observed for U Ga2 shows a well defined peak centered on TC, which is gradually broadened and shifted to lower temperatures as the Er and Dy content increases. For low concentrations (0.2≤y≤0.4) a tablelike profile is observed in the Δ Smag curve. © 2008 American Institute of Physics.1037Gschneidner Jr., K.A., Pecharsky, V.K., Tsokol, A.O., (2005) Radiat. Prot. Dosim., 68, p. 1479Bruck, E., (2005) J. Phys. D, 38, p. 381Yu, B.F., Gao, Q., Zhang, B., Meng, X.Z., Chen, Z., (2003) Int. J. Refrig., 26, p. 622Gschneidner Jr., K.A., Pecharsky, A.O., Pecharsky, V.K., (2001), 11, p. 433. , Cryoolers (Academic-Plenum, New York), Vol.,Smaili, A., Chahine, R., (1996) Adv. Cryog. Eng., 42, p. 445Hashimoto, T., Kuzuhura, T., Sahashi, M., Inomata, K., Tomokiyo, A., Yayama, H., (1987) J. Appl. Phys., 62, p. 3873Lima, A.L., Gschneidner Jr., K.A., Pecharsky, V.K., Pecharsky, A.O., (2003) Phys. Rev. B, 68, p. 134409De Oliveira, N.A., Von Ranke, P.J., (2003) J. Magn. Magn. Mater., 264, p. 55Tsai, T.H., Sellmyer, D.J., (1979) Phys. Rev. B, 20, p. 4577Doukouŕ, M., Gignoux, D., (1982) J. Magn. Magn. Mater., 30, p. 111Gignoux, D., Schimitt, D., Takeuchi, A., Zhang, F.Y., (1991) J. Magn. Magn. Mater., 97, p. 15Andreev, A.V., Belov, K.P., Deryagin, A.V., Levitin, R.Z., Menovsky, M., (1979) J. Phys. Colloq., 4, p. 82Mydosh, J.A., (1993), Spin Glasses: An Experimental Introduction (Taylor&Francis, London)Markin, P.E., Baranov, N.V., Sinitsyn, E.V., (1991) Physica B, 168, p. 19

Black hole collision with a scalar particle in four, five and seven dimensional anti-de Sitter spacetimes: ringing and radiation

In this work we compute the spectra, waveforms and total scalar energy radiated during the radial infall of a small test particle coupled to a scalar field into a $d$-dimensional Schwarzschild-anti-de Sitter black hole. We focus on $d=4, 5$ and 7, extending the analysis we have done for $d=3$. For small black holes, the spectra peaks strongly at a frequency $\omega \sim d-1$, which is the lowest pure anti-de Sitter (AdS) mode. The waveform vanishes exponentially as $t \to \infty$, and this exponential decay is governed entirely by the lowest quasinormal frequency. This collision process is interesting from the point of view of the dynamics itself in relation to the possibility of manufacturing black holes at LHC within the brane world scenario, and from the point of view of the AdS/CFT conjecture, since the scalar field can represent the string theory dilaton, and 4, 5, 7 are dimensions of interest for the AdS/CFT correspondence.Comment: 16 pages, 13 figures. Published versio

Magnetocaloric Effect And Evidence Of Superparamagnetism In Gda L2 Nanocrystallites: A Magnetic-structural Correlation

The correlation between structural and magnetic properties of GdAl2, focusing on the role played by the disorder in magnetic ordering and how it influences the magnetocaloric effect (MCE) are discussed. Micrometric-sized particles, consisting of nanocrystallites embedded in an amorphous matrix, were prepared by a mechanical milling technique and characterized by means of x-ray diffraction, scanning and high-resolution transmission electron microscopy as well as magnetic measurements as a function of an applied external magnetic field and temperature. The results show that the average particle size is just slightly diminished (≈7%) with the milling time (between 3 and 13 h), whereas the average crystallite size undergoes an expressive reduction (≈43%). For long milling times, structural disorders mostly associated with crystallite size singularly affect the magnetic properties, leading to a large tablelike MCE in the temperature range between 30 and 165 K. Below 30 K, nanocrystallites with dimensions below a given critical size cause an enhancement in the magnetic entropy change related to superparamagnetic behavior. In contrast, for low milling times, relative cooling power values are improved. These striking features along with the small magnetic hysteresis observed make the milled GdAl2 a promising material for application in the magnetic refrigeration technology. Finally, a discussion in an attempt to elucidate the origin of the spin-glass states previously reported in the literature for mechanically milled GdAl2 samples for very long times (400 and 1000 h) is presented. © 2016 American Physical Society.93

Magnetization And Specific Heat In U 1-xla Xga 2 And Magnetocaloric Effect In Uga 2

We have investigated the properties of the ferromagnetic series U1-x Lax Ga2. The magnetization results show a reduction of μeff and of Tc when x is increased. The electronic coefficient γ of the specific heat increases to a maximum of 260 mJUmol K2 at x=0.75. This behavior is probably consequence of delocalization of 5f electrons, causing enhancement of the density of states. For x=0.9 the ordering disappears and a non-Fermi-liquid behavior is observed. U Ga2 also presented a significant magnetocaloric effect of Δ Smag =-3.5 Jkg K at 120 K and H=7 T which can be modified by chemical pressure. © 2005 American Institute of Physics.9710Andeev, A.V., Belov, K.P., Deriagin, A.V., Levitin, R.Z., Menovsky, A., (1979) J. Phys. Colloq., 4, p. 82Da Silva, L.M., Gandra, F.G., Rojas, D.P., Cardoso, L.P., Medina, A.N., (2002) Physica B, 312-313, p. 906Tran, V.H., Kaczorowski, D., Roisnel, T., Tróc, R., Noel, H., Bouŕe, F., Andŕ, G., (1995) Physica B, 205, p. 24Gandra, F.G., Rojas, D.P., Shlyk, L., Cardoso, L.P., Medina, A.N., (2001) J. Magn. Magn. Mater., 226, p. 1312Barbara, B., (1973) J. Phys. (Paris), 34, p. 1039Sechovsky, V., Havela, L., Svoboda, P., (1986) J. Less-Common Met., 121, p. 163Segal, E., Wallace, W.E., (1975) J. Solid State Chem., 13, p. 201Radwanski, R.J., Kim-Ngan, N.H., (1995) J. Magn. Magn. Mater., 140, p. 1373Zapf, V.S., Dickey, R.P., Freeman, E.J., Sirvent, C., Maple, M.B., (2002) Phys. Rev. B, 65, p. 024437Pecharsky, V.K., Gschneider Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494Pecharsky, V.K., Gschneider Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494Plackowski, T., Junod, A., Bouquet, F., Sheikin, I., Wang, Y., Jezÿowski, A., Mattenberger, K., (2003) Phys. Rev. B, 67, p. 184406Svobodaa, P., Sechovsky, V., Menovsky, A.A., (2003) Physica B, 339, p. 177Gama, S., Coelho, A.A., De Campos, A., Carvalho, A.M.G., Gandra, F.G., Von Ranke, P.J., De Oliveira, N.A., Phys. Rev. Lett

Antropoceno na Amazônia: A dinâmica do uso e cobertura da terra do município de Garrafão do Norte, Pará, Brasil: Anthropocene in the Amazon: The dynamics of land use and land cover in the municipality of Garrafão do Norte, Pará, Brazil

O presente trabalho analisou as mudanças de uso e cobertura da terra na localidade, de forma espacial e temporal, nos anos de 2000 e 2020, por meio da plataforma Google Earth Engine (GEE). Utilizou-se a imagem do satélite Landsat-5/TM relativo ao ano de 2000 e imagem do satélite Landsat-8/OLI-TIRS referente ao ano de 2020. Os resultados apontam que houve uma redução de 135,91 km² de cobertura vegetal, correspondendo a 10,51% de perda proveniente das atividades antrópicas que ocorreram em Garrafão do Norte, especialmente, em relação à agricultura com os cultivos de dendê, mandioca e laranja e à pecuária com as pastagens, pois juntos apresentam um aumento de 198,06% que equivalem a 305,02 km² de área antropizada. Portanto verificou-se que o município de Garrafão do Norte segue o padrão de desenvolvimento econômico dos municípios amazônicos, onde acontece a diminuição das áreas florestais para a ampliação de suas atividades produtivas, como o cultivo de dendê, sendo este um dos principais geradores do desflorestamento da região, caracterizando o cenário do Antropoceno na Amazônia. This study analyzed changes in land use and land cover in the area, spatially and temporally, between 2000 and 2020, using the Google Earth Engine (GEE) platform. The Landsat-5/TM satellite image for the year 2000 and the Landsat-8/OLI-TIRS satellite image for the year 2020 were used. The results indicate a reduction of 135.91 km² of vegetation cover, corresponding to a 10.51% loss resulting from human activities that occurred in Garrafão do Norte, especially in relation to agriculture with oil palm, cassava and orange crops and livestock with pastures, as together they represent an increase of 198.06%, equivalent to 305.02 km² of human-altered area. Therefore, it was found that the municipality of Garrafão do Norte follows the economic development pattern of Amazonian municipalities, where there is a reduction in forest areas to expand their productive activities, such as palm oil cultivation, which is one of the main generators of deforestation in the region, characterizing the Anthropocene scenario in the Amazon