Electronic Structure And Origin Of Ferromagnetism In Ga 1-xmnxas Semiconductors

We perform a detailed theoretical study, within the density-functional theory, of the electronic structure and magnetic properties of Ga 1-xMnxAs diluted semiconductors. Ab initio total energy results provide evidence that the appearance of a ferromagnetic state in these materials is due to an exchange coupling between the localized ↑ S=52 Mn spins mediated by quasi-localized ↓ holes, with strong p-like character, surrounding the fully polarized Mn d5-electrons. From total energy differences, we find the effective Mn-Mn coupling always ferromagnetic, with the Mn-Mn interaction intermediated by an antiferromagnetic coupling of each Mn spin to the holes. © 2003 Elsevier B.V. All rights reserved.340-342874877Ohno, H., (1992) Phys. Rev. Lett., 68, p. 2664Ohno, H., (1996) Appl. Phys. Lett., 69, p. 363Matsukura, F., (1998) Phys. Rev. B, 57, pp. R2037Ohno, H., (1999) J. Magn. Magn. Mater., 200, p. 110Edmonds, K.W., (2002) Appl. Phys. Lett., 81, p. 3010Seong, M.J., (2002) Phys. Rev. B, 66, p. 033202Potashnik, S.J., (2001) Appl. Phys. Lett., 79, p. 1495Van Esch, A., (1997) Phys. Rev. B, 56, p. 13103Asklund, H., (2002) Phys. Rev. B, 66, p. 115319Yu, K.M., (2002) Phys. Rev. B, 65, pp. R201303Yu, K.M., (2002) Appl. Phys. Lett., 81, p. 844Moriya, R., Munekata, H., (2003) J. Appl. Phys., 93, p. 4603Potashnik, S.J., (2002) Phys. Rev. B, 66, p. 012408Hayashi, T., (2001) Appl. Phys. Lett., 78, p. 1691Dietl, T., (1997) Phys. Rev. B, 55, pp. R3347Ohno, H., Matsukura, F., (2001) Solid State Commun., 117, p. 179Vanderbilt, D., (1990) Phys. Rev. B, 41, p. 7892Kresse, G., Hafner, J., (1993) Phys. Rev. B, 47, pp. R558Kresse, G., Furthmuller, J., (1996) Phys. Rev. B, 54, p. 11169Kresse, G., Joubert, D., (1999) Phys. Rev. B, 59, p. 1758Chapman, R.A., Hutchinson, W.G., (1967) Phys. Rev. Lett., 18, p. 443Schneider, J., (1987) Phys. Rev. Lett., 59, p. 240Linnarsson, M., (1997) Phys. Rev. B, 55, p. 6938Singley, E.J., (2002) Phys. Rev. Lett., 89, p. 097203Dietl, T., (2001) Phys. Rev. B, 63, p. 195205Abolfath, M., (2001) Phys. Rev. B, 63, p. 054418Zhao, Y.-J., (2003) Phys. Rev. Lett., 90, p. 04720

First Principles Study Of The Ferromagnetism In Ga1-xmn Xas Semiconductors

We have performed ab initio calculations within the density-functional theory for Ga1-xMnxAs As diluted semiconductors. Total energy results unambiguously show that a quasi-localized ↓ hole, with predominant p-like character, surrounds the fully polarized Mn ↑ d 5-electrons. The calculations indicate that the holes form a relatively dispersionless impurity band, thus rendering effectivemass descriptions of hole states open to challenge. We obtain estimates both for the s = 1/2 hole and S = 5/2 Mn exchange coupling, and for the distance dependence of the effective Mn-Mn exchange interaction. The results demonstrate that the effective Mn-Mn coupling is always ferromagnetic, and thus non-RKKY, and is intermediated by the antiferromagnetic coupling of each Mn spin to the holes.164682438250Ohno, H., Munekata, H., Penney, T., Von Molnàr, S., Chang, L.L., (1992) Phys. Rev. Lett., 68, p. 2664Ohno, H., Shen, A., Matsukura, F., Oiwa, A., Endo, A., Katsumoto, S., Iye, Y., (1996) Appl. Phys. Lett., 69, p. 363Van Esch, A., Van Bockstal, L., De Boeck, J., Verbanck, G., Van Steenbergen, A.S., Wellmann, P.J., Grietens, B., Borghs, G., (1997) Phys. Rev. B, 56, p. 13103Matsukura, F., Ohno, H., Shen, A., Sugawara, Y., (1998) Phys. Rev. B, 57, pp. R2037Ohno, H., (1999) J. Magn. Magn. Mater., 200, p. 110Potashnik, S.J., Ku, K.C., Chun, S.H., Berry, J.J., Samarth, N., Schiffer, P., (2001) Appl. Phys. Lett., 79, p. 1495Edmonds, K.W., Wang, K.Y., Campion, R.P., Neumann, A.C., Foxon, C.T., Gallagher, B.L., Main, P.C., (2002) Appl. Phys. Lett., 81, p. 3010Seong, M.J., Chun, S.H., Cheong, H.M., Samarth, N., Mascarenhas, A., (2002) Phys. Rev. B, 66, p. 033202Asklund, H., Iliver, L., Kanski, J., Sadowski, J., (2002) Phys. Rev. B, 66, p. 115319Yu, K.M., Walukiewicz, W., Wojtowicz, T., Kuryliszyn, I., Liu, X., Sasaki, Y., Furdyna, J.K., (2002) Phys. Rev. B, 65, pp. R201303Yu, K.M., Walukiewicz, W., Wojtowicz, T., Lim, W.L., Liu, X., Sasaki, Y., Dobrowolska, M., Furdyna, J.K., (2002) Appl. Phys. Lett., 81, p. 844Potashnik, S.J., Ku, K.C., Mahendiran, R., Chun, S.H., Wang, R.F., Samarth, N., Schiffer, P., (2002) Phys. Rev. B, 66, p. 012408Moriya, R., Munekata, H., (2003) J. Appl. Phys., 93, p. 4603Dos Santos, R.R., Oliveira, L.E., D'Albuquerque e Castro, J., (2002) J. Phys.: Condens. Matter, 14, p. 3751Dos Santos, R.R., Oliveira, L.E., D'Albuquerque e Castro, J., (2003) J. Appl. Phys., 93, p. 1845Hayashi, T., Hashimoto, Y., Katsumoto, S., Iye, Y., (2001) Appl. Phys. Lett., 78, p. 1691Dietl, T., Haury, A., Merle D'Aubigné, Y., (1997) Phys. Rev. B, 55, pp. R3347Ohno, H., Matsukura, F., (2001) Solid State Commun., 117, p. 179Okabayashi, J., Kimura, A., Rader, O., Mizokawa, T., Fujimori, A., Hayashi, T., Tanaka, M., (2001) Phys. Rev. B, 64, p. 125304Singley, E.J., Kawakami, R., Awschalom, D.D., Basov, D.N., (2002) Phys. Rev. Lett., 89, p. 097203Dietl, T., Ohno, H., Matsukura, F., (2001) Phys. Rev. B, 63, p. 195205Abolfath, M., Jungwirth, T., Brum, J., MacDonald, A.H., (2001) Phys. Rev. B, 63, p. 054418Sanvito, S., Ordejón, P., Hill, N.A., (2001) Phys. Rev. B, 63, p. 165206Bouzerar, G., Kudrnovský, J., Berqvist, L., Bruno, P., (2003) Phys. Rev. B, 68, pp. 081203RSandratskii, L.M., Bruno, P., (2002) Phys. Rev. B, 66, p. 13443522nd Int. Conf. on Defects in Semiconductors (Aarhus, Denmark, 2003), , Preliminary results were presented at theDa Silva, A.J.R., Fazzio, A., Dos Santos, R.R., Oliveira, L.E., (2003) Physica B, 340-342, p. 874Vanderbilt, D., (1990) Phys. Rev. B, 41, p. 7892Kresse, G., Hafner, J., (1993) Phys. Rev. B, 47, pp. R558Kresse, G., Furthmüller, J., (1996) Phys. Rev. B, 54, p. 11169Kresse, G., Joubert, D., (1999) Phys. Rev. B, 59, p. 1758Linnarsson, M., Janzén, E., Monemar, B., Kleverman, M., Thilderkvist, A., (1997) Phys. Rev. B, 55, p. 6938Chapman, R.A., Hutchinson, W.G., (1967) Phys. Rev. Lett., 18, p. 443Schneider, J., Kaufmann, U., Wilkening, W., Baeumler, M., Kohl, F., (1987) Phys. Rev. Lett., 59, p. 240Zhao, Y.-J., Mahadevan, P., Zunger, A., (2004) Appl. Phys. Lett., 84, p. 3753Zhao, Y.-J., Shishidou, T., Freeman, A.J., (2003) Phys. Rev. Lett., 90, p. 047204Sanyal, B., Bengone, O., Mirbt, S., (2003) Phys. Rev. B, 68, p. 20521

Complejo respiratorio bovino: evidencia de circulación viral múltiple en un establecimiento de cría

El complejo respiratorio bovino (CRB) es una de las principales causas de pérdidas productivas en rodeos de cría, tambo y engorde a corral. Los agentes infecciosos involucrados incluyen virus, bacterias y micoplasmas. Dentro de los agentes virales se encuentran el virus respiratorio sincicial bovino (bRSV), el virus parainfluenza 3 bovino (BPIV3), el herpesvirus bovino tipo 1 (BoHV1) y el virus de la diarrea viral bovina (BVDV). El objetivo de este trabajo fue evaluar la circulación de los virus asociados al CRB en un rodeo de cría, durante el período posdestete, mediante un estudio serológico longitudinal. En forma complementaria, se describieron y compararon los hallazgos clínicos y hematológicos. Se seleccionaron 32 animales de 5 a 7 meses de edad, sin vacunación previa, y se evaluó diariamente la presencia de signos clínicos compatibles con CRB. Se extrajeron muestras de sangre los días 0 (destete), +14 y +25 (momento en que culminó el ensayo). No se detectaron animales con manifestación clínica de CRB y los parámetros hematológicos se encontraron dentro del rango de referencia. Al inicio de la experiencia, ningún animal presentaba anticuerpos (Ac) específicos para bRSV, mientras que para el resto de los agentes virales, el porcentaje de animales seropositivos fue variable: 53% (BVDV1a), 31% (BPIV3), 25% (BVDV2) y 13% (BoHV1). Al día +25 los porcentajes de seropositivos fueron los siguientes: 47% (BVDV1a), 50% (BPIV3), 19% (BVDV2), 25% (BoHV1) y 81% (bSRV). Los porcentajes de seroconversión para bRSV, BPIV3, BVDV1a y BoHV1 fueron 34%, 25%, 16% y 13%, respectivamente. Además, el 66% de los animales seroconvirtió a uno o más virus. Para BVDV2 y BVDV1b no se observó seroconversión. Estos resultados evidencian la circulación, e incluso en algunos casos la coinfección de los agentes virales involucrados en el CRB en e período posdestete. Resulta importante la realización de estudios virológicos complementarios que permitan identificar y caracterizar las cepas circulantes en esta etapa productiva, principalmente en relación con bSRV y PIV3, virus de los que se posee escasa información en nuestro medio

Renal cortex copper concentration in acute copper poisoning in calves

The aim of this study was to estimate the diagnostic value of renal cortex copper (Cu) concentration in clinical cases of acute copper poisoning (ACP). A total of 97 calves that died due to subcutaneous copper administration were compiled in eleven farms. At least, one necropsy was conducted on each farm and samples for complementary analysis were taken. The degree of autolysis in each necropsy was evaluated. The cases appeared on extensive grazing calf breeding and intensive feedlot farms, in calves of 60 to 200 kg body weight. Mortality varied from 0.86 to 6.96 %, on the farms studied. The first succumbed calf was found on the farms between 6 and 72 hours after the susbcutaneous Cu administration. As discrepancies regarding the reference value arose, the local value (19.9 parts per million) was used, confirming the diagnosis of acute copper poisoning in 93% of the analyzed kidney samples. These results confirm the value of analysis of the cortical kidney Cu concentration for the diagnosis of acute copper poisoning

Characteristics, management, and outcomes of patients with left‐sided infective endocarditis complicated by heart failure: a substudy of the ESC‐EORP EURO‐ENDO (European infective endocarditis) registry

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