Fragility of ferromagnetic double exchange interactions and pressure tuning of magnetism in 3d-5d double perovskite Sr2FeOsO6

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOThe ability to tune exchange (magnetic) interactions between 3d transition metals in perovskite structures has proven to be a powerful route to discovery of novel properties. Here we demonstrate that the introduction of 3d-5d exchange pathways in double perovskites enables additional tunability, a result of the large spatial extent of 5d wave functions. Using x-ray probes of magnetism and structure at high pressure, we show that compression of Sr2FeOsO6 drives an unexpected continuous change in the sign of Fe-Os exchange interactions and a transition from antiferromagnetic to ferrimagnetic order. We analyze the relevant electron-electron interactions, shedding light into fundamental differences with the more thoroughly studied 3d-3d systems.The ability to tune exchange (magnetic) interactions between 3d transition metals in perovskite structures has proven to be a powerful route to discovery of novel properties. Here we demonstrate that the introduction of 3d-5d exchange pathways in double perovskites enables additional tunability, a result of the large spatial extent of 5d wave functions. Using x-ray probes of magnetism and structure at high pressure, we show that compression of Sr2FeOsO6 drives an unexpected continuous change in the sign of Fe-Os exchange interactions and a transition from antiferromagnetic to ferrimagnetic order. We analyze the relevant electron-electron interactions, shedding light into fundamental differences with the more thoroughly studied 3d-3d systems.912317FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO2013/14338-3Work at Argonne is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. L.S.I.V. is supported by FAPESP (SP-Brazil) under Contract No. 2013/14338-3. M.v.V. was supported by DOE-BES under Grant No. DE-FG02-03ER46097. This research was supported in part by the World Premier International Research Center of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, the Japan Society for the Promotion of Science (JSPS) through a Grant-in-Aid for Scientific Research (25289233). We would like to thank Changyong Park and Curtis Kenney-Benson for their assistance at 16-BM-D beamline, Sergey N. Tkachev for assistance with gas loading, and Richard Rosenberg for help with soft x-ray measurements. We also thank GSECARS for use of the gas loading and laser drilling facilities

On the chromospheric activity of stars with planets

Context. Signatures of chromospheric activity enhancement have been found for a dozen stars, pointing to a possible star-planet interaction. Nevertheless in the coronal activity regime, there is no conclusive observational evidence for such an interaction. Does star-planet interaction manifest itself only for a few particular cases, without having a major effect on stars with planets in general? Aims. We aim to add additional observational constraints to support or reject the major effects of star-planet interactions in stellar activity, based on CaII chromospheric emission flux. Methods. We performed a statistical analysis of CaII emission flux of stars with planets, as well as a comparison between CaII and X-ray emission fluxes, searching for dependencies on planetary parameters. Results. In the present sample of stars with planets, there are no significant correlations between chromospheric activity indicator log(R'HK) and planetary parameters. Further, the distribution of the chromospheric activity indicator for stars without planets is not distinguishable from the one with planets.Comment: 6 pages, 5 figures, submitted to A&

Generalized Heisenberg Algebras and Fibonacci Series

We have constructed a Heisenberg-type algebra generated by the Hamiltonian, the step operators and an auxiliar operator. This algebra describes quantum systems having eigenvalues of the Hamiltonian depending on the eigenvalues of the two previous levels. This happens, for example, for systems having the energy spectrum given by Fibonacci sequence. Moreover, the algebraic structure depends on two functions f(x) and g(x). When these two functions are linear we classify, analysing the stability of the fixed points of the functions, the possible representations for this algebra.Comment: 24 pages, 2 figures, subfigure.st

Características da carcaça de cordeiros submetidos a dietas com níveis de torta de dendê (Palmiste).

O objetivo com esse experimento foi avaliar o melhor nível de torta de dendê na dieta por intermédio das características de carcaça de ovinos confinados. Trinta e dois cordeiros inteiros, Santa Inês, com em media 6 meses, e 22 kg PV foram utilizados. Os níveis de torta de dendê (0; 7; 14 e 21 % da matéria seca) foram adicionadas ao concentrado. Após 70 dias de confinamento os animais foram abatidos e as características de carcaças foram mensuradas. O peso vivo ao abate e peso do corpo vazio não foram influenciados pelos níveis de torta de dendê; o peso da carcaça quente