Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in Ni81_{81}Fe19_{19} / α\alpha-Fe2_2O3_3

We report studies of exchange bias and coercivity in ferromagnetic Ni$_{81}$Fe$_{19}$ layers coupled to antiferromagnetic (AF) (0001), (11$\bar{2}$0), and (11$\bar{0}$2) $\alpha$-Fe$_2$O$_3$ layers. We show that AF spin configurations which permit spin-flop coupling give rise to a strong uniaxial anisotropy and hence a large coercivity, and that by annealing in magnetic fields parallel to specific directions in the AF we can control either coercivity or exchange bias. In particular, we show for the first time that a reversible temperature-induced spin reorientation in the AF can be used to control the exchange interaction.Comment: 15 pages, 5 figures, submitted to Phys. Rev. Let

Percolative phase separation induced by nonuniformly distributed excess oxygens

The zero-field $^{139}$La and $^{55}$Mn nuclear magnetic resonances were studied in $\rm La_{0.8}Ca_{0.2}MnO_{3+\delta}$ with different oxygen stoichiometry $\delta$. The signal intensity, peak frequency and line broadening of the $^{139}$La NMR spectrum show that excess oxygens have a tendency to concentrate and establish local ferromagnetic ordering around themselves. These connect the previously existed ferromagnetic clusters embedded in the antiferromagnetic host, resulting in percolative conduction paths. This phase separation is not a charge segregation type, but a electroneutral type. The magnetoresistance peak at the temperature where percolative paths start to form provides a direct evidence that phase separation is one source of colossal magnetoresistance effect.Comment: 4 pages, 5 figure

Effect of suppression of local distortion on magnetic, electrical and thermal transport properties of Cr substituted bi-layer manganite LaSr2_{2}Mn2_{2}O7_{7}

We have investigated magnetic, electrical and thermal transport properties (Seebeck effect and thermal conductivity) of LaSr$_{2}$Mn$_{2-y}$Cr$_{y}$O$_{7}$ polycrystalline samples ($y$=0.1, 0.2, 0.4 and 0.6). The Cr$^{3+}$ substitution for Mn$^{3+}$ sites causes a removal of $d_{x^2-y^2}$ orbital of $e_g$-electron resulting in a volume shrinkage of lattice. Magnetic measurements reveal the appearance of a glassy behavior for Cr-doped samples, accompanied by both a collapse of the A-type antiferromagnetic structure and the growth of ferromagnetic clusters. Cr-doping effect on electrical transport strongly enhances an insulating behavior over a wide range of temperature, while it suppresses a local minimum of thermoelectric power at lower temperatures. The phonon thermal conduction gradually rises with increasing Cr content, which is contradictory to a typical impurity effect on thermal conductivity. We attribute this to a suppression of local lattice distortion through the introduction of Jahn-Teller inactive ions of Cr$^{3+}$.Comment: 8 pages, 9figure

Pengaruh Komposisi Daun Gamal (Gliricidia sepium Hbr.) dan Kotoran Sapi dengan Nutrisi Pisang terhadap Rasio C/N Kompos

It has been done a research on the effect of the composition of gliricidia sepium Hbr. And cow dung with banana nutrition on the composting process on the C/N ratio. This research was conducted with the aim of knowing the effect of the composition and the length of time required for fermentation. Composting was made with a variety of cow dung : gliricidia sepium Hbr. In a ratio of 1:9, 1:1, 3:2, 7:3, 9:1, and 2:3 in % by using 25% banana nutrition and 100% water from the total weight of the manure. On this research was found that the optimal time is on 14th day with characteristic  of compost  that was produced, equal with the the Indonesia National Standar (SNI Kompos 19-7030-2004). The conclusion is the compcsition of cow dung and Gliricidia sepium leaves did not significant affect to the C/N compost ratio

Infections with Avian Pathogenic and Fecal Escherichia coli Strains Display Similar Lung Histopathology and Macrophage Apoptosis

The purpose of this study was to compare histopathological changes in the lungs of chickens infected with avian pathogenic (APEC) and avian fecal (Afecal) Escherichia coli strains, and to analyze how the interaction of the bacteria with avian macrophages relates to the outcome of the infection. Chickens were infected intratracheally with three APEC strains, MT78, IMT5155, and UEL17, and one non-pathogenic Afecal strain, IMT5104. The pathogenicity of the strains was assessed by isolating bacteria from lungs, kidneys, and spleens at 24 h post-infection (p.i.). Lungs were examined for histopathological changes at 12, 18, and 24 h p.i. Serial lung sections were stained with hematoxylin and eosin (HE), terminal deoxynucleotidyl dUTP nick end labeling (TUNEL) for detection of apoptotic cells, and an anti-O2 antibody for detection of MT78 and IMT5155. UEL17 and IMT5104 did not cause systemic infections and the extents of lung colonization were two orders of magnitude lower than for the septicemic strains MT78 and IMT5155, yet all four strains caused the same extent of inflammation in the lungs. The inflammation was localized; there were some congested areas next to unaffected areas. Only the inflamed regions became labeled with anti-O2 antibody. TUNEL labeling revealed the presence of apoptotic cells at 12 h p.i in the inflamed regions only, and before any necrotic foci could be seen. The TUNEL-positive cells were very likely dying heterophils, as evidenced by the purulent inflammation. Some of the dying cells observed in avian lungs in situ may also be macrophages, since all four avian E. coli induced caspase 3/7 activation in monolayers of HD11 avian macrophages. In summary, both pathogenic and non-pathogenic fecal strains of avian E. coli produce focal infections in the avian lung, and these are accompanied by inflammation and cell death in the infected areas

Evidence for Narrow N*(1685) Resonance in Quasifree Compton Scattering on the Neutron

The first study of quasi-free Compton scattering on the neutron in the energy range of $E_{\gamma}=0.75 - 1.5$ GeV is presented. The data reveals a narrow peak at $W\sim 1.685$ GeV. This result, being considered in conjunction with the recent evidence for a narrow structure at $W\sim 1.68$GeV in the $\eta$ photoproduction on the neutron, suggests the existence of a new nucleon resonance with unusual properties: the mass $M\sim 1.685$GeV, the narrow width $\Gamma \leq 30$MeV, and the much stronger photoexcitation on the neutron than on the proton.Comment: Replaced with the version published in Phys. Rev.

Social perception on Science and Technology in the northeastern provinces of Argentina.

Se presentan datos de la percepción social  de  la  Ciencia  y  la  Tecnología  de  los habitantes  de  la  región  nordeste  de  Argentina  que  reflejan  una  sociedad  con moderada  cultura  científica  y  tecnológica. La  cuestión  "que  imagen  tiene  de  la  ciencia"   se  utilizó  para  realizar  una valoración general donde más de la mitad de  los  encuestados  tuvo  una  opinión positiva.  Sin  embargo,  solo  el  14%  de  la muestra  considera  que  la  Ciencia  y  la Tecnología  mejoran  la  calidad  de  la  vida  humana.  Se  propone  la  generación  de cultura  científica  a  través  de  la  participación  de  los  actores  sociales involucrados,  estimulados  por  los  organismos  públicos  responsables  del desarrollo  científico  y  tecnológico.  Los  resultados  pueden  ser  utilizados  para  la toma  de  decisiones  bien informadas en  el  desenvolvimiento  social  y  la  participación ciudadana;  además,  para  orientar  la  política científica y tecnológica.This paper presents data related to the social perception of science and technology to the people of the northeast of Argentina of the country that reflect a society with moderate scientific and technological culture. The question "what image has of science" was used to make a general assessment where more than half of surveyed had a positive opinion. However, only 14% of the sample believes that science and technology improve the quality of human life.We propose the generation of scientific culture through the participation of the social actors involved, stimulated by public agencies responsible for the scientific and technological development. The results can be used for making informed decisions in the social development and citizen participation, in addition to guide scientific and technological policy.Fil: Juarez, Rolando Pablo. Universidad Nacional del Nordeste. Facultad de Odontologia. Secretaria de Investigacion. Gabinete de Inv.interd.de Prevencion Salud y Epidemologia; Argentina;Fil: Martinez, Sandra Edda. Universidad Nacional del Nordeste. Facultad de Odontologia. Departamento de Clinicas Integradas;Fil: Dho, María Silvina. Universidad Nacional del Nordeste. Facultad de Odontologia. Secretaria de Investigacion. Gabinete de Inv.interd.de Prevencion Salud y Epidemologia;Fil: Vaculik, Patricia. Universidad Nacional del Nordeste. Facultad de Odontologia. Secretaria de Investigacion. Gabinete de Inv.interd.de Prevencion Salud y Epidemologia;Fil: Llarens, Adriana N.. Universidad Nacional del Nordeste. Facultad de Odontologia. Secretaria de Investigacion. Gabinete de Inv.interd.de Prevencion Salud y Epidemologia;Fil: Cúndom, Juan M.. Universidad Nacional del Nordeste. Facultad de Odontologia. Secretaria de Investigacion. Gabinete de Inv.interd.de Prevencion Salud y Epidemologia;Fil: Almirón, María. Universidad Nacional del Nordeste. Facultad de Odontologia. Secretaria de Investigacion. Gabinete de Inv.interd.de Prevencion Salud y Epidemologia

Formation of finite antiferromagnetic clusters and the effect of electronic phase separation in Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}

We report the first experimental evidence of a magnetic phase arising due to the thermal blocking of antiferromagnetic clusters in the weakened charge and orbital ordered system Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}. The third order susceptibility (\chi_3) is used to differentiate this transition from a spin or cluster glass like freezing mechanism. These clusters are found to be mesoscopic and robust to electronic phase separation which only enriches the antiphase domain walls with holes at the cost of the bulk, without changing the size of these clusters. This implies that Al substitution provides sufficient disorder to quench the length scales of the striped phases.Comment: 4 Post Script Figure

Ripple modulated electronic structure of a 3D topological insulator

3D topological insulators, similar to the Dirac material graphene, host linearly dispersing states with unique properties and a strong potential for applications. A key, missing element in realizing some of the more exotic states in topological insulators is the ability to manipulate local electronic properties. Analogy with graphene suggests a possible avenue via a topographic route by the formation of superlattice structures such as a moir\'e patterns or ripples, which can induce controlled potential variations. However, while the charge and lattice degrees of freedom are intimately coupled in graphene, it is not clear a priori how a physical buckling or ripples might influence the electronic structure of topological insulators. Here we use Fourier transform scanning tunneling spectroscopy to determine the effects of a one-dimensional periodic buckling on the electronic properties of Bi2Te3. By tracking the spatial variations of the scattering vector of the interference patterns as well as features associated with bulk density of states, we show that the buckling creates a periodic potential modulation, which in turn modulates the surface and the bulk states. The strong correlation between the topographic ripples and electronic structure indicates that while doping alone is insufficient to create predetermined potential landscapes, creating ripples provides a path to controlling the potential seen by the Dirac electrons on a local scale. Such rippled features may be engineered by strain in thin films and may find use in future applications of topological insulators.Comment: Nature Communications (accepted

Unusual magnetic relaxation behavior in La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3

We have carried out a systematic magnetic relaxation study, measured after applying and switching off a 5 T magnetic field to polycrystalline samples of La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3. The long time logarithmic relaxation rate (LTLRR), decreased from 10 K to 150 K and increased from 150 K to 195 K in La0.5Ca0.5MnO3. This change in behavior was found to be related to the complete suppression of the antiferromagnetic phase above 150 K and in the presence of a 5 T magnetic field. At 195 K, the magnetization first decreased, and after a few minutes increased slowly as a function of time. Moreover, between 200 K and 245 K, the magnetization increased throughout the measured time span. The change in the slope of the curves, from negative to positive at about 200 K was found to be related to the suppression of antiferromagnetic fluctuations in small magnetic fields. A similar temperature dependence of the LTLRR was found for the Nd0.5Sr0.5MnO3 sample. However, the temperature where the LTLRR reached the minimum in Nd0.5Sr0.5MnO3 was lower than that of La0.5Ca0.5MnO3. This result agrees with the stronger ferromagnetic interactions that exist in Nd0.5Sr0.5MnO3 in comparison to La0.5Ca0.5MnO3. The above measurements suggested that the general temperature dependence of the LTLRR and the underlying physics were mainly independent of the particular charge ordering system considered. All relaxation curves could be fitted using a logarithmic law at long times. This slow relaxation was attributed to the coexistence of ferromagnetic and antiferromagnetic interactions between Mn ions, which produced a distribution of energy barriers.Comment: Accepted to PRB as a regular article, 10 figures, Scheduled Issue: 01 June 200