1,534 research outputs found
Controlled switching between paramagnetic and diamagnetic Meissner effect in Pb/Co nanocomposites
A hybrid system which consists of a superconducting (SC) Pb film (100 nm
thickness) containing 1 vol% single domain ferromagnetic (FM) Co
particles of mean-size 4.5 nm reveal unusual magnetic properties: (i) a
controlled switching between the usual diamagnetic and the unusual paramagnetic
Meissner effect in field cooling as well as in zero-field cooling experiments
(ii) amplification of the positive magnetization when the sample enters the SC
state below T. These experimental findings can be explained by the
formation of spontaneous vortices and the possible alignment of these vortices
due to the foregoing alignment of the Co particle FM moments by an external
magnetic field.Comment: 5 pages, 3 figure
High coercivity induced by mechanical milling in cobalt ferrite powders
In this work we report a study of the magnetic behavior of ferrimagnetic
oxide CoFe2O4 treated by mechanical milling with different grinding balls. The
cobalt ferrite nanoparticles were prepared using a simple hydrothermal method
and annealed at 500oC. The non-milled sample presented coercivity of about 1.9
kOe, saturation magnetization of 69.5 emu/g, and a remanence ratio of 0.42.
After milling, two samples attained coercivity of 4.2 and 4.1 kOe, and
saturation magnetization of 67.0 and 71.4 emu/g respectively. The remanence
ratio MR/MS for these samples increase to 0.49 and 0.51, respectively. To
investigate the influence of the microstructure on the magnetic behavior of
these samples, we used X-ray powder diffraction (XPD), transmission electron
microscopy (TEM), and vibrating sample magnetometry (VSM). The XPD analysis by
the Williamson-Hall plot was used to estimate the average crystallite size and
strain induced by mechanical milling in the samples
Training-induced inversion of spontaneous exchange bias field on La1.5Ca0.5CoMnO6
In this work we report the synthesis and structural, electronic and magnetic
properties of La1.5Ca0.5CoMnO6 double-perovskite. This is a re-entrant spin
cluster material which exhibits a non-negligible negative exchange bias effect
when it is cooled in zero magnetic field from an unmagnetized state down to low
temperature. X-ray powder diffraction, X-ray photoelectron spectroscopy and
magnetometry results indicate mixed valence state at Co site, leading to
competing magnetic phases and uncompensated spins at the magnetic interfaces.
We compare the results for this Ca-doped material with those reported for the
resemblant compound La1.5Sr0.5CoMnO6, and discuss the much smaller spontaneous
exchange bias effect observed for the former in terms of its structural and
magnetic particularities. For La1.5Ca0.5CoMnO6, when successive magnetization
loops are carried, the spontaneous exchange bias field inverts its sign from
negative to positive from the first to the second measurement. We discuss this
behavior based on the disorder at the magnetic interfaces, related to the
presence of a glassy phase. This compound also exhibits a large conventional
exchange bias, for which there is no sign inversion of the exchange bias field
for consecutive cycles
Ferromagnetic resonance study of sputtered NiFe/V/NiFe heterostructures
AbstractThe Ni81Fe19/V/Ni81Fe19 heterostructures has been produced by magnetron sputtering and analyzed by ferromagnetic resonance. Two systems were investigated: the non symmetrical NiFe(50Å)/V(t)/NiFe(30Å) trilayers and the symmetrical NiFe(80Å)/V(t)/NiFe(80Å) trilayers, with variable ultrathin V thickness t. Ferromagnetic exchange coupling was evidenced for t below 10Å by the excitation of the optic mode, in the case of the non symmetrical samples, and by the observation of a single resonance mode for the symmetrical trilayers. For larger V thickness, all samples exhibited two modes, which were attributed to the resonance of the individual NiFe layers with different effective magnetizations. The analysis with the equilibrium and resonance conditions provided the exchange coupling constants and effective magnetizations
Correlation between Gamma-Ray bursts and Gravitational Waves
The cosmological origin of -ray bursts (GRBs) is now commonly
accepted and, according to several models for the central engine, GRB sources
should also emit at the same time gravitational waves bursts (GWBs). We have
performed two correlation searches between the data of the resonant
gravitational wave detector AURIGA and GRB arrival times collected in the BATSE
4B catalog. No correlation was found and an upper limit \bbox{} on the averaged amplitude of gravitational waves
associated with -ray bursts has been set for the first time.Comment: 7 pages, 3 figures, submitted to Phys. Rev.
Propriedades físicas e químicas e rendimentos da destilação seca da madeira de Grevillea robusta.
bitstream/CNPF-2009-09/15736/1/circ-tec40.pd
Effect of shape, gluten, and mastication effort on in vitro starch digestion and the predicted glycemic index of pasta
Gluten-containing (GC) and gluten-free (GF) pasta consumption has been growing in recent years. The market offers a wide variety of pasta types, with differences in shape and formulation that influence the mastication process and, consequently, their nutritional behaviors (i.e. starch digestibility and glycemic response). This study investigated the effect of shape, gluten, and structural breakdown on in vitro starch digestibility and predicted the glycemic index (pGI) of GC and GF penne, spaghetti, and risoni. Pasta was cooked and minced to mimic short, intermediate, and long mastication efforts. Short mastication led to a higher number of big particles than intermediate and long mastications for all pasta samples, which was reflected in the different starch digestibility and pGI patterns. Multivariate analysis of variance showed that the three studied factors differently affected the in vitro starch digestion of pasta. Mastication effort, shape, and their interaction mainly affected the starch digestion rate and pGI. Gluten was the major factor in affecting the amount of digested starch. The results suggested that small shapes (i.e. risoni), the presence of gluten, and short mastication effort led to a lower pGI. The findings will be useful for the development of pasta products tailored to fulfill the needs of specific consumers following a rational food design approach
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