Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates

In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly-doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures. The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples. The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in the non-saturated regime confirming the low field microwave absorption (LFMA), were correlated to the peaks and slopes found in the magnetoresistance curves. The results suggest long range spin injection and detection in low resistive silicon and the magnetic resonance technique is herein introduced as a promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure

A Possible Dynamical Effect of a Primordial Magnetic Field

The possible existence of a primordial magnetic field in the universe has been previously investigated in many articles. Studies involving the influence of a magnetic field in the nucleosyntesis era, studies considering the effects in the formation of structures during the radiation era and the matter era have been considered. We here assume the existence of a primordial magnetic field and study its effect, in particular, in the formation of voids. The study is twofold: to put constraints on the strength of the magnetic field during the recombination era and to preview its effects on the formation of voids.Comment: 21 pages, aasms4.sty AAS Latex V4.0 file, 3 EPS figures included. Also available at http://www.iagusp.usp.br/ To appear in the Ap

A sustainable system for animal production in the brazilian semi-arid region.

In the semi-arid Northeast, there are about 1.0 million of farming units. Such units operate on a region characterized by heavy constraints in tenns of soil and water resources. The production systems show a low technological pattem, in sufficient to achieve an appropriate standard of living for the farmer, and, to avoid the continuous deterioration of the natural resources, mainly of the caatinga vegetation. Some studies have shown that the subsistence type of agriculture today practiced, only is successful on three in every ten years, and that livestock production, by its lower vulnerability to drought effects, has constituted the main anti-migration factor in the semi-and region. Results of a recent study conducted by Embrapa Semi-Arid workers, including small farms of 107 counties, confrrmed that trend, showing a gross income increase as livestock participation in the farm activities becomes higher. Research on livestock Production in Nontheast has generated a vast number of technologies, which, if adequately combined and operated, can assure, with no environrnental damage, economical levels of productivity and a more equitable distribution of the benefits

Experimental and theoretical evidences for the ice regime in planar artificial spin ices

In this work, we explore a kind of geometrical effect in the thermodynamics of artificial spin ices (ASI). In general, such artificial materials are athermal. Here, We demonstrate that geometrically driven dynamics in ASI can open up the panorama of exploring distinct ground states and thermally magnetic monopole excitations. It is shown that a particular ASI lattice will provide a richer thermodynamics with nanomagnet spins experiencing less restriction to flip precisely in a kind of rhombic lattice. This can be observed by analysis of only three types of rectangular artificial spin ices (RASI). Denoting the horizontal and vertical lattice spacings by a and b, respectively, then, a RASI material can be described by its aspect ratio $\gamma$=a/b. The rhombic lattice emerges when $\gamma$=$\sqrt{3}$. So, by comparing the impact of thermal effects on the spin flips in these three appropriate different RASI arrays, it is possible to find a system very close to the ice regime