Single spin-torque vortex oscillator using combined bottom-up approach and e-beam lithography

A combined bottom-up assembly of electrodeposited nanowires and electron beam lithography technique has been developed to investigate the spin transfer torque and microwave emission on specially designed nanowires containing a single Co/Cu/Co pseudo spin valve. Microwave signals have been obtained even at zero magnetic field. Interestingly, high frequency vs. magnetic field tunability was demonstrated, in the range 0.4 - 2 MHz/Oe, depending on the orientation of the applied magnetic field relative to the magnetic layers of the pseudo spin valve. The frequency values and the emitted signal frequency as a function of the external magnetic field are in good quantitative agreement with the analytical vortex model as well as with micromagnetic simulations.Comment: 9 pages, 4 figure

Universal R-C crossover in current-voltage characteristics for unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions

We report on some unusual behavior of the measured current-voltage characteristics (CVC) in artificially prepared two-dimensional unshunted array of overdamped Nb-AlO_x-Nb Josephson junctions. The obtained nonlinear CVC are found to exhibit a pronounced (and practically temperature independent) crossover at some current I_{cr}=\left(\frac{1}{2\beta_C}-1\right)I_C from a resistance R dominated state with V_R=R\sqrt{I^2-I_C^2} below I_{cr} to a capacitance C dominated state with V_C=\sqrt{\frac{\hbar}{4eC}} \sqrt{I-I_C} above I_{cr}. The origin of the observed behavior is discussed within a single-plaquette approximation assuming the conventional RSJ model with a finite capacitance and the Ambegaokar-Baratoff relation for the critical current of the single junction

Manifestation of geometric resonance in current dependence of AC susceptibility for unshunted array of Nb-AlOx-Nb Josephson junctions

A pronounced resonance-like structure has been observed in the current dependence of AC susceptibility for two-dimensional array of unshunted Nb-AlOx-Nb Josephson junctions. Using a single-plaquette approximation, we were able to successfully fit our data assuming that resonance structure is related to the geometric (inductive) properties of the array.Comment: to appear in Physica C (in press

Agroecologia e desenvolvimento sustentável.

O desenvolvimento sustentável tem suas bases conceituais assentadas na Agenda XXI de 1992, que será revisitada na Rio +20, em junho de 2012, como resultado do pacto firmado pelas Nações Unidas com o mundo, para enfrentar os desafios socioambientais e econômicos decorrentes da crise mundial iniciada na década de 1970. Assim, nos últimos 20 anos, todo o sistema econômico vem tentando se ajustar ao que é denominado desenvolvimento sustentável

Produção de mudas de algumas espécies do gênero Spondias: uma alternativa na diversificação da fruticultura de sequeiro.

Propagação por semente e formação do porta-enxerto; Propagação vegetativa: estaquia em umbuzeiro, enxertia em umbuzeiro; Considerações finais

Deciphering M-T diagram of shape memory Heusler alloys: reentrance, plateau and beyond

We present our recent results on temperature behaviour of magnetization observed in Ni_47Mn_39In_14 Heusler alloys. Three regions can be distinguished in the M-T diagram: (I) low temperature martensitic phase (with the Curie temperature T_CM = 140 K), (II) intermediate mixed phase (with the critical temperature T_MS = 230 K) exhibiting a reentrant like behavior (between T_CM and T_MS) and (III) high temperature austenitic phase (with the Curie temperature T_CA = 320 K) exhibiting a rather wide plateau region (between T_MS and T_CA). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entire M-T diagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg-Landau scenario