References of "Avila Osses, Jonathan"
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See detailInjection of spin-polarized current in a Ge-based magnetic device with coplanar contacts
Fourneau, Emile ULiege; Avila Osses, Jonathan ULiege; Silhanek, Alejandro ULiege et al

Poster (2017, November 09)

Electron spin injection and spin detection in magnetic materials are key features to the functionalization of electron spin polarization as a degree of freedom for both information processing and storage ... [more ▼]

Electron spin injection and spin detection in magnetic materials are key features to the functionalization of electron spin polarization as a degree of freedom for both information processing and storage. Currently, spin-dependent tunneling in magnetic junction devices is the most common approach to achieve efficient spin injection. However, many recent studies highlighted the interesting possibility to create spin-polarized currents in structures which combine a magnetic semiconductor, e.g. magnetic alloys based on group-IV semiconductors or diluted magnetic semiconductor compounds, forming a Schottky-like rectifying junction with a metallic ferromagnet. Although theoretical works have already addressed the performance of this structure by numerical simulations of the spin drift and spin diffusion equations, taking into account various characteristics of the ferromagnet (FM) / semiconductor (SC) interface such as barrier height and boundary roughness in 1D models, correlations with experimental results are scarce. This work aims at achieving spin injection with Ge-based magnetic structures using a rectifying junction in a coplanar architecture. We performed 2D numerical calculations of the spin drift and diffusion process in the direct neighborhood of a junction consisting of a Mn5Ge3 half-metallic ferromagnet acting as the injecting contact and an n-type Ge film, forming 3- and 4-terminal devices. Our results show that geometrical effects play a major role on the spin injection efficiency. Moreover, the simulations emphasize the asymmetry of spin accumulation at the FM/SC interface as well as a strong effect of the depletion layer caused by the Schottky contact junction. [less ▲]

Detailed reference viewed: 18 (0 ULiège)
See detailInfluence of the inhomogeneous properties of a superconducting film on the penetration of the magnetic flux
Burger, Loïc ULiege; Avila Osses, Jonathan ULiege; Nguyen, Ngoc Duy ULiege et al

Poster (2017, September 20)

We consider the penetration of magnetic flux perpendicular to a Nb superconducting film containing edge indentations and/or defects. The presence of such defects and indented edges forces the induced ... [more ▼]

We consider the penetration of magnetic flux perpendicular to a Nb superconducting film containing edge indentations and/or defects. The presence of such defects and indented edges forces the induced currents to change direction abruptly, which gives rise to discontinuity lines (d-lines). It has been recently shown, by magneto-optical means, that the shape of the d-lines contain information about the size and the shape of the indentations [1]. Moreover, in contrast with what is commonly assumed, thermomagnetic instabilities are not preferentially triggered near the manufactured indentations, but rather along smooth edges [1]. Such phenomena can lead to unexpected quenching of superconducting samples and considerably damage them, which must be avoided in applications. In this poster, we investigate whether inhomogeneous superconducting properties can be responsible for triggering magnetic flux avalanches. To this aim, we numerically model the flux penetration and determine the distribution of current lines and electric fields for a situation where the superconducting properties vary locally over a small region of the film. We consider the variation of the thickness of the film, the critical current density and the size of the discontinuity. The resulting shapes of the d-lines are deduced and compared to analytical critical state approximations. We also determine the location and the amplitude of the maximal electric field in the film and compare it to typical values which must be reached in order to trigger magnetic flux avalanches. We conclude that the investigated variations lead to levels of electric field which are of the same order of magnitude as those generated by artificial indentations. [less ▲]

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See detailModel for the penetration of magnetic flux in Nb superconducting films with lithographically defined indentations and defects due to inhomogeneities
Vanderheyden, Benoît ULiege; Avila Osses, Jonathan ULiege; Brisbois, Jérémy ULiege et al

Conference (2017, August 31)

We consider the penetration of magnetic flux perpendicularly to a Nb superconducting film containing edge indentations and/or defects. The induced currents undergo an abrupt change of direction around the ... [more ▼]

We consider the penetration of magnetic flux perpendicularly to a Nb superconducting film containing edge indentations and/or defects. The induced currents undergo an abrupt change of direction around the indentations and the defects, giving rise to discontinuity lines (d-lines). It has recently been shown, by means of magneto-optical imaging and numerical models, that the detailed structure of the d-lines generated with lithographically-defined micro-indentations carry information about their size and shape, and vary with temperature [1]. In this talk, we describe the models which can be used to describe the d-lines and discuss the effects of temperature, demagnetization, and flux creep, as well as the influence of a field-dependent critical current density on the distribution of the magnetic field. We extend the model to discontinuities produced by defects arising from inhomogeneous properties of the film and discuss the information contained in the resulting d-line structure. Last, in contrast to what has been repeatedly predicted in the literature, artificial indentations were not observed to act as preferred nucleation spots for flux avalanches [1]. To investigate this result, we estimate the levels of electric field strengthening arising near indentations and defects, and compare with the levels necessary for triggering thermomagnetic instabilities. [less ▲]

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See detailImprinting superconducting vortex footsteps in a magnetic layer
Brisbois, Jérémy ULiege; Motta, Maycon; Avila Osses, Jonathan ULiege et al

in Scientific Reports (2016), 6

Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit ... [more ▼]

Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories. [less ▲]

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See detailMagnetic flux penetration in Nb superconducting films with lithographically defined micro-indentations
Brisbois, Jérémy ULiege; Adami, Obaïd-Allah ULiege; Avila Osses, Jonathan ULiege et al

in Physical Review B (2016), 93(5), 054521

We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines ... [more ▼]

We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines (d-lines), caused by the abrupt bending of current streamlines around the indentations, depart from the expected parabolic trend close to the defect and depend on the shape and size of the indentation as well as on the temperature. These findings are backed up and compared with theoretical results obtained by numerical simulations and analytical calculations highlighting the key role played by demagnetization effects and the creep exponent n. In addition, we show that the presence of nearby indentations and submicrometer random roughness of the sample border can severely modify the flux front topology and dynamics. Strikingly, in contrast to what has been repeatedly predicted in the literature, we do not observe that indentations act as nucleation spots for flux avalanches, but they instead help to release the flux pressure and avoid thermomagnetic instabilities. [less ▲]

Detailed reference viewed: 156 (66 ULiège)