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103 results on '"Fregenal, D"'

4. Microstructural contribution to the magnetic anisotropy in Fe 1−x Ga x thin films: correlation between crystallographic texture and magnetic response.

Author

Ramírez, G A, Moya Riffo, A E, Ambrosio, L, Gómez, J E, Goijman, D, Rodríguez, L M, Fregenal, D E, Bernardi, G C, Butera, A, and Milano, J

Subjects
CRYSTAL texture, THIN films, MAGNETIC control, MAGNETIC materials, MAGNETIC anisotropy, SUBSTRATES (Materials science), MAGNETIC entropy
Abstract

In this study, we present a systematic analysis of the relation between the structural properties and magnetic anisotropies of as-grown and heat-treated polycrystalline Fe 1 − x Ga x (0.11 < x < 0.19) thin films deposited on glass and Si(100) substrates. The results show that the crystallographic texture of the films has a significant impact on the evolution of the magnetic anisotropies. The samples grown on glass do not exhibit a preferred texture while, for samples grown on Si(100), the appearance of a weak in-plane fourfold magnetic anisotropy is reported. Such anisotropy is enhanced and better defined in the heat treated samples. Via a phenomenological model we show that this anisotropy has a microstructural origin. These findings demonstrate the possibility of tuning magnetic anisotropies by growing on different substrates and/or performing thermal treatments, which in turn reinforces the possibility of developing smart magnetic switching materials for electronic applications. [ABSTRACT FROM AUTHOR]

Published
2024
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5. Experimental and theoretical results on electron emission in collisions between He targets and dressed Li$^{q+}$ (q=1,2) projectiles

Author

Fregenal, D., Monti, J. M., Fiol, J., Fainstein, P. D., Rivarola, R. D., Bernardi, G., and Suárez, S.

Subjects
Physics - Atomic Physics
Abstract

We investigate experimentally and theoretically the electron emission in collisions between He atoms and Li$^{q+}$ (q=1,2) projectiles at intermediate-high incident energies. We report on measured absolute values of double differential cross-sections, as a function of the emitted electron energy and angle, at a collision energy of 440~keV/u. The different contributions from target-ionisation, projectile-ionisation, and simultaneous target-projectile ionisation are calculated with the quantum-mechanical Continuum Distorted Wave and Continuum Distorted Wave -- Eikonal Initial State models, and with Classical Trajectory Monte Carlo simulations. There is an overall good agreement of the calculations with the experimental data for electron emission cross-sections., Comment: 19 pages, 6 figures

Published
2014
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12. Water fragmentation induced by ion impact : Fragment-ion-energy determination at different Z(P)/v regimes

Author

Cariatore, N. D., Otranto, S., Wolff, W., Luna, H., Turco, F., Fregenal, D., Bernardi, G., Suárez, S., Schuch, Reinhold, Cariatore, N. D., Otranto, S., Wolff, W., Luna, H., Turco, F., Fregenal, D., Bernardi, G., Suárez, S., and Schuch, Reinhold

Abstract

This work focuses on the energy distributions of positive water ionic fragments produced by ion impact at MeV impact energies. An improved Coulomb explosion model coupled to a classical trajectory Monte Carlo simulation is used to provide energy centroids of the fragments for the dissociation channels resulting from the removal of two to five electrons from the water molecule. This model explicitly includes the post-collisional interaction of the projectile with the resulting ionic fragments affecting their kinetic energy release spectra especially at low impact energies. Theoretical data are benchmarked against recent data collected for 220 keV Xe22+ + H2O collisions which corresponds to a large Zp/v collision parameter. To extend our tests to the low Zp/v regime, fragment species as a function of emission energy and time-of-flight were recorded in 3 MeV Li3+ collisions by using an electrostatic spectrometer and a time-of-flight mass spectrometer, respectively. Present experimental data reveals the existence of multiple-ionization processes leading to charge state up to 4+.

Published
2017
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14. Water fragmentation by bare and dressed light ions with MeV energies : Fragment-ion-energy and time-of-flight distributions

Author

Wolff, W., Luna, H., Schuch, Reinhold, Cariatore, N. D., Otranto, S., Turco, F., Fregenal, D., Bernardi, G., Suarez, S., Wolff, W., Luna, H., Schuch, Reinhold, Cariatore, N. D., Otranto, S., Turco, F., Fregenal, D., Bernardi, G., and Suarez, S.

Abstract

The energy and time-of-flight distributions of water ionic fragments produced by impact of fast atoms and bare and dressed ions; namely, H+, Li0-3+, C1+, and C2+ are reported in this work. Fragment species as a function of emission energy and time-of-flight were recorded by using an electrostatic spectrometer and a time-of-flight mass spectrometer, respectively. An improved Coulomb explosion model coupled to a classical trajectory Monte Carlo (CTMC) simulation gave the energy centroids of the fragments for the dissociation channels resulting from the removal of two to five electrons from the water molecule. For the energy distribution ranging up to 50 eV, both the experiment and model reveal an isotropic production of multiple charged oxygen ions, as well as hydrogen ions. From the ion energy distribution, relative yields of the dissociation resulting from multiple ionization were obtained as a function of the charge state, as well as for several projectile energies. Multiple-ionization yields with charge state up to 4+, were extracted from the measurements of the time-of-flight spectra, focused on the production of single and multiple charged oxygen ions. The measurements were compared to ion-water collision experiments investigated at the keV energy range available in the literature, revealing differences and similarities in the fragment-ion energy distribution.

Published
2016
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17. Colisiones ión-átomo: Una oportunidad para estudiar fenómenos dinámicos complejos

Author

González, A. D., Fregenal, D., and Suárez, S.

Subjects
colisiones, Fenómenos dinámicos complejos, lcsh:QC350-467, lcsh:Physics, lcsh:QC1-999, lcsh:Optics. Light
Abstract

La colisión de iones con átomos es un problema que data de la época de Rutherford. En las últimas décadas, la creciente sofisticación en técnicas experimentales ha permitido observar detalles que antes eran impensables, midiendo simultáneamente varias partículas y encontrando sus correlaciones. También nos encontramos con evidencias que son, en muchos casos, muy difíciles de analizar teóricamente, y a veces, difíciles de comparar con ideas previas. En este artículo se plantea el problema básico y se resumen algunos experimentos recientes. Ion-atom collisions is a subject investigated from Ruthetford's time. In the last decades, due to the accelerated advance in experimental techniques, coincidence measurements have allowed to study the problem with great detail. Lately, the experimental evidence is often very complex to be analysed theoretically, and in some cases, difficult to match with previous ideas. In the present paper the basic problema and ame recent experiments are summarised.

Published
1998

49. Atomic Pseudospin Resonance

Author

Fregenal, D., primary, Ehrenreich, T., additional, Henningsen, B., additional, Horsdal-Pedersen, E., additional, Nyvang, L., additional, and Ostrovsky, V. N., additional

Published
2001
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50. Recent experiments on the roles of projectile electrons in ion-atom collisions.

Author

Fregenal, D., Fiol, J., Sua´rez, S., Bernardi, G., Focke, P., and Gonza´lez, A. D.

Subjects
*ELECTRONS, *ION-atom collisions
Abstract

By measuring recoil-ion-electron, projectile-electron, and triple coincidences, multiple ionization differential cross sections and probabilities for impact of H, He, H[sup +], He[sup +] and He[sup ++] colliding with He, Ne, Ar and Kr have been obtained. Here we concentrate on differential measurements of multiple ionization of heavy targets produced by impact of neutral and charged H and He projectiles. In the case of H[sup +] impact, previous experiments have shown a large enhancement of electron emission associated with the ratio of Ar[sup 2+]/Ar[sup +], with a maximum at an electron velocity close to the projectile velocity for electron emission angles around 90 degrees. Both, double ionization (DI) and transfer ionization (TI) are responsible for the enhancement, which was also observed for Ne and Kr targets. New results demonstrate that, for 100 keV H[sup +]+Ar collisions, the contribution to the enhancement due to DI is larger than TI. Neutral beams produce no effect of this sort. A simultaneous projectile and target ionization contribution is discussed. [ABSTRACT FROM AUTHOR]

Published
2001

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